[PATCH 0/5] drm/bridge: lt9611c: improve HPD handling and driver robustness

[PATCH 0/5] drm/bridge: lt9611c: improve HPD handling and driver robustness

[mohit.dsor]

From: Mohit Dsor <mohit.dsor@oss.qualcomm.com>

This series improves HPD handling and overall robustness of the
lt9611c bridge driver.

The HPD status read from the internal MCU may fail when the device
is not fully initialized, leading to spurious disconnect events.
This series mitigates such issues by falling back to a cached HPD
state and adds support for explicit HPD enable handling.

Additionally, it fixes DT parsing and bridge refcount handling,
corrects chip type initialization, and cleans up probe and remove
paths.

Tested on LT9611UXD platforms.

Signed-off-by: Mohit Dsor <mohit.dsor@oss.qualcomm.com>

Mohit Dsor (5):
  drm/bridge: lt9611c: fallback to cached HPD status on read failure
  drm/bridge: lt9611c: implement hpd_enable callback
  drm/bridge: lt9611c: fix DT parsing and bridge refcount
  drm/bridge: lt9611c: fix chip type initialization
  drm/bridge: lt9611c: clean up probe error and remove paths

 drivers/gpu/drm/bridge/lontium-lt9611c.c | 39 +++++++++++++++++++-----
 1 file changed, 32 insertions(+), 7 deletions(-)

-- 
2.34.1

[PATCH 1/5] drm/bridge: lt9611c: fallback to cached HPD status on read failure

[mohit.dsor]

From: Mohit Dsor <mohit.dsor@oss.qualcomm.com>

HPD status is retrieved via an MCU command. In some cases the
command may fail, for example when the MCU is not yet ready,
leading to incorrect disconnect reporting.

Instead of returning an error state, fall back to the last known
HPD status to provide a more stable detection result.

This avoids spurious disconnect events during initialization.

Signed-off-by: Mohit Dsor <mohit.dsor@oss.qualcomm.com>
---
 drivers/gpu/drm/bridge/lontium-lt9611c.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/lontium-lt9611c.c b/drivers/gpu/drm/bridge/lontium-lt9611c.c
index 5d67bb7391fb..81ca9d62eae3 100644
--- a/drivers/gpu/drm/bridge/lontium-lt9611c.c
+++ b/drivers/gpu/drm/bridge/lontium-lt9611c.c
@@ -711,10 +711,12 @@ lt9611c_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connector
 	guard(mutex)(&lt9611c->ocm_lock);
 
 	ret = lt9611c_read_write_flow(lt9611c, cmd, ARRAY_SIZE(cmd), data, ARRAY_SIZE(data));
-	if (ret)
+	if (ret) {
 		dev_err(dev, "failed to read HPD status (err=%d)\n", ret);
-	else
+		connected = lt9611c->hdmi_connected;
+	} else {
 		connected = (data[4] == 0x02);
+	}
 
 	lt9611c->hdmi_connected = connected;
 
-- 
2.34.1

[PATCH 2/5] drm/bridge: lt9611c: implement hpd_enable callback

[mohit.dsor]

From: Mohit Dsor <mohit.dsor@oss.qualcomm.com>

Implement the .hpd_enable callback to trigger HPD status update
and schedule event propagation.

Signed-off-by: Mohit Dsor <mohit.dsor@oss.qualcomm.com>
---
 drivers/gpu/drm/bridge/lontium-lt9611c.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/bridge/lontium-lt9611c.c b/drivers/gpu/drm/bridge/lontium-lt9611c.c
index 81ca9d62eae3..30a07e97626a 100644
--- a/drivers/gpu/drm/bridge/lontium-lt9611c.c
+++ b/drivers/gpu/drm/bridge/lontium-lt9611c.c
@@ -923,6 +923,23 @@ static void lt9611c_hdmi_audio_shutdown(struct drm_bridge *bridge,
 	drm_atomic_helper_connector_hdmi_clear_audio_infoframe(connector);
 }
 
+static void lt9611c_bridge_hpd_enable(struct drm_bridge *bridge)
+{
+	struct lt9611c *lt9611c = bridge_to_lt9611c(bridge);
+	u8 cmd[5] = {0x52, 0x48, 0x31, 0x3a, 0x00};
+	u8 data[5];
+	int ret;
+
+	mutex_lock(&lt9611c->ocm_lock);
+	ret = lt9611c_read_write_flow(lt9611c, cmd, ARRAY_SIZE(cmd),
+				      data, ARRAY_SIZE(data));
+	if (!ret)
+		lt9611c->hdmi_connected = (data[4] == 0x02);
+	mutex_unlock(&lt9611c->ocm_lock);
+
+	schedule_work(&lt9611c->work);
+}
+
 static int lt9611c_hdmi_audio_startup(struct drm_bridge *bridge,
 				      struct drm_connector *connector)
 {
@@ -939,6 +956,7 @@ static const struct drm_bridge_funcs lt9611c_bridge_funcs = {
 	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
 	.atomic_reset = drm_atomic_helper_bridge_reset,
+	.hpd_enable = lt9611c_bridge_hpd_enable,
 
 	.hdmi_tmds_char_rate_valid = lt9611c_hdmi_tmds_char_rate_valid,
 	.hdmi_write_avi_infoframe = lt9611c_hdmi_write_avi_infoframe,
-- 
2.34.1

[PATCH 3/5] drm/bridge: lt9611c: fix DT parsing and bridge refcount

[mohit.dsor]

From: Mohit Dsor <mohit.dsor@oss.qualcomm.com>

Ensure DT nodes are properly released on error and acquire a
reference to next_bridge

Signed-off-by: Mohit Dsor <mohit.dsor@oss.qualcomm.com>
---
 drivers/gpu/drm/bridge/lontium-lt9611c.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/lontium-lt9611c.c b/drivers/gpu/drm/bridge/lontium-lt9611c.c
index 30a07e97626a..4c8a3829a4be 100644
--- a/drivers/gpu/drm/bridge/lontium-lt9611c.c
+++ b/drivers/gpu/drm/bridge/lontium-lt9611c.c
@@ -974,6 +974,8 @@ static const struct drm_bridge_funcs lt9611c_bridge_funcs = {
 static int lt9611c_parse_dt(struct device *dev,
 			    struct lt9611c *lt9611c)
 {
+	int ret;
+
 	lt9611c->dsi0_node = of_graph_get_remote_node(dev->of_node, 0, -1);
 	if (!lt9611c->dsi0_node)
 		return dev_err_probe(dev, -ENODEV, "failed to get remote node for primary dsi\n");
@@ -984,7 +986,14 @@ static int lt9611c_parse_dt(struct device *dev,
 				 &lt9611c->selected_port))
 		lt9611c->selected_port = 0;
 
-	return drm_of_find_panel_or_bridge(dev->of_node, 2, -1, NULL, &lt9611c->bridge.next_bridge);
+	ret = drm_of_find_panel_or_bridge(dev->of_node, 2, -1, NULL, &lt9611c->bridge.next_bridge);
+	if (ret) {
+		of_node_put(lt9611c->dsi1_node);
+		of_node_put(lt9611c->dsi0_node);
+		return ret;
+	}
+	drm_bridge_get(lt9611c->bridge.next_bridge);
+	return 0;
 }
 
 static int lt9611c_gpio_init(struct lt9611c *lt9611c)
-- 
2.34.1

[PATCH 4/5] drm/bridge: lt9611c: fix chip type initialization

[mohit.dsor]

From: Mohit Dsor <mohit.dsor@oss.qualcomm.com>

Remove redundant assignment of chip_type from I2C match as it
is derived from DT data when available.

Signed-off-by: Mohit Dsor <mohit.dsor@oss.qualcomm.com>
---
 drivers/gpu/drm/bridge/lontium-lt9611c.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/lontium-lt9611c.c b/drivers/gpu/drm/bridge/lontium-lt9611c.c
index 4c8a3829a4be..d35a246e2d01 100644
--- a/drivers/gpu/drm/bridge/lontium-lt9611c.c
+++ b/drivers/gpu/drm/bridge/lontium-lt9611c.c
@@ -1105,7 +1105,6 @@ static int lt9611c_probe(struct i2c_client *client)
 
 	lt9611c->dev = dev;
 	lt9611c->client = client;
-	lt9611c->chip_type = id->driver_data;
 
 	if (dev->of_node) {
 		lt9611c->chip_type = (uintptr_t)of_device_get_match_data(dev);
-- 
2.34.1

[PATCH 5/5] drm/bridge: lt9611c: clean up probe error and remove paths

[mohit.dsor]

From: Mohit Dsor <mohit.dsor@oss.qualcomm.com>

Remove redundant cleanup of IRQ and bridge resources.

Signed-off-by: Mohit Dsor <mohit.dsor@oss.qualcomm.com>
---
 drivers/gpu/drm/bridge/lontium-lt9611c.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/gpu/drm/bridge/lontium-lt9611c.c b/drivers/gpu/drm/bridge/lontium-lt9611c.c
index d35a246e2d01..30828bb9b3b8 100644
--- a/drivers/gpu/drm/bridge/lontium-lt9611c.c
+++ b/drivers/gpu/drm/bridge/lontium-lt9611c.c
@@ -1234,9 +1234,7 @@ static int lt9611c_probe(struct i2c_client *client)
 	return 0;
 
 err_remove_bridge:
-	free_irq(client->irq, lt9611c);
 	cancel_work_sync(&lt9611c->work);
-	drm_bridge_remove(&lt9611c->bridge);
 
 err_disable_regulators:
 	regulator_bulk_disable(ARRAY_SIZE(lt9611c->supplies), lt9611c->supplies);
@@ -1252,7 +1250,6 @@ static void lt9611c_remove(struct i2c_client *client)
 {
 	struct lt9611c *lt9611c = i2c_get_clientdata(client);
 
-	free_irq(client->irq, lt9611c);
 	cancel_work_sync(&lt9611c->work);
 	regulator_bulk_disable(ARRAY_SIZE(lt9611c->supplies), lt9611c->supplies);
 	of_node_put(lt9611c->dsi1_node);
-- 
2.34.1

[PATCH 0/5] Subject: [PATCH 0/5] drm/bridge: lt9611c: improve HPD handling and driver robustness

[Mohit Dsor]

This series improves HPD handling and overall robustness of the
lt9611c bridge driver.

The HPD status read from the internal MCU may fail when the device
is not fully initialized, leading to spurious disconnect events.
This series mitigates such issues by falling back to a cached HPD
state and adds support for explicit HPD enable handling.

Additionally, it fixes DT parsing and bridge refcount handling,
corrects chip type initialization, and cleans up probe and remove
paths to avoid redundant or unsafe resource handling.

The changes have been validated on LT9611UXD-based platforms.

Changes in this series:
- Fallback to cached HPD status on read failures
- Add hpd_enable callback implementation
- Fix DT parsing and bridge reference counting
- Correct chip_type initialization
- Clean up probe/remove error paths

Signed-off-by: Mohit Dsor <mohit.dsor@oss.qualcomm.com>

Signed-off-by: Mohit Dsor <mohit.dsor@oss.qualcomm.com>
---
Changes in v2:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v1: https://patch.msgid.link/20260513-lt9611uxd-main-v1-1-49e4ee4eafcf@oss.qualcomm.com

To: Andrzej Hajda <andrzej.hajda@intel.com>
To: Neil Armstrong <neil.armstrong@linaro.org>
To: Robert Foss <rfoss@kernel.org>
To: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
To: Jonas Karlman <jonas@kwiboo.se>
To: Jernej Skrabec <jernej.skrabec@gmail.com>
To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
To: Maxime Ripard <mripard@kernel.org>
To: Thomas Zimmermann <tzimmermann@suse.de>
To: David Airlie <airlied@gmail.com>
To: Simona Vetter <simona@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org

---
Mohit Dsor (5):
      drm/bridge: lt9611c: fallback to cached HPD status on read failure
      drm/bridge: lt9611c: implement hpd_enable callback
      drm/bridge: lt9611c: fix DT parsing and bridge refcount
      drm/bridge: lt9611c: fix chip type initialization
      drm/bridge: lt9611c: clean up probe error and remove paths

 drivers/gpu/drm/bridge/lontium-lt9611c.c | 39 ++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 7 deletions(-)
---
base-commit: 04c2c33c284caa521524328939d67d78d581ebaf
change-id: 20260628-hpd_stable-6cee31998b8d
prerequisite-message-id: <20260508134009.4582-1-syyang@lontium.com>
prerequisite-patch-id: e9ce15b4a5842cfde130a813afecf136798179f4
prerequisite-patch-id: 569618a60e8c3615e7347c79b48c4756b7bf85d0
prerequisite-message-id: <20260611-lt9611-b4-send-v1-0-42abbcd3bb1e@oss.qualcomm.com>
prerequisite-patch-id: b73480be758c902f497733155b478248a507931c
prerequisite-patch-id: c6eb91e2966154892770cd77785eb140fa0dba5e
prerequisite-patch-id: 536e974105afdf99db85a6d117b69206fe7c50ae
prerequisite-patch-id: da212266879bd72ab2848551a5e2dda4a1ae5c90

Best regards,
--  
Mohit Dsor <mohit.dsor@oss.qualcomm.com>

[PATCH 1/5] drm/bridge: lt9611c: fallback to cached HPD status on read failure

[Mohit Dsor]

HPD status is retrieved via an MCU command. In some cases the
command may fail, for example when the MCU is not yet ready,
leading to incorrect disconnect reporting.

Instead of returning an error state, fall back to the last known
HPD status to provide a more stable detection result.

This avoids spurious disconnect events during initialization.

Signed-off-by: Mohit Dsor <mohit.dsor@oss.qualcomm.com>
---
 drivers/gpu/drm/bridge/lontium-lt9611c.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/lontium-lt9611c.c b/drivers/gpu/drm/bridge/lontium-lt9611c.c
index 5d67bb7391fb..81ca9d62eae3 100644
--- a/drivers/gpu/drm/bridge/lontium-lt9611c.c
+++ b/drivers/gpu/drm/bridge/lontium-lt9611c.c
@@ -711,10 +711,12 @@ lt9611c_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connector
 	guard(mutex)(&lt9611c->ocm_lock);
 
 	ret = lt9611c_read_write_flow(lt9611c, cmd, ARRAY_SIZE(cmd), data, ARRAY_SIZE(data));
-	if (ret)
+	if (ret) {
 		dev_err(dev, "failed to read HPD status (err=%d)\n", ret);
-	else
+		connected = lt9611c->hdmi_connected;
+	} else {
 		connected = (data[4] == 0x02);
+	}
 
 	lt9611c->hdmi_connected = connected;
 

-- 
2.34.1