linux-kernel - [PATCH v1 2/2] drm/msm/dp: add mutex to protect internal_hpd against race condition between different threads

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Date:   Wed, 10 May 2023 13:31:05 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     <dri-devel@...ts.freedesktop.org>, <robdclark@...il.com>,
        <sean@...rly.run>, <swboyd@...omium.org>, <dianders@...omium.org>,
        <vkoul@...nel.org>, <daniel@...ll.ch>, <airlied@...il.com>,
        <agross@...nel.org>, <dmitry.baryshkov@...aro.org>,
        <andersson@...nel.org>
CC:     Kuogee Hsieh <quic_khsieh@...cinc.com>,
        <quic_abhinavk@...cinc.com>, <quic_jesszhan@...cinc.com>,
        <quic_sbillaka@...cinc.com>, <marijn.suijten@...ainline.org>,
        <freedreno@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v1 2/2] drm/msm/dp: add mutex to protect internal_hpd against race condition between different threads

Intrenal_hpd is referenced by event thread but set by drm bridge callback
context. Add mutex to protect internal_hpd to avoid conflicts between
threads.

Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
---
 drivers/gpu/drm/msm/dp/dp_display.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index 71aa944..b59ea7a 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -1792,11 +1792,13 @@ void dp_bridge_hpd_enable(struct drm_bridge *bridge)
 
 	dp = container_of(dp_display, struct dp_display_private, dp_display);
 
+	mutex_lock(&dp->event_mutex);
 	dp_display->internal_hpd = true;
 	dp_catalog_hpd_config_intr(dp->catalog,
 				DP_DP_HPD_PLUG_INT_MASK |
 				DP_DP_HPD_UNPLUG_INT_MASK,
 				true);
+	mutex_unlock(&dp->event_mutex);
 }
 
 void dp_bridge_hpd_disable(struct drm_bridge *bridge)
@@ -1807,11 +1809,13 @@ void dp_bridge_hpd_disable(struct drm_bridge *bridge)
 
 	dp = container_of(dp_display, struct dp_display_private, dp_display);
 
+	mutex_lock(&dp->event_mutex);
 	dp_catalog_hpd_config_intr(dp->catalog,
 				DP_DP_HPD_PLUG_INT_MASK |
 				DP_DP_HPD_UNPLUG_INT_MASK,
 				false);
 	dp_display->internal_hpd = false;
+	mutex_unlock(&dp->event_mutex);
 }
 
 void dp_bridge_hpd_notify(struct drm_bridge *bridge,
@@ -1822,8 +1826,12 @@ void dp_bridge_hpd_notify(struct drm_bridge *bridge,
 	struct dp_display_private *dp = container_of(dp_display, struct dp_display_private, dp_display);
 
 	/* Without next_bridge interrupts are handled by the DP core directly */
-	if (dp_display->internal_hpd)
+	mutex_lock(&dp->event_mutex);
+	if (dp_display->internal_hpd) {
+		mutex_unlock(&dp->event_mutex);
 		return;
+	}
+	mutex_unlock(&dp->event_mutex);
 
 	if (!dp->core_initialized) {
 		drm_dbg_dp(dp->drm_dev, "not initialized\n");
-- 
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