Message-Id: <20250601232435.3507697-15-sashal@kernel.org>
Date: Sun,  1 Jun 2025 19:22:57 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
	stable@...r.kernel.org
Cc: Ayushi Makhija <quic_amakhija@...cinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
	Sasha Levin <sashal@...nel.org>,
	andrzej.hajda@...el.com,
	neil.armstrong@...aro.org,
	rfoss@...nel.org,
	maarten.lankhorst@...ux.intel.com,
	mripard@...nel.org,
	tzimmermann@...e.de,
	airlied@...il.com,
	simona@...ll.ch,
	lumag@...nel.org,
	dianders@...omium.org,
	nichen@...as.ac.cn,
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	xji@...logixsemi.com,
	robh@...nel.org,
	wenst@...omium.org,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 6.15 015/110] drm/bridge: anx7625: enable HPD interrupts

From: Ayushi Makhija <quic_amakhija@...cinc.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@...cinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Link: https://lore.kernel.org/r/20250505094245.2660750-4-quic_amakhija@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Signed-off-by: Sasha Levin <sashal@...nel.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,
-- 
2.39.5

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