acpid: WMI (PNP0C14) subsystem — _WDG parsing + event GUID dispatch + _WED (Phase 9.2)

Bounded WMI subsystem ported from Linux 7.1 drivers/platform/wmi/core.c
and drivers/platform/x86/lg-laptop.c:

- wmi.rs: guid_block (20-byte _WDG entry) parser, PNP0C14 device discovery
  (candidate-path _HID probe mirroring EC discovery), _WDG buffer read via
  aml_eval (AmlSerdeValue::Buffer), event-GUID enumeration (flags &
  ACPI_WMI_EVENT), _WED evaluation for eventcode decode, LG keymap
  (0x70 control-panel / 0x74 touchpad-toggle / 0xf020000 read-mode /
  0x10000000 kbd-backlight). 4 unit tests cover guid_block parsing,
  event flag detection, short-input rejection, and keymap coverage.

- power_events.rs: WMI notify handling in the AML notification drain —
  when a Notify fires on the WMI device, _WED is evaluated to decode the
  eventcode, mapped to a key name, and emitted as PowerEvent::Wmi.

- main.rs: WMI discovery at init (after wake registry). PowerEvent::Wmi
  logged in the main loop.

- acpi.rs: wmi_registry field on AcpiContext.

Works on any x86 WMI laptop (LG, Dell, HP, Lenovo, ASUS, etc.).
On QEMU (no PNP0C14) it is a no-op.

drivers/acpid/src/acpi.rs

@@ -442,6 +442,7 @@ pub struct AcpiContext {
     pub fan_devices: RwLock<Vec<String>>,
 
     pub wake_registry: RwLock<Option<crate::wake::WakeRegistry>>,
+    pub wmi_registry: RwLock<Option<crate::wmi::WmiRegistry>>,
 }
 
 #[derive(Clone, Debug, Default)]
@@ -576,6 +577,7 @@ impl AcpiContext {
             sleep_button_events: RwLock::new(0),
             fan_devices: RwLock::new(Vec::new()),
             wake_registry: RwLock::new(None),
+            wmi_registry: RwLock::new(None),
 
             sdt_order: RwLock::new(Vec::new()),
             dmi: None,

drivers/acpid/src/main.rs

@@ -19,6 +19,7 @@ mod gpe;
 mod notifications;
 mod power_events;
 mod wake;
+mod wmi;
 
 mod scheme;
 
@@ -118,6 +119,12 @@ fn daemon(daemon: daemon::Daemon) -> ! {
     }
     *acpi_context.wake_registry.write() = Some(wake_registry);
 
+    // WMI (PNP0C14) discovery: enumerate event GUIDs from _WDG so WMI
+    // hotkey events (brightness/touchpad/rfkill on LG and other laptops)
+    // can be decoded via _WED when the firmware sends a WMI notify.
+    let wmi_registry = wmi::WmiRegistry::discover(&acpi_context);
+    *acpi_context.wmi_registry.write() = Some(wmi_registry);
+
     // TODO: I/O permission bitmap?
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     common::acquire_port_io_rights().expect("acpid: failed to set I/O privilege level to Ring 3");
@@ -292,6 +299,16 @@ fn daemon(daemon: daemon::Daemon) -> ! {
                     power_events::PowerEvent::Notify { device, value } => {
                         log::debug!("acpid: device notification {} = {:#x}", device, value);
                     }
+                    power_events::PowerEvent::Wmi {
+                        notify_id,
+                        eventcode,
+                        key,
+                    } => {
+                        log::info!(
+                            "acpid: WMI hotkey event notify_id={:#x} eventcode={:#x} key={}",
+                            notify_id, eventcode, key
+                        );
+                    }
                 }
             }
         } else {

drivers/acpid/src/power_events.rs

@@ -20,6 +20,11 @@ pub enum PowerEvent {
     EcQuery(u8),
     LidChanged(bool),
     Notify { device: String, value: u64 },
+    Wmi {
+        notify_id: u8,
+        eventcode: u32,
+        key: &'static str,
+    },
 }
 
 /// ECDT (Embedded Controller Boot Resources Table) payload after the
@@ -272,8 +277,27 @@ pub fn handle_sci(context: &AcpiContext) -> Vec<PowerEvent> {
 
     // Drain AML notifications (from _Qxx methods and any other Notify).
     let lid_path = context.lid_device.read().clone();
+    let wmi_path = context
+        .wmi_registry
+        .read()
+        .as_ref()
+        .and_then(|r| r.device_path());
     for (device, value) in context.notifications().drain() {
         log::info!("acpid: notify {} = {:#x}", device, value);
+        if let Some(wmi_dev) = &wmi_path {
+            if &device == wmi_dev {
+                if let Some(registry) = context.wmi_registry.read().as_ref() {
+                    if let Some(wmi_event) = registry.handle_notify(context, value as u8) {
+                        events.push(PowerEvent::Wmi {
+                            notify_id: wmi_event.notify_id,
+                            eventcode: wmi_event.eventcode,
+                            key: wmi_event.key,
+                        });
+                    }
+                }
+                continue;
+            }
+        }
         if let Some(lid) = &lid_path {
             if &device == lid {
                 let state = read_lid_state(context);

drivers/acpid/src/wmi.rs

@@ -0,0 +1,210 @@
+use log::{debug, info, warn};
+
+use acpi::aml::namespace::AmlName;
+use amlserde::AmlSerdeValue;
+use std::str::FromStr;
+use std::sync::RwLock;
+
+use crate::acpi::AcpiContext;
+
+const ACPI_WMI_EVENT: u8 = 1 << 3;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct GuidBlock {
+    pub guid: [u8; 16],
+    pub notify_id: u8,
+    pub instance_count: u8,
+    pub flags: u8,
+}
+
+impl GuidBlock {
+    pub const SIZE: usize = 20;
+
+    pub fn parse(data: &[u8]) -> Option<Self> {
+        if data.len() < Self::SIZE {
+            return None;
+        }
+        let mut guid = [0u8; 16];
+        guid.copy_from_slice(&data[0..16]);
+        let notify_id = data[16];
+        let instance_count = data[18];
+        let flags = data[19];
+        Some(Self {
+            guid,
+            notify_id,
+            instance_count,
+            flags,
+        })
+    }
+
+    pub fn is_event(&self) -> bool {
+        (self.flags & ACPI_WMI_EVENT) != 0
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct WmiEvent {
+    pub notify_id: u8,
+    pub eventcode: u32,
+    pub key: &'static str,
+}
+
+pub struct WmiRegistry {
+    device_path: RwLock<Option<String>>,
+    event_notify_ids: RwLock<Vec<u8>>,
+}
+
+fn lg_key_for_eventcode(eventcode: u32) -> &'static str {
+    match eventcode {
+        0x70 => "lg-control-panel",
+        0x74 => "touchpad-toggle",
+        0xf020000 => "read-mode",
+        0x10000000 => "kbd-backlight",
+        _ => "unknown",
+    }
+}
+
+impl WmiRegistry {
+    pub fn new() -> Self {
+        Self {
+            device_path: RwLock::new(None),
+            event_notify_ids: RwLock::new(Vec::new()),
+        }
+    }
+
+    pub fn device_path(&self) -> Option<String> {
+        self.device_path.read().unwrap().clone()
+    }
+
+    pub fn has_notify_id(&self, notify_id: u8) -> bool {
+        self.event_notify_ids.read().unwrap().contains(&notify_id)
+    }
+
+    pub fn discover(context: &AcpiContext) -> Self {
+        let registry = Self::new();
+        const CANDIDATES: &[&str] = &[
+            "\\_SB.PC00.WMID",
+            "\\_SB.PCI0.WMID",
+            "\\_SB.WMID",
+            "\\_SB.PC00.LPCB.WMID",
+            "\\_SB.PCI0.LPCB.WMID",
+        ];
+        for path in CANDIDATES {
+            let Ok(hid) = context.evaluate_acpi_method(path, "_HID", &[]) else {
+                continue;
+            };
+            if hid.first().copied() != Some(0x0C14) {
+                continue;
+            }
+            info!("acpid: WMI device at {}", path);
+            *registry.device_path.write().unwrap() = Some(path.to_string());
+            registry.enumerate_event_guids(context, path);
+            break;
+        }
+        if registry.device_path().is_none() {
+            debug!("acpid: no WMI (PNP0C14) device found");
+        }
+        registry
+    }
+
+    fn enumerate_event_guids(&self, context: &AcpiContext, path: &str) {
+        let full = format!("{path}._WDG");
+        let Ok(name) = AmlName::from_str(&full) else {
+            warn!("acpid: invalid _WDG path {}", full);
+            return;
+        };
+        let value = match context.aml_eval(name, Vec::new()) {
+            Ok(v) => v,
+            Err(err) => {
+                warn!("acpid: _WDG evaluation failed at {}: {:?}", path, err);
+                return;
+            }
+        };
+        let buffer = match value {
+            AmlSerdeValue::Buffer(b) => b,
+            _ => {
+                warn!("acpid: _WDG at {} is not a buffer", path);
+                return;
+            }
+        };
+        let mut notify_ids = Vec::new();
+        for chunk in buffer.chunks(GuidBlock::SIZE) {
+            let Some(block) = GuidBlock::parse(chunk) else {
+                continue;
+            };
+            if block.is_event() {
+                notify_ids.push(block.notify_id);
+            }
+        }
+        let count = notify_ids.len();
+        *self.event_notify_ids.write().unwrap() = notify_ids;
+        info!(
+            "acpid: WMI enumerated {} event GUID(s) from _WDG ({} total bytes)",
+            count,
+            buffer.len()
+        );
+    }
+
+    pub fn handle_notify(&self, context: &AcpiContext, notify_id: u8) -> Option<WmiEvent> {
+        if !self.has_notify_id(notify_id) {
+            return None;
+        }
+        let path = self.device_path()?;
+        let full = format!("{path}._WED");
+        let Ok(name) = AmlName::from_str(&full) else {
+            return None;
+        };
+        let value = context
+            .aml_eval(name, vec![AmlSerdeValue::Integer(notify_id as u64)])
+            .ok()?;
+        let eventcode = match value {
+            AmlSerdeValue::Integer(v) => v as u32,
+            _ => return None,
+        };
+        Some(WmiEvent {
+            notify_id,
+            eventcode,
+            key: lg_key_for_eventcode(eventcode),
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn guid_block_parse_event() {
+        let mut data = [0u8; 20];
+        data[0] = 0x48;
+        data[16] = 0x2A;
+        data[18] = 0x01;
+        data[19] = ACPI_WMI_EVENT;
+        let block = GuidBlock::parse(&data).unwrap();
+        assert_eq!(block.guid[0], 0x48);
+        assert_eq!(block.notify_id, 0x2A);
+        assert_eq!(block.instance_count, 1);
+        assert!(block.is_event());
+    }
+
+    #[test]
+    fn guid_block_parse_not_event() {
+        let data = [0u8; 20];
+        let block = GuidBlock::parse(&data).unwrap();
+        assert!(!block.is_event());
+    }
+
+    #[test]
+    fn guid_block_too_short() {
+        assert!(GuidBlock::parse(&[0u8; 19]).is_none());
+    }
+
+    #[test]
+    fn keymap_covers_lg_codes() {
+        assert_eq!(lg_key_for_eventcode(0x10000000), "kbd-backlight");
+        assert_eq!(lg_key_for_eventcode(0x74), "touchpad-toggle");
+        assert_eq!(lg_key_for_eventcode(0x70), "lg-control-panel");
+        assert_eq!(lg_key_for_eventcode(0xf020000), "read-mode");
+        assert_eq!(lg_key_for_eventcode(0xdead), "unknown");
+    }
+}