i2c: real DesignWare transfer chain — engine, PCI discovery, provider routing

The I2C transfer chain was stubbed end-to-end:

- i2cd's transfer path returned 'not implemented yet' for every
  transfer, and its wire format didn't match the only in-tree consumer
  (i2c-hidd sends a bare I2cTransferRequest, i2cd expected
  I2cControlRequest::Transfer).
- intel-lpss-i2cd / dw-acpi-i2cd / amd-mp2-i2cd registered an adapter
  name and parked forever without initializing the controller or
  executing a transfer.
- intel-lpss-i2cd matched only legacy ACPI HIDs, which do not exist on
  Meteor Lake / Arrow Lake platforms (LPSS I2C binds by PCI ID there,
  per Linux drivers/mfd/intel-lpss-pci.c).

Replace with real implementations:

- New shared crate drivers/i2c/designware (dw-i2c): DesignWare I2C
  master engine ported from Linux 7.1 i2c-designware-master.c and
  i2c-designware-common.c — IC_CON + SCL timing computed from ic_clk
  with Linux's exact hcnt/lcnt formulas (bxt_i2c_info 133 MHz for
  LPSS, 100 MHz for ACPI-designated blocks), SDA hold with RX-hold
  workaround, polling transfer engine with RESTART/STOP sequencing,
  TX_ABRT decode (Nack/arbitration-lost/abort/timeout), 7/10-bit
  addressing, bounded timeouts. Also provides the shared
  /scheme/<name> transfer endpoint with register-then-ready ordering.
- intel-lpss-i2cd: PCI discovery for ARL-H (0x7750/0x7751,
  0x7778-0x777b) and MTL-P (0x7e50/0x7e51, 0x7e78-0x7e7b) with 32/64-bit
  BAR0 decode, ACPI alias resolution via FixedMemory32 == BAR0 across
  /scheme/acpi/resources, legacy ACPI-HID path kept, i2cd registration
  with bounded retry, serves /scheme/i2c-lpss.
- dw-acpi-i2cd: converted from register-and-park to the shared engine,
  serves /scheme/dw-acpi-i2c.
- i2cd: real transfer routing — adapter resolution by name/alias
  (exact, normalized, last-component) and forwarding to the provider
  daemon's /scheme/<provider>/transfer endpoint.
- i2c-interface: I2cAdapterInfo gains provider_scheme + aliases
  (serde-default, wire-compatible).

Tests: dw-i2c 3, intel-lpss-i2cd 3; full workspace cargo check clean;
base cooks for x86_64-unknown-redox.

Refs: local/docs/LG-GRAM-16Z90TP-COMPATIBILITY-PLAN.md Phase 4

Cargo.lock

@@ -678,6 +678,7 @@ dependencies = [
  "anyhow",
  "common",
  "daemon",
+ "dw-i2c",
  "i2c-interface",
  "libredox",
  "log",
@@ -686,6 +687,20 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "dw-i2c"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "i2c-interface",
+ "log",
+ "redox-scheme",
+ "redox_syscall 0.9.0+rb0.3.1",
+ "ron",
+ "scheme-utils",
+ "serde",
+]
+
 [[package]]
 name = "e1000d"
 version = "0.1.0"
@@ -1250,11 +1265,14 @@ dependencies = [
  "anyhow",
  "common",
  "daemon",
+ "dw-i2c",
  "i2c-interface",
  "libredox",
  "log",
+ "redox-scheme",
  "redox_syscall 0.9.0+rb0.3.1",
  "ron",
+ "scheme-utils",
  "serde",
 ]
 

Cargo.toml

@@ -75,6 +75,7 @@ members = [
     "drivers/i2c/i2c-interface",
     "drivers/i2c/i2cd",
     "drivers/i2c/amd-mp2-i2cd",
+    "drivers/i2c/designware",
     "drivers/i2c/dw-acpi-i2cd",
     "drivers/i2c/intel-lpss-i2cd",
 

drivers/i2c/amd-mp2-i2cd/src/main.rs

@@ -57,6 +57,8 @@ fn daemon_main(daemon: daemon::Daemon, pcid_handle: &mut PciFunctionHandle) -> R
         name: format!("amd-mp2:{}", pci_config.func.name()),
         max_transaction_size: 0,
         supports_10bit_addr: false,
+        provider_scheme: String::new(),
+        aliases: Vec::new(),
     };
     let mut registration = register_adapter(&info)
         .context("failed to register AMD MP2 controller with i2cd")?;

drivers/i2c/designware/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "dw-i2c"
+description = "Synopsys DesignWare I2C master controller engine (Linux i2c-designware port)"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+log.workspace = true
+redox_syscall = { workspace = true, features = ["std"] }
+redox-scheme.workspace = true
+ron.workspace = true
+anyhow.workspace = true
+serde.workspace = true
+
+i2c-interface = { path = "../i2c-interface" }
+scheme-utils = { path = "../../../scheme-utils" }
+
+[lints]
+workspace = true

drivers/i2c/designware/src/lib.rs

@@ -0,0 +1,671 @@
+//! Synopsys DesignWare I2C master controller engine.
+//!
+//! Ported from Linux 7.1 `drivers/i2c/busses/i2c-designware-master.c` and
+//! `i2c-designware-common.c` (register model in `i2c-designware-core.h`).
+//! Polling variant: transfers complete by polling IC_STATUS with bounded
+//! timeouts instead of interrupt-driven completion, the same approach used
+//! by the U-Boot DesignWare driver. Transfer semantics (RESTART/STOP
+//! sequencing, TX_ABRT error decode, 7/10-bit addressing) follow the Linux
+//! master driver.
+
+use std::fmt;
+use std::time::{Duration, Instant};
+
+// Register offsets (i2c-designware-core.h).
+const DW_IC_CON: usize = 0x00;
+const DW_IC_TAR: usize = 0x04;
+const DW_IC_DATA_CMD: usize = 0x10;
+const DW_IC_SS_SCL_HCNT: usize = 0x14;
+const DW_IC_SS_SCL_LCNT: usize = 0x18;
+const DW_IC_FS_SCL_HCNT: usize = 0x1c;
+const DW_IC_FS_SCL_LCNT: usize = 0x20;
+const DW_IC_INTR_MASK: usize = 0x30;
+const DW_IC_RAW_INTR_STAT: usize = 0x34;
+const DW_IC_CLR_INTR: usize = 0x40;
+const DW_IC_CLR_TX_ABRT: usize = 0x54;
+const DW_IC_ENABLE: usize = 0x6c;
+const DW_IC_STATUS: usize = 0x70;
+const DW_IC_SDA_HOLD: usize = 0x7c;
+const DW_IC_TX_ABRT_SOURCE: usize = 0x80;
+const DW_IC_COMP_VERSION: usize = 0xf8;
+
+// IC_CON bits (i2c-designware-core.h).
+const IC_CON_MASTER: u32 = 1 << 0;
+const IC_CON_SPEED_FAST: u32 = 2 << 1;
+const IC_CON_10BITADDR_MASTER: u32 = 1 << 4;
+const IC_CON_RESTART_EN: u32 = 1 << 5;
+const IC_CON_SLAVE_DISABLE: u32 = 1 << 6;
+
+// IC_DATA_CMD bits: [7:0] data, [8] read, [9] stop, [10] restart.
+const IC_DATA_CMD_READ: u32 = 1 << 8;
+const IC_DATA_CMD_STOP: u32 = 1 << 9;
+const IC_DATA_CMD_RESTART: u32 = 1 << 10;
+
+// IC_STATUS bits (i2c-designware-core.h).
+const IC_STATUS_ACTIVITY: u32 = 1 << 0;
+const IC_STATUS_TFNF: u32 = 1 << 1;
+const IC_STATUS_TFE: u32 = 1 << 2;
+const IC_STATUS_RFNE: u32 = 1 << 3;
+const IC_STATUS_MASTER_ACTIVITY: u32 = 1 << 5;
+
+// IC_RAW_INTR_STAT bit for transfer abort.
+const IC_RAW_TX_ABRT: u32 = 1 << 6;
+
+// IC_TX_ABRT_SOURCE codes (i2c-designware-core.h).
+const ABRT_7B_ADDR_NOACK: u32 = 1 << 0;
+const ABRT_10ADDR1_NOACK: u32 = 1 << 1;
+const ABRT_10ADDR2_NOACK: u32 = 1 << 2;
+const ABRT_TXDATA_NOACK: u32 = 1 << 3;
+const ABRT_GCALL_NOACK: u32 = 1 << 4;
+const ABRT_MASTER_DIS: u32 = 1 << 11;
+const ABRT_ARB_LOST: u32 = 1 << 12;
+const ABRT_NOACK_MASK: u32 = ABRT_7B_ADDR_NOACK
+    | ABRT_10ADDR1_NOACK
+    | ABRT_10ADDR2_NOACK
+    | ABRT_TXDATA_NOACK
+    | ABRT_GCALL_NOACK;
+
+const IC_SDA_HOLD_MIN_VERS: u32 = 0x3131_312a; // "111*"
+const IC_SDA_HOLD_RX_SHIFT: u32 = 16;
+
+const DW_IC_TAR_10BITADDR_MASTER: u32 = 1 << 12;
+
+/// Polling budget for a single byte-level wait. HID-over-I2C workloads are
+/// small; 50 ms is generous even for a heavily loaded 100 kHz bus.
+const BYTE_WAIT_TIMEOUT: Duration = Duration::from_millis(50);
+/// Polling budget for whole-transfer completion (FIFO drain + bus idle).
+const COMPLETION_TIMEOUT: Duration = Duration::from_millis(250);
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum DwError {
+    /// Slave addressed NACKed (address or data phase).
+    Nack,
+    /// Arbitration lost (multi-master contention).
+    ArbitrationLost,
+    /// Hardware abort that is not a simple NACK.
+    Abort(u32),
+    /// Polling timeout waiting for FIFO space, data, or bus idle.
+    Timeout,
+    /// Controller reported MASTER_DIS abort (master mode disabled).
+    MasterDisabled,
+}
+
+impl fmt::Display for DwError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            DwError::Nack => write!(f, "slave NACK"),
+            DwError::ArbitrationLost => write!(f, "arbitration lost"),
+            DwError::Abort(src) => write!(f, "transfer abort (IC_TX_ABRT_SOURCE={src:#x})"),
+            DwError::Timeout => write!(f, "transfer timeout"),
+            DwError::MasterDisabled => write!(f, "master mode disabled"),
+        }
+    }
+}
+
+impl std::error::Error for DwError {}
+
+/// SCL timing parameters for one bus speed, derived from the controller
+/// clock exactly as Linux's `i2c_dw_scl_hcnt`/`i2c_dw_scl_lcnt` do.
+#[derive(Debug, Clone, Copy)]
+pub struct SclTiming {
+    pub hcnt: u32,
+    pub lcnt: u32,
+    pub sda_hold_tx: u32,
+    pub sda_fall_ns: u32,
+    pub scl_fall_ns: u32,
+}
+
+/// Bus timing inputs in the same shape Linux's intel-lpss-pci.c carries them
+/// (`bxt_i2c_info`: 133 MHz clock, sda-hold 42 ns, sda-fall 171 ns,
+/// scl-fall 208 ns).
+#[derive(Debug, Clone, Copy)]
+pub struct BusTiming {
+    pub ic_clk_hz: u32,
+    pub sda_hold_ns: u32,
+    pub sda_fall_ns: u32,
+    pub scl_fall_ns: u32,
+}
+
+/// Broxton-derived LPSS timing used by every modern Intel LPSS I2C block
+/// (ARL-H 0x7778/0x7779 and MTL-P 0x7e50/0x7e78 families per
+/// `intel-lpss-pci.c`: `.clk_rate = 133000000`, `bxt_i2c_properties`).
+pub const BXT_I2C_TIMING: BusTiming = BusTiming {
+    ic_clk_hz: 133_000_000,
+    sda_hold_ns: 42,
+    sda_fall_ns: 171,
+    scl_fall_ns: 208,
+};
+
+impl BusTiming {
+    /// Fast-mode (400 kHz) SCL counts. Formulas from
+    /// `i2c-designware-common.c:i2c_dw_scl_hcnt/lcnt`:
+    ///   hcnt = IC_CLK * (tHD;STA + tf) - 3
+    ///   lcnt = IC_CLK * (tLOW + tf) - 1
+    /// with tHD;STA = 0.6 us and tLOW = 1.3 us (I2C fast-mode spec).
+    pub fn fast_mode(&self) -> SclTiming {
+        let clk_khz = self.ic_clk_hz / 1000;
+        let hcnt = (clk_khz as u64 * (600 + self.scl_fall_ns as u64) / 1_000_000)
+            .saturating_sub(3) as u32;
+        let lcnt = (clk_khz as u64 * (1300 + self.scl_fall_ns as u64) / 1_000_000)
+            .saturating_sub(1) as u32;
+        // IC_SDA_HOLD TX value is in IC_CLK cycles (datasheet §5.11).
+        let sda_hold_tx = (clk_khz as u64 * self.sda_hold_ns as u64).div_ceil(1_000_000) as u32;
+        SclTiming {
+            hcnt,
+            lcnt,
+            sda_hold_tx,
+            sda_fall_ns: self.sda_fall_ns,
+            scl_fall_ns: self.scl_fall_ns,
+        }
+    }
+
+    /// Standard-mode (100 kHz) SCL counts: tHD;STA = 4.0 us, tLOW = 4.7 us.
+    pub fn standard_mode(&self) -> SclTiming {
+        let clk_khz = self.ic_clk_hz / 1000;
+        let hcnt = (clk_khz as u64 * (4000 + self.scl_fall_ns as u64) / 1_000_000)
+            .saturating_sub(3) as u32;
+        let lcnt = (clk_khz as u64 * (4700 + self.scl_fall_ns as u64) / 1_000_000)
+            .saturating_sub(1) as u32;
+        let sda_hold_tx = (clk_khz as u64 * self.sda_hold_ns as u64).div_ceil(1_000_000) as u32;
+        SclTiming {
+            hcnt,
+            lcnt,
+            sda_hold_tx,
+            sda_fall_ns: self.sda_fall_ns,
+            scl_fall_ns: self.scl_fall_ns,
+        }
+    }
+}
+
+/// One transfer segment: either a write of `data` or a read of `len` bytes.
+#[derive(Debug, Clone)]
+pub enum Segment {
+    Write(Vec<u8>),
+    Read(usize),
+}
+
+/// DesignWare master engine over a mapped MMIO register block.
+pub struct DwI2c {
+    base: *mut u8,
+}
+
+// The MMIO block is process-local and the driver serves transfers from a
+// single scheme handler thread.
+unsafe impl Send for DwI2c {}
+
+impl DwI2c {
+    /// # Safety
+    /// `base` must point at the start of a mapped DesignWare register block
+    /// of at least 0x100 bytes, exclusively owned by the caller.
+    pub unsafe fn new(base: *mut u8) -> Self {
+        Self { base }
+    }
+
+    fn read32(&self, reg: usize) -> u32 {
+        unsafe { (self.base.add(reg) as *const u32).read_volatile() }
+    }
+
+    fn write32(&self, reg: usize, value: u32) {
+        unsafe { (self.base.add(reg) as *mut u32).write_volatile(value) }
+    }
+
+    fn enabled(&self) -> bool {
+        self.read32(DW_IC_ENABLE) & 1 != 0
+    }
+
+    fn set_enabled(&self, enable: bool) {
+        self.write32(DW_IC_ENABLE, enable as u32);
+    }
+
+    /// Initialize the controller for master-mode operation.
+    ///
+    /// Mirrors `i2c_dw_init_master` (i2c-designware-master.c): disable,
+    /// program IC_CON and SCL counts for both speed grades, apply SDA hold
+    /// times with the RX-hold workaround, mask all interrupts (polling
+    /// driver), flush stale state, then enable.
+    pub fn init(&self, timing: &BusTiming) {
+        let fast = timing.fast_mode();
+        let standard = timing.standard_mode();
+
+        self.set_enabled(false);
+
+        let con = IC_CON_MASTER
+            | IC_CON_SPEED_FAST
+            | IC_CON_RESTART_EN
+            | IC_CON_SLAVE_DISABLE;
+        self.write32(DW_IC_CON, con);
+
+        self.write32(DW_IC_SS_SCL_HCNT, standard.hcnt);
+        self.write32(DW_IC_SS_SCL_LCNT, standard.lcnt);
+        self.write32(DW_IC_FS_SCL_HCNT, fast.hcnt);
+        self.write32(DW_IC_FS_SCL_LCNT, fast.lcnt);
+
+        // i2c_dw_set_sda_hold: only controllers at version >= 1.11 have a
+        // writable IC_SDA_HOLD; apply the TX hold and force a 1-cycle RX
+        // hold to avoid TX arbitration loss against fast slaves.
+        if self.read32(DW_IC_COMP_VERSION) >= IC_SDA_HOLD_MIN_VERS {
+            let mut hold = fast.sda_hold_tx;
+            if self.read32(DW_IC_SDA_HOLD) >> IC_SDA_HOLD_RX_SHIFT == 0 {
+                hold |= 1 << IC_SDA_HOLD_RX_SHIFT;
+            }
+            self.write32(DW_IC_SDA_HOLD, hold);
+        }
+
+        // Polling driver: no interrupt sources, clear any pending state.
+        self.write32(DW_IC_INTR_MASK, 0);
+        let _ = self.read32(DW_IC_CLR_INTR);
+        let _ = self.read32(DW_IC_CLR_TX_ABRT);
+
+        self.set_enabled(true);
+    }
+
+    fn wait_for(&self, mut condition: impl FnMut(u32) -> bool, timeout: Duration) -> Result<(), DwError> {
+        let start = Instant::now();
+        loop {
+            let status = self.read32(DW_IC_STATUS);
+            if condition(status) {
+                return Ok(());
+            }
+            if self.read32(DW_IC_RAW_INTR_STAT) & IC_RAW_TX_ABRT != 0 {
+                return Err(self.decode_abort());
+            }
+            if start.elapsed() > timeout {
+                return Err(DwError::Timeout);
+            }
+            std::thread::yield_now();
+        }
+    }
+
+    fn decode_abort(&self) -> DwError {
+        let source = self.read32(DW_IC_TX_ABRT_SOURCE);
+        let _ = self.read32(DW_IC_CLR_TX_ABRT);
+        if source & ABRT_NOACK_MASK != 0 {
+            DwError::Nack
+        } else if source & ABRT_ARB_LOST != 0 {
+            DwError::ArbitrationLost
+        } else if source & ABRT_MASTER_DIS != 0 {
+            DwError::MasterDisabled
+        } else {
+            DwError::Abort(source)
+        }
+    }
+
+    fn set_target_address(&self, address: u16, ten_bit: bool) {
+        let mut con = self.read32(DW_IC_CON);
+        if ten_bit {
+            con |= IC_CON_10BITADDR_MASTER;
+        } else {
+            con &= !IC_CON_10BITADDR_MASTER;
+        }
+        self.write32(DW_IC_CON, con);
+
+        let mut tar = u32::from(address & 0x3ff);
+        if ten_bit {
+            tar |= DW_IC_TAR_10BITADDR_MASTER;
+        }
+        self.write32(DW_IC_TAR, tar);
+    }
+
+    /// Execute a sequence of write/read segments against one slave address,
+    /// issuing a repeated START between segments and a STOP after the last
+    /// one (or leaving the bus held when `stop` is false).
+    ///
+    /// Mirrors `i2c_dw_xfer` segment handling (i2c-designware-master.c):
+    /// writes feed IC_DATA_CMD with STOP on the final byte of the final
+    /// segment, reads issue IC_DATA_CMD_READ commands (RESTART on the first
+    /// read command after a direction change) and drain RX FIFO as data
+    /// arrives.
+    pub fn xfer(
+        &self,
+        address: u16,
+        ten_bit: bool,
+        segments: &[Segment],
+        stop: bool,
+    ) -> Result<Vec<Vec<u8>>, DwError> {
+        if segments.is_empty() {
+            return Ok(Vec::new());
+        }
+        if !self.enabled() {
+            return Err(DwError::MasterDisabled);
+        }
+
+        self.set_target_address(address, ten_bit);
+        let _ = self.read32(DW_IC_CLR_TX_ABRT);
+
+        let mut reads: Vec<Vec<u8>> = Vec::new();
+        let last = segments.len() - 1;
+
+        for (index, segment) in segments.iter().enumerate() {
+            let is_last_segment = index == last;
+            match segment {
+                Segment::Write(data) => {
+                    for (byte_index, byte) in data.iter().enumerate() {
+                        let mut cmd = u32::from(*byte);
+                        if is_last_segment && byte_index == data.len() - 1 && stop {
+                            cmd |= IC_DATA_CMD_STOP;
+                        }
+                        self.wait_for(
+                            |status| status & IC_STATUS_TFNF != 0,
+                            BYTE_WAIT_TIMEOUT,
+                        )?;
+                        self.write32(DW_IC_DATA_CMD, cmd);
+                    }
+                }
+                Segment::Read(len) => {
+                    let mut buf = Vec::with_capacity(*len);
+                    for byte_index in 0..*len {
+                        let mut cmd = IC_DATA_CMD_READ;
+                        if byte_index == 0 {
+                            cmd |= IC_DATA_CMD_RESTART;
+                        }
+                        if is_last_segment && byte_index == len - 1 && stop {
+                            cmd |= IC_DATA_CMD_STOP;
+                        }
+                        self.wait_for(
+                            |status| status & IC_STATUS_TFNF != 0,
+                            BYTE_WAIT_TIMEOUT,
+                        )?;
+                        self.write32(DW_IC_DATA_CMD, cmd);
+
+                        self.wait_for(
+                            |status| status & IC_STATUS_RFNE != 0,
+                            BYTE_WAIT_TIMEOUT,
+                        )?;
+                        buf.push((self.read32(DW_IC_DATA_CMD) & 0xff) as u8);
+                    }
+                    reads.push(buf);
+                }
+            }
+        }
+
+        // Wait for the transfer to drain and the bus to go idle
+        // (i2c_dw_wait_bus_not_busy).
+        self.wait_for(
+            |status| {
+                status & IC_STATUS_TFE != 0
+                    && status & (IC_STATUS_ACTIVITY | IC_STATUS_MASTER_ACTIVITY) == 0
+            },
+            COMPLETION_TIMEOUT,
+        )?;
+
+        Ok(reads)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn bxt_fast_mode_matches_linux_formula() {
+        // 133 MHz, tHD;STA=0.6us, tLOW=1.3us, scl_fall=208ns:
+        // hcnt = 133000*808/1e6 - 3 = 104, lcnt = 133000*1508/1e6 - 1 = 199.
+        let timing = BXT_I2C_TIMING.fast_mode();
+        assert_eq!(timing.hcnt, 104);
+        assert_eq!(timing.lcnt, 199);
+        // sda_hold_tx = ceil(133000 * 42 / 1e6) = ceil(5.586) = 6.
+        assert_eq!(timing.sda_hold_tx, 6);
+    }
+
+    #[test]
+    fn bxt_standard_mode_matches_linux_formula() {
+        // hcnt = 133000*4208/1e6 - 3 = 556, lcnt = 133000*4908/1e6 - 1 = 651.
+        let timing = BXT_I2C_TIMING.standard_mode();
+        assert_eq!(timing.hcnt, 556);
+        assert_eq!(timing.lcnt, 651);
+        assert_eq!(timing.sda_hold_tx, 6);
+    }
+}
+
+pub mod endpoint {
+    //! Shared `/scheme/<name>` transfer endpoint for DesignWare-based
+    //! controller daemons. Accepts bare `I2cTransferRequest` payloads and
+    //! executes them on the matching controller's engine.
+
+    use anyhow::{Context, Result};
+    use i2c_interface::{I2cTransferRequest, I2cTransferResponse};
+    use redox_scheme::scheme::{register_sync_scheme, SchemeSync};
+    use redox_scheme::{CallerCtx, OpenResult, Socket};
+    use scheme_utils::{Blocking, HandleMap};
+    use syscall::schemev2::NewFdFlags;
+    use syscall::{Error as SysError, EBADF, EINVAL, ENOENT};
+
+    use super::{DwI2c, Segment};
+
+    /// A brought-up controller: initialized engine plus the names consumers
+    /// use to address it (driver name and ACPI aliases).
+    pub struct EndpointController {
+        pub name: String,
+        pub aliases: Vec<String>,
+        pub engine: DwI2c,
+    }
+
+    enum Handle {
+        SchemeRoot,
+        Transfer { pending: Vec<u8> },
+    }
+
+    struct Endpoint {
+        handles: HandleMap<Handle>,
+        controllers: Vec<EndpointController>,
+    }
+
+    impl Endpoint {
+        fn execute(&self, request: &I2cTransferRequest) -> I2cTransferResponse {
+            if request.segments.is_empty() {
+                return I2cTransferResponse {
+                    ok: true,
+                    read_data: Vec::new(),
+                    error: None,
+                };
+            }
+
+            let Some(controller) = self
+                .controllers
+                .iter()
+                .find(|controller| adapter_matches(&controller.name, &controller.aliases, &request.adapter))
+            else {
+                return I2cTransferResponse {
+                    ok: false,
+                    read_data: Vec::new(),
+                    error: Some(format!(
+                        "no controller matches adapter '{}'",
+                        request.adapter
+                    )),
+                };
+            };
+
+            let first = &request.segments[0];
+            let (address, ten_bit) = (first.address, first.ten_bit_address);
+            if request
+                .segments
+                .iter()
+                .any(|segment| segment.address != address || segment.ten_bit_address != ten_bit)
+            {
+                return I2cTransferResponse {
+                    ok: false,
+                    read_data: Vec::new(),
+                    error: Some("mixed-address segment sequences are not supported".to_string()),
+                };
+            }
+
+            let ops: Vec<Segment> = request
+                .segments
+                .iter()
+                .map(|segment| match &segment.op {
+                    i2c_interface::I2cTransferOp::Write(data) => Segment::Write(data.clone()),
+                    i2c_interface::I2cTransferOp::Read(len) => Segment::Read(*len),
+                })
+                .collect();
+
+            match controller.engine.xfer(address, ten_bit, &ops, request.stop) {
+                Ok(reads) => I2cTransferResponse {
+                    ok: true,
+                    read_data: reads,
+                    error: None,
+                },
+                Err(err) => I2cTransferResponse {
+                    ok: false,
+                    read_data: Vec::new(),
+                    error: Some(format!("{}: {err}", controller.name)),
+                },
+            }
+        }
+    }
+
+    /// Adapter name matching tolerant to ACPI path normalization forms:
+    /// exact match, then last-dot-component match
+    /// ("I2C0" ≡ "PC00.I2C0" ≡ "\_SB_.PC00.I2C0").
+    fn adapter_matches(name: &str, aliases: &[String], requested: &str) -> bool {
+        fn last_component(value: &str) -> &str {
+            value.rsplit('.').next().unwrap_or(value)
+        }
+
+        let normalized = requested
+            .trim_start_matches("\\_SB_.")
+            .trim_start_matches('_');
+        if name == requested || aliases.iter().any(|alias| alias == requested || alias == &normalized) {
+            return true;
+        }
+        if last_component(name) == last_component(normalized) {
+            return true;
+        }
+        aliases
+            .iter()
+            .any(|alias| last_component(alias) == last_component(normalized))
+    }
+
+    impl SchemeSync for Endpoint {
+        fn scheme_root(&mut self) -> syscall::Result<usize> {
+            Ok(self.handles.insert(Handle::SchemeRoot))
+        }
+
+        fn openat(
+            &mut self,
+            dirfd: usize,
+            path: &str,
+            _flags: usize,
+            _fcntl_flags: u32,
+            _ctx: &CallerCtx,
+        ) -> syscall::Result<OpenResult> {
+            let handle = self.handles.get(dirfd)?;
+            let segments = path.trim_matches('/');
+
+            let new_handle = match handle {
+                Handle::SchemeRoot => match segments {
+                    "transfer" => Handle::Transfer {
+                        pending: Vec::new(),
+                    },
+                    _ => return Err(SysError::new(ENOENT)),
+                },
+                _ => return Err(SysError::new(EBADF)),
+            };
+
+            let fd = self.handles.insert(new_handle);
+            Ok(OpenResult::ThisScheme {
+                number: fd,
+                flags: NewFdFlags::empty(),
+            })
+        }
+
+        fn read(
+            &mut self,
+            id: usize,
+            buf: &mut [u8],
+            offset: u64,
+            _fcntl_flags: u32,
+            _ctx: &CallerCtx,
+        ) -> syscall::Result<usize> {
+            let handle = self.handles.get_mut(id)?;
+            let pending = match handle {
+                Handle::Transfer { pending } => pending,
+                Handle::SchemeRoot => return Err(SysError::new(EBADF)),
+            };
+
+            let offset = usize::try_from(offset).map_err(|_| SysError::new(EINVAL))?;
+            if offset >= pending.len() {
+                return Ok(0);
+            }
+            let copy_len = buf.len().min(pending.len() - offset);
+            buf[..copy_len].copy_from_slice(&pending[offset..offset + copy_len]);
+            Ok(copy_len)
+        }
+
+        fn write(
+            &mut self,
+            id: usize,
+            buf: &[u8],
+            _offset: u64,
+            _fcntl_flags: u32,
+            _ctx: &CallerCtx,
+        ) -> syscall::Result<usize> {
+            if !matches!(self.handles.get(id)?, Handle::Transfer { .. }) {
+                return Err(SysError::new(EBADF));
+            }
+
+            let text = std::str::from_utf8(buf).map_err(|_| SysError::new(EINVAL))?;
+            let request: I2cTransferRequest =
+                ron::from_str(text).map_err(|_| SysError::new(EINVAL))?;
+
+            let response = self.execute(&request);
+            let pending = ron::ser::to_string(&response)
+                .map(|text| text.into_bytes())
+                .map_err(|_| SysError::new(EINVAL))?;
+
+            let handle = self.handles.get_mut(id)?;
+            let Handle::Transfer { pending: slot } = handle else {
+                return Err(SysError::new(EBADF));
+            };
+            *slot = pending;
+            Ok(buf.len())
+        }
+    }
+
+    /// Register `/scheme/<scheme_name>` and serve transfer requests forever.
+    ///
+    /// `on_ready` runs after the scheme is registered but before requests
+    /// are processed — daemons use it for their init-system readiness
+    /// notification (matching the xhcid ordering: register, then ready).
+    pub fn serve(
+        scheme_name: &str,
+        controllers: Vec<EndpointController>,
+        on_ready: impl FnOnce(),
+    ) -> Result<()> {
+        let socket = Socket::create().context("failed to create scheme socket")?;
+        let mut endpoint = Endpoint {
+            handles: HandleMap::new(),
+            controllers,
+        };
+        register_sync_scheme(&socket, scheme_name, &mut endpoint)
+            .with_context(|| format!("failed to register {scheme_name} scheme"))?;
+
+        log::info!(
+            "dw-i2c: serving /scheme/{scheme_name} with {} controller(s)",
+            endpoint.controllers.len()
+        );
+
+        on_ready();
+
+        let blocking = Blocking::new(&socket, 16);
+        blocking
+            .process_requests_blocking(endpoint)
+            .context("scheme handler exited")?;
+
+        #[allow(unreachable_code)]
+        Ok(())
+    }
+
+    #[cfg(test)]
+    mod tests {
+        use super::*;
+
+        #[test]
+        fn adapter_name_matching_forms() {
+            let aliases = vec!["PC00.I2C0".to_string()];
+            assert!(adapter_matches("intel-lpss:00--15.0", &aliases, "PC00.I2C0"));
+            assert!(adapter_matches("intel-lpss:00--15.0", &aliases, "\\_SB_.PC00.I2C0"));
+            assert!(adapter_matches("intel-lpss:00--15.0", &aliases, "I2C0"));
+            assert!(!adapter_matches("intel-lpss:00--15.0", &aliases, "I2C3"));
+        }
+    }
+}

drivers/i2c/dw-acpi-i2cd/Cargo.toml

@@ -15,6 +15,7 @@ ron.workspace = true
 acpi-resource = { path = "../../acpi-resource" }
 common = { path = "../../common" }
 daemon = { path = "../../../daemon" }
+dw-i2c = { path = "../designware" }
 i2c-interface = { path = "../i2c-interface" }
 
 [lints]

drivers/i2c/dw-acpi-i2cd/src/main.rs

@@ -13,18 +13,22 @@ use common::{MemoryType, PhysBorrowed, Prot};
 use i2c_interface::{I2cAdapterInfo, I2cControlRequest, I2cControlResponse};
 use serde::Deserialize;
 
+use dw_i2c::endpoint::EndpointController;
+use dw_i2c::{BusTiming, DwI2c};
+
 const SUPPORTED_IDS: &[&str] = &["80860F41", "808622C1", "AMDI0010", "AMDI0019", "AMDI0510"];
 
-const DW_IC_CON: usize = 0x00;
-const DW_IC_TAR: usize = 0x04;
-const DW_IC_SS_SCL_HCNT: usize = 0x14;
-const DW_IC_SS_SCL_LCNT: usize = 0x18;
-const DW_IC_DATA_CMD: usize = 0x10;
-const DW_IC_INTR_MASK: usize = 0x30;
-const DW_IC_CLR_INTR: usize = 0x40;
-const DW_IC_ENABLE: usize = 0x6C;
-const DW_IC_STATUS: usize = 0x70;
-const DW_MMIO_WINDOW: usize = DW_IC_STATUS + core::mem::size_of::<u32>();
+// Baytrail/Cherrytrail/AMD DesignWare blocks clock the controller at 100 MHz
+// (Linux i2c-designware-pcidrv.c: ehl_get_clk_rate_khz and
+// navi_amd_get_clk_rate_khz both return 100000). The fall-time constants
+// reuse the Broxton values; the formula produces slower-than-spec timings
+// on faster blocks, which is the safe direction.
+const DW_100MHZ_TIMING: BusTiming = BusTiming {
+    ic_clk_hz: 100_000_000,
+    sda_hold_ns: 42,
+    sda_fall_ns: 171,
+    scl_fall_ns: 208,
+};
 
 #[derive(Debug, Deserialize)]
 struct AmlSymbol {
@@ -53,11 +57,6 @@ struct ControllerDescriptor {
     resources: ControllerResources,
 }
 
-struct RegisteredController {
-    _mmio: Option<PhysBorrowed>,
-    _registration: File,
-}
-
 fn main() {
     common::setup_logging(
         "bus",
@@ -88,22 +87,26 @@ fn daemon_main(daemon: daemon::Daemon) -> Result<()> {
         log::info!("dw-acpi-i2cd: no supported ACPI controllers found");
     }
 
-    let mut registered = Vec::new();
+    let mut guards = Vec::new();
+    let mut endpoint_controllers = Vec::new();
     for controller in controllers {
-        match register_controller("dw-acpi", controller) {
-            Ok(controller) => registered.push(controller),
-            Err(err) => log::warn!("dw-acpi-i2cd: controller registration skipped: {err:#}"),
+        match bring_up_controller("dw-acpi", controller) {
+            Ok((endpoint, guard)) => {
+                endpoint_controllers.push(endpoint);
+                guards.push(guard);
+            }
+            Err(err) => log::warn!("dw-acpi-i2cd: controller bring-up skipped: {err:#}"),
         }
     }
 
-    daemon.ready();
-    libredox::call::setrens(0, 0).context("failed to enter null namespace")?;
-
-    log::info!("dw-acpi-i2cd: registered {} controller(s)", registered.len());
-
-    loop {
-        std::thread::park();
-    }
+    // Registrations and MMIO mappings must outlive the scheme endpoint.
+    let _guards = guards;
+    dw_i2c::endpoint::serve("dw-acpi-i2c", endpoint_controllers, || {
+        daemon.ready();
+        if let Err(err) = libredox::call::setrens(0, 0) {
+            log::error!("dw-acpi-i2cd: failed to enter null namespace: {err}");
+        }
+    })
 }
 
 fn discover_controllers(supported_ids: &[&str]) -> Result<Vec<ControllerDescriptor>> {
@@ -199,7 +202,7 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
                 address_length,
                 ..
             }) if mmio.is_none() => {
-                mmio = Some((*address as usize, (*address_length as usize).max(DW_MMIO_WINDOW)));
+                mmio = Some((*address as usize, (*address_length as usize).max(0x100)));
             }
             ResourceDescriptor::Memory32Range(Memory32RangeDescriptor {
                 minimum,
@@ -210,7 +213,7 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
                 let span = maximum.saturating_sub(*minimum).saturating_add(1) as usize;
                 mmio = Some((
                     *minimum as usize,
-                    span.max((*address_length as usize).max(DW_MMIO_WINDOW)),
+                    span.max((*address_length as usize).max(0x100)),
                 ));
             }
             ResourceDescriptor::Address32(descriptor)
@@ -219,7 +222,7 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
             {
                 mmio = Some((
                     descriptor.minimum as usize,
-                    (descriptor.address_length as usize).max(DW_MMIO_WINDOW),
+                    (descriptor.address_length as usize).max(0x100),
                 ));
             }
             ResourceDescriptor::Address64(descriptor)
@@ -230,7 +233,7 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
                     .context("64-bit MMIO base does not fit in usize")?;
                 let len = usize::try_from(descriptor.address_length)
                     .context("64-bit MMIO length does not fit in usize")?;
-                mmio = Some((base, len.max(DW_MMIO_WINDOW)));
+                mmio = Some((base, len.max(0x100)));
             }
             ResourceDescriptor::Irq(IrqDescriptor { interrupts, .. }) if irq.is_none() => {
                 irq = interrupts.first().copied().map(u32::from);
@@ -256,29 +259,31 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
     })
 }
 
-fn register_controller(prefix: &str, controller: ControllerDescriptor) -> Result<RegisteredController> {
+fn bring_up_controller(
+    prefix: &str,
+    controller: ControllerDescriptor,
+) -> Result<(EndpointController, (PhysBorrowed, File))> {
     let ControllerDescriptor {
         device,
         hid,
         resources,
     } = controller;
 
-    let mmio = match PhysBorrowed::map(
+    let mmio = PhysBorrowed::map(
         resources.mmio_base,
         resources.mmio_len,
         Prot::RW,
         MemoryType::Uncacheable,
-    ) {
-        Ok(mapping) => Some(mapping),
-        Err(err) => {
-            log::warn!(
-                "dw-acpi-i2cd: failed to map MMIO for {device} ({:#x}, len {:#x}): {err}",
-                resources.mmio_base,
-                resources.mmio_len,
-            );
-            None
-        }
-    };
+    )
+    .with_context(|| {
+        format!(
+            "failed to map MMIO for {device} ({:#x}, len {:#x})",
+            resources.mmio_base, resources.mmio_len
+        )
+    })?;
+
+    let engine = unsafe { DwI2c::new(mmio.as_ptr() as *mut u8) };
+    engine.init(&DW_100MHZ_TIMING);
 
     log::info!(
         "dw-acpi-i2cd: discovered {device} hid={hid} mmio={:#x}+{:#x} irq={:?}",
@@ -286,9 +291,6 @@ fn register_controller(prefix: &str, controller: ControllerDescriptor) -> Result
         resources.mmio_len,
         resources.irq,
     );
-    log::debug!(
-        "dw-acpi-i2cd: DesignWare regs con={DW_IC_CON:#x} tar={DW_IC_TAR:#x} data_cmd={DW_IC_DATA_CMD:#x} intr_mask={DW_IC_INTR_MASK:#x} clr_intr={DW_IC_CLR_INTR:#x} enable={DW_IC_ENABLE:#x} ss_hcnt={DW_IC_SS_SCL_HCNT:#x} ss_lcnt={DW_IC_SS_SCL_LCNT:#x}",
-    );
 
     let info = I2cAdapterInfo {
         id: 0,
@@ -299,6 +301,8 @@ fn register_controller(prefix: &str, controller: ControllerDescriptor) -> Result
             .as_ref()
             .map(|bus| bus.access_mode_10bit)
             .unwrap_or(false),
+        provider_scheme: "dw-acpi-i2c".to_string(),
+        aliases: vec![device.clone()],
     };
     let mut registration = register_adapter(&info)
         .with_context(|| format!("failed to register {device} with i2cd"))?;
@@ -314,18 +318,36 @@ fn register_controller(prefix: &str, controller: ControllerDescriptor) -> Result
         }
     }
 
-    Ok(RegisteredController {
-        _mmio: mmio,
-        _registration: registration,
-    })
+    let endpoint = EndpointController {
+        name: format!("{prefix}:{device}"),
+        aliases: vec![device],
+        engine,
+    };
+    Ok((endpoint, (mmio, registration)))
 }
 
 fn register_adapter(info: &I2cAdapterInfo) -> Result<File> {
-    let mut file = OpenOptions::new()
-        .read(true)
-        .write(true)
-        .open("/scheme/i2c/register")
-        .context("failed to open /scheme/i2c/register")?;
+    // i2cd is ordered before us via init requires_weak, but scheme
+    // registration is asynchronous — tolerate a short startup skew instead
+    // of permanently losing the controller.
+    let mut file = None;
+    for attempt in 0..100 {
+        match OpenOptions::new()
+            .read(true)
+            .write(true)
+            .open("/scheme/i2c/register")
+        {
+            Ok(opened) => {
+                file = Some(opened);
+                break;
+            }
+            Err(err) if attempt == 99 => {
+                return Err(err).context("failed to open /scheme/i2c/register");
+            }
+            Err(_) => std::thread::sleep(std::time::Duration::from_millis(50)),
+        }
+    }
+    let mut file = file.context("failed to open /scheme/i2c/register")?;
     let payload = ron::ser::to_string(&I2cControlRequest::RegisterAdapter { info: info.clone() })
         .context("failed to encode I2C adapter registration")?;
     file.write_all(payload.as_bytes())

drivers/i2c/i2c-interface/src/lib.rs

@@ -61,6 +61,17 @@ pub struct I2cAdapterInfo {
     pub name: String,
     pub max_transaction_size: usize,
     pub supports_10bit_addr: bool,
+    /// Scheme name of the provider daemon that executes transfers for this
+    /// adapter (e.g. "i2c-lpss" → `/scheme/i2c-lpss/transfer`). Empty when the
+    /// adapter is registered by a daemon that cannot execute transfers.
+    #[serde(default)]
+    pub provider_scheme: String,
+    /// Alternative names that identify this adapter in transfer requests —
+    /// typically the ACPI path of the controller (e.g. "PC00.I2C0"), which is
+    /// what HID-over-I2C consumers obtain from the device's `_CRS`
+    /// `I2cSerialBus` resource source.
+    #[serde(default)]
+    pub aliases: Vec<String>,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]

drivers/i2c/i2cd/src/main.rs

@@ -23,7 +23,6 @@ enum Handle {
 
 struct AdapterEntry {
     info: I2cAdapterInfo,
-    provider_handle: usize,
 }
 
 struct I2cDaemon {
@@ -85,44 +84,77 @@ impl I2cDaemon {
         Self::set_pending_response(handle, I2cControlResponse::AdapterList(adapters))
     }
 
-    fn queue_transfer_stub(
-        handle: &mut Handle,
-        adapter: &I2cAdapterInfo,
-        request: &I2cTransferRequest,
-    ) -> syscall::Result<()> {
-        let write_bytes = request
-            .segments
-            .iter()
-            .filter_map(|segment| match &segment.op {
-                i2c_interface::I2cTransferOp::Write(bytes) => Some(bytes.len()),
-                i2c_interface::I2cTransferOp::Read(_) => None,
+    /// Resolve an adapter by request name. Consumers identify adapters by the
+    /// ACPI resource-source string from the device's `_CRS` (e.g.
+    /// "\_SB_.PC00.I2C0"), so matching is tolerant to normalization forms:
+    /// exact name/alias match first, then last-dot-component match.
+    fn resolve_adapter(&self, requested: &str) -> Option<&I2cAdapterInfo> {
+        fn last_component(value: &str) -> &str {
+            value.rsplit('.').next().unwrap_or(value)
+        }
+
+        let normalized = requested
+            .trim_start_matches("\\_SB_.")
+            .trim_start_matches('_');
+
+        self.adapters
+            .values()
+            .map(|entry| &entry.info)
+            .find(|info| {
+                info.name == requested
+                    || info
+                        .aliases
+                        .iter()
+                        .any(|alias| alias == requested || alias == &normalized)
+                    || last_component(&info.name) == last_component(normalized)
+                    || info
+                        .aliases
+                        .iter()
+                        .any(|alias| last_component(alias) == last_component(normalized))
             })
-            .sum::<usize>();
-        let read_segments = request
-            .segments
-            .iter()
-            .filter(|segment| matches!(segment.op, i2c_interface::I2cTransferOp::Read(_)))
-            .count();
+    }
 
-        log::info!(
-            "i2cd: routing transfer to adapter {} ({}) name={} segments={} write_bytes={} read_segments={} stop={} (stubbed)",
-            adapter.id,
-            adapter.name,
-            request.adapter,
-            request.segments.len(),
-            write_bytes,
-            read_segments,
-            request.stop,
-        );
+    /// Forward a transfer to the provider daemon that owns the adapter's
+    /// hardware: write the request to `/scheme/<provider>/transfer` and read
+    /// back the response. The wire format is the bare `I2cTransferRequest` /
+    /// `I2cTransferResponse` pair that in-tree consumers (i2c-hidd) speak.
+    fn forward_transfer(request: &I2cTransferRequest, info: &I2cAdapterInfo) -> I2cTransferResponse {
+        let fail = |message: String| I2cTransferResponse {
+            ok: false,
+            read_data: Vec::new(),
+            error: Some(message),
+        };
 
-        Self::set_pending_response(
-            handle,
-            I2cControlResponse::TransferResult(I2cTransferResponse {
-                ok: false,
-                read_data: Vec::new(),
-                error: Some(String::from("I2C controller transfer path is not implemented yet")),
-            }),
-        )
+        if info.provider_scheme.is_empty() {
+            return fail(format!(
+                "adapter '{}' has no transfer provider",
+                info.name
+            ));
+        }
+
+        let path = format!("/scheme/{}/transfer", info.provider_scheme);
+        let mut file = match std::fs::OpenOptions::new().read(true).write(true).open(&path) {
+            Ok(file) => file,
+            Err(err) => return fail(format!("cannot open {path}: {err}")),
+        };
+
+        let payload = match ron::ser::to_string(request) {
+            Ok(payload) => payload,
+            Err(err) => return fail(format!("cannot encode transfer request: {err}")),
+        };
+        if let Err(err) = std::io::Write::write_all(&mut file, payload.as_bytes()) {
+            return fail(format!("cannot write transfer to {path}: {err}"));
+        }
+
+        let mut text = String::new();
+        if let Err(err) = std::io::Read::read_to_string(&mut file, &mut text) {
+            return fail(format!("cannot read transfer response from {path}: {err}"));
+        }
+
+        match ron::from_str::<I2cTransferResponse>(&text) {
+            Ok(response) => response,
+            Err(err) => fail(format!("invalid transfer response from {path}: {err}")),
+        }
     }
 
     fn copy_pending(handle: &mut Handle, buf: &mut [u8], offset: u64) -> syscall::Result<usize> {
@@ -250,6 +282,46 @@ impl SchemeSync for I2cDaemon {
         _fcntl_flags: u32,
         _ctx: &CallerCtx,
     ) -> syscall::Result<usize> {
+        // The transfer endpoint speaks the bare I2cTransferRequest /
+        // I2cTransferResponse wire format (what i2c-hidd and other in-tree
+        // consumers use); every other endpoint speaks I2cControlRequest.
+        if matches!(self.handles.get(id)?, Handle::Transfer { .. }) {
+            let text = std::str::from_utf8(buf).map_err(|_| SysError::new(EINVAL))?;
+            let transfer: I2cTransferRequest =
+                ron::from_str(text).map_err(|_| SysError::new(EINVAL))?;
+
+            let response = match self.resolve_adapter(&transfer.adapter) {
+                Some(info) => {
+                    let info = info.clone();
+                    log::debug!(
+                        "i2cd: routing transfer for '{}' to provider '{}' ({})",
+                        transfer.adapter,
+                        info.provider_scheme,
+                        info.name,
+                    );
+                    Self::forward_transfer(&transfer, &info)
+                }
+                None => I2cTransferResponse {
+                    ok: false,
+                    read_data: Vec::new(),
+                    error: Some(format!(
+                        "no registered adapter matches '{}'",
+                        transfer.adapter
+                    )),
+                },
+            };
+
+            let pending = ron::ser::to_string(&response)
+                .map(|text| text.into_bytes())
+                .map_err(|_| SysError::new(EINVAL))?;
+            let handle = self.handles.get_mut(id)?;
+            let Handle::Transfer { pending: slot } = handle else {
+                return Err(SysError::new(EBADF));
+            };
+            *slot = pending;
+            return Ok(buf.len());
+        }
+
         let request = Self::deserialize_request(buf)?;
 
         match request {
@@ -262,7 +334,6 @@ impl SchemeSync for I2cDaemon {
                     adapter_id,
                     AdapterEntry {
                         info: info.clone(),
-                        provider_handle: id,
                     },
                 );
 
@@ -308,21 +379,12 @@ impl SchemeSync for I2cDaemon {
                 request,
             } => {
                 let entry = self.adapters.get(&adapter_id).ok_or(SysError::new(ENOENT))?;
-                log::debug!(
-                    "i2cd: transfer requested for adapter {} via provider fd {}",
-                    adapter_id,
-                    entry.provider_handle,
-                );
+                let info = entry.info.clone();
+                let response = Self::forward_transfer(&request, &info);
 
-                let adapter_info = entry.info.clone();
                 let handle = self.handles.get_mut(id)?;
-                match handle {
-                    Handle::Transfer { .. } => {
-                        Self::queue_transfer_stub(handle, &adapter_info, &request)?;
-                        Ok(buf.len())
-                    }
-                    _ => Err(SysError::new(EINVAL)),
-                }
+                Self::set_pending_response(handle, I2cControlResponse::TransferResult(response))?;
+                Ok(buf.len())
             }
         }
     }

drivers/i2c/intel-lpss-i2cd/Cargo.toml

@@ -8,6 +8,7 @@ edition = "2021"
 anyhow.workspace = true
 log.workspace = true
 redox_syscall = { workspace = true, features = ["std"] }
+redox-scheme.workspace = true
 libredox.workspace = true
 serde.workspace = true
 ron.workspace = true
@@ -15,7 +16,9 @@ ron.workspace = true
 acpi-resource = { path = "../../acpi-resource" }
 common = { path = "../../common" }
 daemon = { path = "../../../daemon" }
+dw-i2c = { path = "../designware" }
 i2c-interface = { path = "../i2c-interface" }
+scheme-utils = { path = "../../../scheme-utils" }
 
 [lints]
 workspace = true

drivers/i2c/intel-lpss-i2cd/src/main.rs

@@ -1,3 +1,14 @@
+//! Intel LPSS I2C controller daemon.
+//!
+//! Discovery follows Linux 7.1 `drivers/mfd/intel-lpss-pci.c`: modern
+//! platforms (Meteor Lake, Arrow Lake) bind the LPSS I2C blocks by PCI ID,
+//! while older platforms (Haswell through some CNL boards) expose them as
+//! ACPI devices with LPSS HIDs. Both paths converge on the same DesignWare
+//! engine (`dw.rs`, ported from Linux's i2c-designware master driver).
+//!
+//! The daemon registers each controller with i2cd and serves
+//! `/scheme/i2c-lpss/transfer`, executing real I2C transactions on hardware.
+
 use std::collections::BTreeMap;
 use std::fs::{self, File, OpenOptions};
 use std::io::{Read, Write};
@@ -13,18 +24,32 @@ use common::{MemoryType, PhysBorrowed, Prot};
 use i2c_interface::{I2cAdapterInfo, I2cControlRequest, I2cControlResponse};
 use serde::Deserialize;
 
-const SUPPORTED_IDS: &[&str] = &["INT33C2", "INT33C3", "INT3432", "INT3433", "INTC10EF"];
+use dw_i2c::endpoint::EndpointController;
+use dw_i2c::{DwI2c, BXT_I2C_TIMING};
 
-const DW_IC_CON: usize = 0x00;
-const DW_IC_TAR: usize = 0x04;
-const DW_IC_SS_SCL_HCNT: usize = 0x14;
-const DW_IC_SS_SCL_LCNT: usize = 0x18;
-const DW_IC_DATA_CMD: usize = 0x10;
-const DW_IC_INTR_MASK: usize = 0x30;
-const DW_IC_CLR_INTR: usize = 0x40;
-const DW_IC_ENABLE: usize = 0x6C;
-const DW_IC_STATUS: usize = 0x70;
-const DW_MMIO_WINDOW: usize = DW_IC_STATUS + core::mem::size_of::<u32>();
+const SUPPORTED_ACPI_IDS: &[&str] = &["INT33C2", "INT33C3", "INT3432", "INT3433", "INTC10EF"];
+
+/// Intel LPSS I2C PCI IDs, ported from Linux 7.1
+/// `drivers/mfd/intel-lpss-pci.c` (entries carrying `*_i2c_info`).
+/// All of these use the Broxton-derived timing (`bxt_i2c_info`, 133 MHz).
+const LPSS_I2C_PCI_IDS: &[u16] = &[
+    // ARL-H (0x7750/0x7751, 0x7778-0x777b)
+    0x7750, 0x7751, 0x7778, 0x7779, 0x777a, 0x777b,
+    // MTL-P (0x7e50/0x7e51, 0x7e78-0x7e7b)
+    0x7e50, 0x7e51, 0x7e78, 0x7e79, 0x7e7a, 0x7e7b,
+];
+
+const PCI_VENDOR_INTEL: u16 = 0x8086;
+const PCI_CLASS_SERIAL_BUS: u8 = 0x0c;
+const PCI_SUBCLASS_I2C: u8 = 0x80;
+
+struct Controller {
+    name: String,
+    aliases: Vec<String>,
+    engine: DwI2c,
+    registration: File,
+    mmio: PhysBorrowed,
+}
 
 #[derive(Debug, Deserialize)]
 struct AmlSymbol {
@@ -47,17 +72,12 @@ struct ControllerResources {
 }
 
 #[derive(Debug)]
-struct ControllerDescriptor {
+struct DiscoveredController {
     device: String,
     hid: String,
     resources: ControllerResources,
 }
 
-struct RegisteredController {
-    _mmio: Option<PhysBorrowed>,
-    _registration: File,
-}
-
 fn main() {
     common::setup_logging(
         "bus",
@@ -82,31 +102,256 @@ fn daemon_runner(daemon: daemon::Daemon) -> ! {
 fn daemon_main(daemon: daemon::Daemon) -> Result<()> {
     common::init();
 
-    let controllers = discover_controllers(SUPPORTED_IDS)
-        .context("failed to discover Intel LPSS ACPI I2C controllers")?;
-    if controllers.is_empty() {
-        log::info!("intel-lpss-i2cd: no supported ACPI controllers found");
-    }
+    let mut controllers = Vec::new();
 
-    let mut registered = Vec::new();
-    for controller in controllers {
-        match register_controller("intel-lpss", controller) {
-            Ok(controller) => registered.push(controller),
-            Err(err) => log::warn!("intel-lpss-i2cd: controller registration skipped: {err:#}"),
+    for discovered in discover_pci_controllers() {
+        match bring_up_controller(discovered) {
+            Ok(controller) => controllers.push(controller),
+            Err(err) => log::warn!("intel-lpss-i2cd: PCI controller bring-up skipped: {err:#}"),
         }
     }
 
-    daemon.ready();
-    libredox::call::setrens(0, 0).context("failed to enter null namespace")?;
-
-    log::info!("intel-lpss-i2cd: registered {} controller(s)", registered.len());
-
-    loop {
-        std::thread::park();
+    for discovered in discover_acpi_controllers(SUPPORTED_ACPI_IDS)
+        .context("failed to discover Intel LPSS ACPI I2C controllers")?
+    {
+        match bring_up_controller(discovered) {
+            Ok(controller) => controllers.push(controller),
+            Err(err) => log::warn!("intel-lpss-i2cd: ACPI controller bring-up skipped: {err:#}"),
+        }
     }
+
+    if controllers.is_empty() {
+        log::info!("intel-lpss-i2cd: no supported controllers found (PCI or ACPI)");
+    }
+
+    // i2cd registrations and MMIO mappings must outlive the scheme endpoint.
+    let mut guards = Vec::new();
+    let endpoint_controllers: Vec<EndpointController> = controllers
+        .into_iter()
+        .map(|controller| {
+            let Controller {
+                name,
+                aliases,
+                engine,
+                registration,
+                mmio,
+            } = controller;
+            guards.push((registration, mmio));
+            EndpointController {
+                name,
+                aliases,
+                engine,
+            }
+        })
+        .collect();
+
+    // Register the scheme first, then notify init (xhcid ordering) so a
+    // `type = { scheme = "i2c-lpss" }` service only reports ready once the
+    // scheme path actually exists.
+    dw_i2c::endpoint::serve("i2c-lpss", endpoint_controllers, || {
+        daemon.ready();
+        if let Err(err) = libredox::call::setrens(0, 0) {
+            log::error!("intel-lpss-i2cd: failed to enter null namespace: {err}");
+        }
+    })
 }
 
-fn discover_controllers(supported_ids: &[&str]) -> Result<Vec<ControllerDescriptor>> {
+// ---------------------------------------------------------------------------
+// Controller bring-up: MMIO map, engine init, i2cd registration
+// ---------------------------------------------------------------------------
+
+fn bring_up_controller(discovered: DiscoveredController) -> Result<Controller> {
+    let mmio = PhysBorrowed::map(
+        discovered.resources.mmio_base,
+        discovered.resources.mmio_len,
+        Prot::RW,
+        MemoryType::Uncacheable,
+    )
+    .with_context(|| {
+        format!(
+            "failed to map MMIO for {} ({:#x}, len {:#x})",
+            discovered.device, discovered.resources.mmio_base, discovered.resources.mmio_len
+        )
+    })?;
+
+    let engine = unsafe { DwI2c::new(mmio.as_ptr() as *mut u8) };
+    engine.init(&BXT_I2C_TIMING);
+
+    let name = format!("intel-lpss:{}", discovered.device);
+    let aliases = discover_acpi_aliases(discovered.resources.mmio_base);
+
+    log::info!(
+        "intel-lpss-i2cd: controller {} hid={} mmio={:#x}+{:#x} irq={:?} aliases={:?}",
+        name,
+        discovered.hid,
+        discovered.resources.mmio_base,
+        discovered.resources.mmio_len,
+        discovered.resources.irq,
+        aliases,
+    );
+
+    let info = I2cAdapterInfo {
+        id: 0,
+        name: name.clone(),
+        max_transaction_size: 0,
+        supports_10bit_addr: discovered
+            .resources
+            .serial_bus
+            .as_ref()
+            .map(|bus| bus.access_mode_10bit)
+            .unwrap_or(true),
+        provider_scheme: "i2c-lpss".to_string(),
+        aliases: aliases.clone(),
+    };
+    let mut registration = register_adapter(&info)
+        .with_context(|| format!("failed to register {name} with i2cd"))?;
+    let response = read_registration_response(&mut registration)
+        .with_context(|| format!("failed to read i2cd registration response for {name}"))?;
+
+    match response {
+        I2cControlResponse::AdapterRegistered { id } => {
+            log::info!("intel-lpss-i2cd: adapter {name} registered with i2cd as {id}");
+        }
+        other => {
+            log::warn!("intel-lpss-i2cd: unexpected i2cd registration response for {name}: {other:?}");
+        }
+    }
+
+    Ok(Controller {
+        name,
+        aliases,
+        engine,
+        registration,
+        mmio,
+    })
+}
+
+fn register_adapter(info: &I2cAdapterInfo) -> Result<File> {
+    // i2cd is ordered before us via init requires_weak, but scheme
+    // registration is asynchronous — tolerate a short startup skew instead
+    // of permanently losing the controller.
+    let mut file = None;
+    for attempt in 0..100 {
+        match OpenOptions::new()
+            .read(true)
+            .write(true)
+            .open("/scheme/i2c/register")
+        {
+            Ok(opened) => {
+                file = Some(opened);
+                break;
+            }
+            Err(err) if attempt == 99 => {
+                return Err(err).context("failed to open /scheme/i2c/register");
+            }
+            Err(_) => std::thread::sleep(std::time::Duration::from_millis(50)),
+        }
+    }
+    let mut file = file.context("failed to open /scheme/i2c/register")?;
+
+    let payload = ron::ser::to_string(&I2cControlRequest::RegisterAdapter { info: info.clone() })
+        .context("failed to encode I2C adapter registration")?;
+    file.write_all(payload.as_bytes())
+        .context("failed to send I2C adapter registration")?;
+    Ok(file)
+}
+
+fn read_registration_response(file: &mut File) -> Result<I2cControlResponse> {
+    let mut buffer = vec![0_u8; 4096];
+    let count = file
+        .read(&mut buffer)
+        .context("failed to read I2C registration response")?;
+    buffer.truncate(count);
+    let text = std::str::from_utf8(&buffer).context("I2C registration response was not UTF-8")?;
+    ron::from_str(text).context("failed to decode I2C registration response")
+}
+
+// ---------------------------------------------------------------------------
+// PCI discovery (Linux intel-lpss-pci.c model)
+// ---------------------------------------------------------------------------
+
+fn discover_pci_controllers() -> Vec<DiscoveredController> {
+    let entries = match fs::read_dir("/scheme/pci") {
+        Ok(entries) => entries,
+        Err(err) => {
+            log::warn!("intel-lpss-i2cd: cannot read /scheme/pci: {err}");
+            return Vec::new();
+        }
+    };
+
+    let mut out = Vec::new();
+    for entry in entries.flatten() {
+        let config_path = entry.path().join("config");
+        let Ok(config) = fs::read(&config_path) else {
+            continue;
+        };
+        if config.len() < 0x40 {
+            continue;
+        }
+        let vendor = u16::from_le_bytes([config[0x00], config[0x01]]);
+        let device = u16::from_le_bytes([config[0x02], config[0x03]]);
+        let class_code = config[0x0b];
+        let subclass = config[0x0a];
+        if vendor != PCI_VENDOR_INTEL
+            || class_code != PCI_CLASS_SERIAL_BUS
+            || subclass != PCI_SUBCLASS_I2C
+            || !LPSS_I2C_PCI_IDS.contains(&device)
+        {
+            continue;
+        }
+
+        let Some(mmio_base) = pci_bar0_address(&config) else {
+            log::warn!("intel-lpss-i2cd: {device:04x} has no usable BAR0, skipped");
+            continue;
+        };
+
+        let location = entry
+            .file_name()
+            .to_str()
+            .map(str::to_owned)
+            .unwrap_or_else(|| format!("pci-{device:04x}"));
+        let irq = config[0x3c];
+        let irq = (irq != 0 && irq != 0xff).then_some(u32::from(irq));
+
+        out.push(DiscoveredController {
+            device: location,
+            hid: format!("pci:8086:{device:04x}"),
+            resources: ControllerResources {
+                mmio_base,
+                mmio_len: 0x1000,
+                irq,
+                serial_bus: None,
+            },
+        });
+    }
+
+    out
+}
+
+/// Extract a usable memory BAR0 from raw PCI config space. Handles both
+/// 32-bit and 64-bit memory BARs; returns the CPU-physical base address.
+fn pci_bar0_address(config: &[u8]) -> Option<usize> {
+    let bar_lo = u32::from_le_bytes([config[0x10], config[0x11], config[0x12], config[0x13]]);
+    if bar_lo == 0 || bar_lo & 1 != 0 {
+        // Not present or an I/O-space BAR; LPSS I2C is always memory-mapped.
+        return None;
+    }
+    let is_64bit = (bar_lo >> 1) & 0x3 == 0x2;
+    let base_lo = u64::from(bar_lo & !0xf);
+    let base = if is_64bit {
+        let bar_hi = u32::from_le_bytes([config[0x14], config[0x15], config[0x16], config[0x17]]);
+        base_lo | (u64::from(bar_hi) << 32)
+    } else {
+        base_lo
+    };
+    (base != 0).then_some(base as usize)
+}
+
+// ---------------------------------------------------------------------------
+// ACPI discovery (legacy LPSS HID model)
+// ---------------------------------------------------------------------------
+
+fn discover_acpi_controllers(supported_ids: &[&str]) -> Result<Vec<DiscoveredController>> {
     let mut matched = BTreeMap::new();
 
     let entries = match fs::read_dir("/scheme/acpi/symbols") {
@@ -149,7 +394,7 @@ fn discover_controllers(supported_ids: &[&str]) -> Result<Vec<ControllerDescript
     for (device, hid) in matched {
         let resources = read_controller_resources(&device)
             .with_context(|| format!("failed to read resources for {device}"))?;
-        controllers.push(ControllerDescriptor {
+        controllers.push(DiscoveredController {
             device,
             hid,
             resources,
@@ -199,7 +444,7 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
                 address_length,
                 ..
             }) if mmio.is_none() => {
-                mmio = Some((*address as usize, (*address_length as usize).max(DW_MMIO_WINDOW)));
+                mmio = Some((*address as usize, (*address_length as usize).max(0x100)));
             }
             ResourceDescriptor::Memory32Range(Memory32RangeDescriptor {
                 minimum,
@@ -208,10 +453,7 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
                 ..
             }) if mmio.is_none() && maximum >= minimum => {
                 let span = maximum.saturating_sub(*minimum).saturating_add(1) as usize;
-                mmio = Some((
-                    *minimum as usize,
-                    span.max((*address_length as usize).max(DW_MMIO_WINDOW)),
-                ));
+                mmio = Some((*minimum as usize, span.max((*address_length as usize).max(0x100))));
             }
             ResourceDescriptor::Address32(descriptor)
                 if mmio.is_none()
@@ -219,7 +461,7 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
             {
                 mmio = Some((
                     descriptor.minimum as usize,
-                    (descriptor.address_length as usize).max(DW_MMIO_WINDOW),
+                    (descriptor.address_length as usize).max(0x100),
                 ));
             }
             ResourceDescriptor::Address64(descriptor)
@@ -230,7 +472,7 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
                     .context("64-bit MMIO base does not fit in usize")?;
                 let len = usize::try_from(descriptor.address_length)
                     .context("64-bit MMIO length does not fit in usize")?;
-                mmio = Some((base, len.max(DW_MMIO_WINDOW)));
+                mmio = Some((base, len.max(0x100)));
             }
             ResourceDescriptor::Irq(IrqDescriptor { interrupts, .. }) if irq.is_none() => {
                 irq = interrupts.first().copied().map(u32::from);
@@ -256,91 +498,34 @@ fn read_controller_resources(device: &str) -> Result<ControllerResources> {
     })
 }
 
-fn register_controller(prefix: &str, controller: ControllerDescriptor) -> Result<RegisteredController> {
-    let ControllerDescriptor {
-        device,
-        hid,
-        resources,
-    } = controller;
-
-    let mmio = match PhysBorrowed::map(
-        resources.mmio_base,
-        resources.mmio_len,
-        Prot::RW,
-        MemoryType::Uncacheable,
-    ) {
-        Ok(mapping) => Some(mapping),
-        Err(err) => {
-            log::warn!(
-                "intel-lpss-i2cd: failed to map MMIO for {device} ({:#x}, len {:#x}): {err}",
-                resources.mmio_base,
-                resources.mmio_len,
-            );
-            None
-        }
+/// Find the ACPI device path whose `_CRS` FixedMemory32 window matches this
+/// controller's MMIO base. That path ("PC00.I2C0") is what HID-over-I2C
+/// devices name in their `I2cSerialBus` resource source, so it is the alias
+/// consumers will use to address this adapter.
+fn discover_acpi_aliases(mmio_base: usize) -> Vec<String> {
+    let Ok(entries) = fs::read_dir("/scheme/acpi/resources") else {
+        return Vec::new();
     };
 
-    log::info!(
-        "intel-lpss-i2cd: discovered {device} hid={hid} mmio={:#x}+{:#x} irq={:?}",
-        resources.mmio_base,
-        resources.mmio_len,
-        resources.irq,
-    );
-    log::debug!(
-        "intel-lpss-i2cd: DesignWare regs con={DW_IC_CON:#x} tar={DW_IC_TAR:#x} data_cmd={DW_IC_DATA_CMD:#x} intr_mask={DW_IC_INTR_MASK:#x} clr_intr={DW_IC_CLR_INTR:#x} enable={DW_IC_ENABLE:#x} ss_hcnt={DW_IC_SS_SCL_HCNT:#x} ss_lcnt={DW_IC_SS_SCL_LCNT:#x}",
-    );
-
-    let info = I2cAdapterInfo {
-        id: 0,
-        name: format!("{prefix}:{device}"),
-        max_transaction_size: 0,
-        supports_10bit_addr: resources
-            .serial_bus
-            .as_ref()
-            .map(|bus| bus.access_mode_10bit)
-            .unwrap_or(false),
-    };
-    let mut registration = register_adapter(&info)
-        .with_context(|| format!("failed to register {device} with i2cd"))?;
-    let response = read_registration_response(&mut registration)
-        .with_context(|| format!("failed to read i2cd registration response for {device}"))?;
-
-    match response {
-        I2cControlResponse::AdapterRegistered { id } => {
-            log::info!("intel-lpss-i2cd: adapter {device} registered with i2cd as {id}");
-        }
-        other => {
-            anyhow::bail!("unexpected i2cd registration response for {device}: {other:?}");
+    let mut aliases = Vec::new();
+    for entry in entries.flatten() {
+        let Ok(contents) = fs::read_to_string(entry.path()) else {
+            continue;
+        };
+        let Ok(resources) = ron::from_str::<Vec<ResourceDescriptor>>(&contents) else {
+            continue;
+        };
+        let matches_base = resources.iter().any(|resource| match resource {
+            ResourceDescriptor::FixedMemory32(descriptor) => descriptor.address as usize == mmio_base,
+            _ => false,
+        });
+        if matches_base {
+            if let Some(name) = entry.file_name().to_str() {
+                aliases.push(name.to_owned());
+            }
         }
     }
-
-    Ok(RegisteredController {
-        _mmio: mmio,
-        _registration: registration,
-    })
-}
-
-fn register_adapter(info: &I2cAdapterInfo) -> Result<File> {
-    let mut file = OpenOptions::new()
-        .read(true)
-        .write(true)
-        .open("/scheme/i2c/register")
-        .context("failed to open /scheme/i2c/register")?;
-    let payload = ron::ser::to_string(&I2cControlRequest::RegisterAdapter { info: info.clone() })
-        .context("failed to encode I2C adapter registration")?;
-    file.write_all(payload.as_bytes())
-        .context("failed to send I2C adapter registration")?;
-    Ok(file)
-}
-
-fn read_registration_response(file: &mut File) -> Result<I2cControlResponse> {
-    let mut buffer = vec![0_u8; 4096];
-    let count = file
-        .read(&mut buffer)
-        .context("failed to read I2C registration response")?;
-    buffer.truncate(count);
-    let text = std::str::from_utf8(&buffer).context("I2C registration response was not UTF-8")?;
-    ron::from_str(text).context("failed to decode I2C registration response")
+    aliases
 }
 
 fn eisa_id_from_integer(integer: u64) -> String {
@@ -359,3 +544,32 @@ fn eisa_id_from_integer(integer: u64) -> String {
         "{vendor_1}{vendor_2}{vendor_3}{device_1:01X}{device_2:01X}{device_3:01X}{device_4:01X}"
     )
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn bar0_32bit_memory() {
+        let mut config = [0u8; 0x40];
+        config[0x10..0x14].copy_from_slice(&0x5019_2de0u32.to_le_bytes());
+        assert_eq!(pci_bar0_address(&config), Some(0x5019_2de0));
+    }
+
+    #[test]
+    fn bar0_64bit_memory() {
+        let mut config = [0u8; 0x40];
+        // 64-bit BAR: flags bits [2:1] == 0b10, base 0x5019_92de_0000.
+        config[0x10..0x14].copy_from_slice(&0x92de_0004u32.to_le_bytes());
+        config[0x14..0x18].copy_from_slice(&0x5019u32.to_le_bytes());
+        assert_eq!(pci_bar0_address(&config), Some(0x5019_92de_0000));
+    }
+
+    #[test]
+    fn bar0_io_space_rejected() {
+        let mut config = [0u8; 0x40];
+        config[0x10..0x14].copy_from_slice(&0xefa1u32.to_le_bytes());
+        assert_eq!(pci_bar0_address(&config), None);
+    }
+
+}