From: Ayushi Makhija quic_amakhija@quicinc.com
[ Upstream commit ca8a78cdceb48ad3b753f836068611265840ef22 ]
When the device enters the suspend state, it prevents HPD interrupts from occurring. To address this, implement .hpd_enable() and .hpd_disable() callbacks functions of the drm_bridge.
Signed-off-by: Ayushi Makhija quic_amakhija@quicinc.com Reviewed-by: Dmitry Baryshkov dmitry.baryshkov@oss.qualcomm.com Link: https://lore.kernel.org/r/20250505094245.2660750-4-quic_amakhija@quicinc.com Signed-off-by: Dmitry Baryshkov dmitry.baryshkov@oss.qualcomm.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. ## Extensive Analysis ### **This is a User-Affecting Bug Fix, Not a Feature Addition** The commit message states this addresses a real problem: "When the device enters the suspend state, it prevents HPD interrupts from occurring." The investigation of the kernel repository reveals this fixes a significant architectural gap where the anx7625 driver: 1. **Declares HPD support** by setting `DRM_BRIDGE_OP_HPD` flag (line 2594-2595 in the driver) 2. **Fails to implement required callbacks** that the DRM bridge framework expects when this flag is set 3. **Causes unreliable external display detection** particularly during suspend/resume cycles ### **Code Changes Analysis** The implementation is extremely minimal and safe: ```c +static void anx7625_bridge_hpd_enable(struct drm_bridge *bridge) +{ + struct anx7625_data *ctx = bridge_to_anx7625(bridge); + struct device *dev = ctx->dev; + + pm_runtime_get_sync(dev); +} + +static void anx7625_bridge_hpd_disable(struct drm_bridge *bridge) +{ + struct anx7625_data *ctx = bridge_to_anx7625(bridge); + struct device *dev = ctx->dev; + + pm_runtime_put_sync(dev); +} ``` - **Only 18 lines of code added** (including function signatures and braces) - **Uses existing, well-tested PM runtime APIs** (`pm_runtime_get_sync`/`pm_runtime_put_sync`) - **No new logic or complex state management** - simply ensures power is on when HPD is enabled - **Follows established patterns** already used throughout the anx7625 driver ### **Meets All Stable Tree Criteria** 1. **✅ Important Bug Fix**: Fixes missing DRM bridge framework contract compliance that causes unreliable display detection 2. **✅ Small and Contained**: Minimal code change confined to a single driver 3. **✅ Low Regression Risk**: Uses existing PM runtime APIs with no new complex logic 4. **✅ No Architectural Changes**: Simple callback additions to existing framework 5. **✅ Subsystem Isolation**: Limited to anx7625 bridge driver, doesn't affect core kernel ### **Historical Precedent** Comparing to similar HPD-related commits: - **Similar Commit #3 (Status: YES)**: Another small anx7625 HPD fix addressing hardware timing issues - This commit follows the same pattern: small, targeted fix for real user issues ### **Real-World Impact Evidence** The kernel repository shows multiple recent commits addressing anx7625 HPD and power management issues: - Power management deadlocks affecting Chromebook external displays - Bridge suspend/resume problems - HPD detection window timing issues This commit completes the framework integration needed to prevent these classes of problems. ### **Risk Assessment** **Extremely low risk** because: - The PM runtime calls used are the same ones already extensively used in the driver - The callbacks are only invoked by the DRM bridge connector framework in well-defined contexts - No existing functionality is modified - only missing callbacks are added - Failure modes are limited to the same PM runtime error paths already handled This is a textbook example of a stable-tree-appropriate fix: small, safe, addresses real user problems, and completes missing functionality that users expect to work.
drivers/gpu/drm/bridge/analogix/anx7625.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)
diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c index 0b97b66de5774..99ef3f27ae429 100644 --- a/drivers/gpu/drm/bridge/analogix/anx7625.c +++ b/drivers/gpu/drm/bridge/analogix/anx7625.c @@ -2474,6 +2474,22 @@ static const struct drm_edid *anx7625_bridge_edid_read(struct drm_bridge *bridge return anx7625_edid_read(ctx); }
+static void anx7625_bridge_hpd_enable(struct drm_bridge *bridge) +{ + struct anx7625_data *ctx = bridge_to_anx7625(bridge); + struct device *dev = ctx->dev; + + pm_runtime_get_sync(dev); +} + +static void anx7625_bridge_hpd_disable(struct drm_bridge *bridge) +{ + struct anx7625_data *ctx = bridge_to_anx7625(bridge); + struct device *dev = ctx->dev; + + pm_runtime_put_sync(dev); +} + static const struct drm_bridge_funcs anx7625_bridge_funcs = { .attach = anx7625_bridge_attach, .detach = anx7625_bridge_detach, @@ -2487,6 +2503,8 @@ static const struct drm_bridge_funcs anx7625_bridge_funcs = { .atomic_reset = drm_atomic_helper_bridge_reset, .detect = anx7625_bridge_detect, .edid_read = anx7625_bridge_edid_read, + .hpd_enable = anx7625_bridge_hpd_enable, + .hpd_disable = anx7625_bridge_hpd_disable, };
static int anx7625_register_i2c_dummy_clients(struct anx7625_data *ctx,