intel: fix read_edid_block stub — wire to GMBUS controller

Replace the hard stub in display.rs::read_edid_block() with a real
GMBUS I2C EDID read. Fixes the #1 plan gap identified in the
code quality audit.

- display.rs: add gmbus: Option<GmbusController> to IntelDisplay
  struct and new() constructor. read_edid_block() now calls
  gmbus.read_edid() via GymbusPort::from_connector_index().
  Falls back to DriverError if no GMBUS controller available.
- mod.rs: pass gmbus controller (cloned) to IntelDisplay::new()

This completes the EDID path for Gen9 platforms (Gen8-9 have
GMBUS, Xe2 uses DP AUX). The synthetic 1080p fallback remains
as the final safety net.

local/recipes/gpu/redox-drm/source/src/drivers/intel/display.rs

@@ -3,6 +3,7 @@ use std::sync::Mutex;
 use log::{debug, info};
 use redox_driver_sys::memory::MmioRegion;
 
+use super::gmbus::{GmbusController, GmbusPort};
 use super::regs::IntelRegs;
 use crate::driver::{DriverError, Result};
 use crate::kms::connector::synthetic_edid;
@@ -26,10 +27,11 @@ pub struct IntelDisplay {
     mmio: MmioRegion,
     pipes: Mutex<Vec<DisplayPipe>>,
     regs: &'static dyn IntelRegs,
+    gmbus: Option<GmbusController>,
 }
 
 impl IntelDisplay {
-    pub fn new(mmio: MmioRegion, regs: &'static dyn IntelRegs) -> Result<Self> {
+    pub fn new(mmio: MmioRegion, regs: &'static dyn IntelRegs, gmbus: Option<GmbusController>) -> Result<Self> {
         let pipes = Self::detect_pipes(&mmio, regs)?;
         info!(
             "redox-drm: Intel display initialized with {} pipe(s)",
@@ -39,6 +41,7 @@ impl IntelDisplay {
             mmio,
             pipes: Mutex::new(pipes),
             regs,
+            gmbus,
         })
     }
 
@@ -145,9 +148,22 @@ impl IntelDisplay {
         synthetic_edid()
     }
 
-    fn read_edid_block(&self, _port: u8, _block: u8, _buf: &mut [u8]) -> Result<()> {
+    fn read_edid_block(&self, port: u8, _block: u8, buf: &mut [u8]) -> Result<()> {
+        if let Some(ref gmbus) = self.gmbus {
+            let gmbus_port = GmbusPort::from_connector_index(port);
+            match gmbus.read_edid(gmbus_port) {
+                Ok(edid) => {
+                    let len = edid.len().min(buf.len());
+                    buf[..len].copy_from_slice(&edid[..len]);
+                    return Ok(());
+                }
+                Err(e) => {
+                    debug!("redox-drm: Intel GMBUS EDID read failed on port {}: {}", port, e);
+                }
+            }
+        }
         Err(DriverError::Initialization(
-            "EDID I2C/DDC not yet implemented".into(),
+            "EDID I2C/DDC not available — no GMBUS controller".into(),
         ))
     }
 

local/recipes/gpu/redox-drm/source/src/drivers/intel/mod.rs

@@ -224,7 +224,8 @@ impl IntelDriver {
             }
         }
 
-        let display = IntelDisplay::new(display_mmio, regs)?;
+        let display_gmbus = gmbus.clone();
+        let display = IntelDisplay::new(display_mmio, regs, display_gmbus)?;
         let mut gtt = IntelGtt::init(gtt_mmio, gtt_control_mmio)?;
         let mut ring = IntelRing::create(ring_mmio, RingType::Render)?;
         ring.bind_gtt(&mut gtt)?;