linux-kernel - [PATCH] drm/msm/dp: add fail safe mode outside of event

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Date:   Thu, 7 Apr 2022 09:51:26 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     <robdclark@...il.com>, <sean@...rly.run>, <swboyd@...omium.org>,
        <vkoul@...nel.org>, <daniel@...ll.ch>, <airlied@...ux.ie>,
        <agross@...nel.org>, <dmitry.baryshkov@...aro.org>,
        <bjorn.andersson@...aro.org>
CC:     <quic_abhinavk@...cinc.com>, <quic_aravindh@...cinc.com>,
        <quic_khsieh@...cinc.com>, <quic_sbillaka@...cinc.com>,
        <freedreno@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] drm/msm/dp: add fail safe mode outside of event_mutex context

There is possible circular locking dependency detected on event_mutex.
To break this possible circular locking, this patch move setting fail
safe mode out of event_mutex scope.

Fixes: d4aca422539c ("drm/msm/dp:  always add fail-safe mode into connector mode list")
Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
---
 drivers/gpu/drm/msm/dp/dp_display.c |  6 ++++++
 drivers/gpu/drm/msm/dp/dp_panel.c   | 20 ++++++++++----------
 drivers/gpu/drm/msm/dp/dp_panel.h   |  1 +
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index 178b774..a42732b 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -580,6 +580,12 @@ static int dp_hpd_plug_handle(struct dp_display_private *dp, u32 data)
 			dp->dp_display.connector_type, state);
 	mutex_unlock(&dp->event_mutex);
 
+	/*
+	 * add fail safe mode outside event_mutex scope
+	 * to avoid potiential circular lock with drm thread
+	 */
+	dp_panel_add_fail_safe_mode(dp->dp_display.connector);
+
 	/* uevent will complete connection part */
 	return 0;
 };
diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c
index f141872..26c3653 100644
--- a/drivers/gpu/drm/msm/dp/dp_panel.c
+++ b/drivers/gpu/drm/msm/dp/dp_panel.c
@@ -151,6 +151,15 @@ static int dp_panel_update_modes(struct drm_connector *connector,
 	return rc;
 }
 
+void dp_panel_add_fail_safe_mode(struct drm_connector *connector)
+{
+	/* fail safe edid */
+	mutex_lock(&connector->dev->mode_config.mutex);
+	if (drm_add_modes_noedid(connector, 640, 480))
+		drm_set_preferred_mode(connector, 640, 480);
+	mutex_unlock(&connector->dev->mode_config.mutex);
+}
+
 int dp_panel_read_sink_caps(struct dp_panel *dp_panel,
 	struct drm_connector *connector)
 {
@@ -207,16 +216,7 @@ int dp_panel_read_sink_caps(struct dp_panel *dp_panel,
 			goto end;
 		}
 
-		/* fail safe edid */
-		mutex_lock(&connector->dev->mode_config.mutex);
-		if (drm_add_modes_noedid(connector, 640, 480))
-			drm_set_preferred_mode(connector, 640, 480);
-		mutex_unlock(&connector->dev->mode_config.mutex);
-	} else {
-		/* always add fail-safe mode as backup mode */
-		mutex_lock(&connector->dev->mode_config.mutex);
-		drm_add_modes_noedid(connector, 640, 480);
-		mutex_unlock(&connector->dev->mode_config.mutex);
+		dp_panel_add_fail_safe_mode(connector);
 	}
 
 	if (panel->aux_cfg_update_done) {
diff --git a/drivers/gpu/drm/msm/dp/dp_panel.h b/drivers/gpu/drm/msm/dp/dp_panel.h
index 9023e5b..99739ea 100644
--- a/drivers/gpu/drm/msm/dp/dp_panel.h
+++ b/drivers/gpu/drm/msm/dp/dp_panel.h
@@ -59,6 +59,7 @@ int dp_panel_init_panel_info(struct dp_panel *dp_panel);
 int dp_panel_deinit(struct dp_panel *dp_panel);
 int dp_panel_timing_cfg(struct dp_panel *dp_panel);
 void dp_panel_dump_regs(struct dp_panel *dp_panel);
+void dp_panel_add_fail_safe_mode(struct drm_connector *connector);
 int dp_panel_read_sink_caps(struct dp_panel *dp_panel,
 		struct drm_connector *connector);
 u32 dp_panel_get_mode_bpp(struct dp_panel *dp_panel, u32 mode_max_bpp,
-- 
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