linux-kernel - [PATCH v2 01/10] drm/connector: add mutex to protect ELD from concurrent access

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Message-Id: <20241206-drm-connector-eld-mutex-v2-1-c9bce1ee8bea@linaro.org>
Date: Fri, 06 Dec 2024 11:43:04 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Harry Wentland <harry.wentland@....com>, Leo Li <sunpeng.li@....com>, 
 Rodrigo Siqueira <Rodrigo.Siqueira@....com>, 
 Alex Deucher <alexander.deucher@....com>, 
 Christian König <christian.koenig@....com>, 
 Xinhui Pan <Xinhui.Pan@....com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Phong LE <ple@...libre.com>, Inki Dae <inki.dae@...sung.com>, 
 Seung-Woo Kim <sw0312.kim@...sung.com>, 
 Kyungmin Park <kyungmin.park@...sung.com>, 
 Krzysztof Kozlowski <krzk@...nel.org>, 
 Alim Akhtar <alim.akhtar@...sung.com>, 
 Jani Nikula <jani.nikula@...ux.intel.com>, 
 Rodrigo Vivi <rodrigo.vivi@...el.com>, 
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>, 
 Tvrtko Ursulin <tursulin@...ulin.net>, Rob Clark <robdclark@...il.com>, 
 Abhinav Kumar <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>, 
 Marijn Suijten <marijn.suijten@...ainline.org>, 
 Alain Volmat <alain.volmat@...s.st.com>, 
 Raphael Gallais-Pou <rgallaispou@...il.com>, 
 Dave Stevenson <dave.stevenson@...pberrypi.com>, 
 Maíra Canal <mcanal@...lia.com>, 
 Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 amd-gfx@...ts.freedesktop.org, linux-arm-kernel@...ts.infradead.org, 
 linux-samsung-soc@...r.kernel.org, intel-gfx@...ts.freedesktop.org, 
 intel-xe@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org, 
 freedreno@...ts.freedesktop.org
Subject: [PATCH v2 01/10] drm/connector: add mutex to protect ELD from
 concurrent access

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@...nel.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.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 fc35f47e2849ed6786d6223ac9c69e1c359fc648..bbdaaf7022b62d84594a29f1b60144920903a99a 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);
 	mutex_init(&connector->hdmi.infoframes.lock);
 	connector->edid_blob_ptr = NULL;
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 855beafb76ffbecf5c08d58e2f54bfb76f30b930..13bc4c290b17d556d654b7cdd8c48c24a32aba9c 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -5605,7 +5605,9 @@ 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;
@@ -5657,6 +5659,8 @@ 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,
@@ -5717,6 +5721,8 @@ 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 e3fa43291f449d70f3b92a00985336c4f2237bc6..1e2b25e204cb523d61d30f5409faa059bf2b86eb 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -2001,8 +2001,11 @@ 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