[PATCH AUTOSEL 6.6 03/17] drm/connector: add mutex to protect ELD from concurrent access

[Sasha Levin <sashal@kernel.org>]

From: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

[ Upstream commit df7c8e3dde37a9d81c0613285b43600f3cc70f34 ]

The connector->eld is accessed by the .get_eld() callback. This access
can collide with the drm_edid_to_eld() updating the data at the same
time. Add drm_connector.eld_mutex to protect the data from concurrenct
access. Individual drivers are not updated (to reduce possible issues
while applying the patch), maintainers are to find a best suitable way
to lock that mutex while accessing the ELD data.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241206-drm-connector-eld-mutex-v2-1-c9bce1ee8bea@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/drm_connector.c | 1 +
 drivers/gpu/drm/drm_edid.c      | 6 ++++++
 include/drm/drm_connector.h     | 5 ++++-
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 309aad5f0c808..35bed66214474 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -277,6 +277,7 @@ static int __drm_connector_init(struct drm_device *dev,
 	INIT_LIST_HEAD(&connector->probed_modes);
 	INIT_LIST_HEAD(&connector->modes);
 	mutex_init(&connector->mutex);
+	mutex_init(&connector->eld_mutex);
 	mutex_init(&connector->edid_override_mutex);
 	connector->edid_blob_ptr = NULL;
 	connector->epoch_counter = 0;
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index ee3fab115c4b5..ad872c61aac0e 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -5499,7 +5499,9 @@ EXPORT_SYMBOL(drm_edid_get_monitor_name);
 
 static void clear_eld(struct drm_connector *connector)
 {
+	mutex_lock(&connector->eld_mutex);
 	memset(connector->eld, 0, sizeof(connector->eld));
+	mutex_unlock(&connector->eld_mutex);
 
 	connector->latency_present[0] = false;
 	connector->latency_present[1] = false;
@@ -5530,6 +5532,8 @@ static void drm_edid_to_eld(struct drm_connector *connector,
 	if (!drm_edid)
 		return;
 
+	mutex_lock(&connector->eld_mutex);
+
 	mnl = get_monitor_name(drm_edid, &eld[DRM_ELD_MONITOR_NAME_STRING]);
 	drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] ELD monitor %s\n",
 		    connector->base.id, connector->name,
@@ -5590,6 +5594,8 @@ static void drm_edid_to_eld(struct drm_connector *connector,
 	drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] ELD size %d, SAD count %d\n",
 		    connector->base.id, connector->name,
 		    drm_eld_size(eld), total_sad_count);
+
+	mutex_unlock(&connector->eld_mutex);
 }
 
 static int _drm_edid_to_sad(const struct drm_edid *drm_edid,
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index d300fde6c1a47..b2e9dc02fa349 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -1764,8 +1764,11 @@ struct drm_connector {
 	struct drm_encoder *encoder;
 
 #define MAX_ELD_BYTES	128
-	/** @eld: EDID-like data, if present */
+	/** @eld: EDID-like data, if present, protected by @eld_mutex */
 	uint8_t eld[MAX_ELD_BYTES];
+	/** @eld_mutex: protection for concurrenct access to @eld */
+	struct mutex eld_mutex;
+
 	/** @latency_present: AV delay info from ELD, if found */
 	bool latency_present[2];
 	/**
-- 
2.39.5