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drm/bridge: split hpd_mutex into two mutexes

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Currently almost all bridge drivers which implement hpd_enable /
hpd_disable callbacks simply toggle the hardware registers generating
the interrupt. However, as pointed out by Jonas Karlman and Sashiko bot,
using those callbacks for enable_irq() / disable_irq() calls or
scheduling and cancelling the work can cause a AB-BA deadlock (between
hpd_mutex lock and the corresponding lock).

Split the hpd_mutex into two locks: one simply making sure that hpd_cb /
hpd_data are consistent and another one, hpd_state_mutex, making sure
that concurrent drm_bridge_hpd_enable() / drm_bridge_hpd_disable() calls
can't end up with inconsistency between hpd_cb/_data and bridge's
internal state.

Link: https://lore.kernel.org/dri-devel/9aa4bd35-bff6-4009-a959-ce31010c7b35@kwiboo.se
Link: https://sashiko.dev/#/patchset/20260513-dp-connector-hpd-v2-0-42f757bfcbf9%40oss.qualcomm.com
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://patch.msgid.link/20260528-dp-connector-hpd-v3-1-d656eb1079b7@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
This commit is contained in:
Dmitry Baryshkov
2026-05-28 10:10:48 +03:00
parent ce73a5db44
commit cd0d23939b
2 changed files with 17 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
drivers/gpu/drm/drm_bridge.c
View File

@@ -417,6 +417,7 @@ void drm_bridge_add(struct drm_bridge *bridge)
if (!list_empty(&bridge->list))
list_del_init(&bridge->list);
mutex_init(&bridge->hpd_state_mutex);
mutex_init(&bridge->hpd_mutex);
if (bridge->ops & DRM_BRIDGE_OP_HDMI)
@@ -469,6 +470,7 @@ void drm_bridge_remove(struct drm_bridge *bridge)
mutex_unlock(&bridge_lock);
mutex_destroy(&bridge->hpd_mutex);
mutex_destroy(&bridge->hpd_state_mutex);
drm_bridge_put(bridge);
}
@@ -1451,19 +1453,25 @@ void drm_bridge_hpd_enable(struct drm_bridge *bridge,
if (!(bridge->ops & DRM_BRIDGE_OP_HPD))
return;
mutex_lock(&bridge->hpd_state_mutex);
mutex_lock(&bridge->hpd_mutex);
if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n"))
if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n")) {
mutex_unlock(&bridge->hpd_mutex);
goto unlock;
}
bridge->hpd_cb = cb;
bridge->hpd_data = data;
mutex_unlock(&bridge->hpd_mutex);
if (bridge->funcs->hpd_enable)
bridge->funcs->hpd_enable(bridge);
unlock:
mutex_unlock(&bridge->hpd_mutex);
mutex_unlock(&bridge->hpd_state_mutex);
}
EXPORT_SYMBOL_GPL(drm_bridge_hpd_enable);
@@ -1484,13 +1492,15 @@ void drm_bridge_hpd_disable(struct drm_bridge *bridge)
if (!(bridge->ops & DRM_BRIDGE_OP_HPD))
return;
mutex_lock(&bridge->hpd_mutex);
mutex_lock(&bridge->hpd_state_mutex);
if (bridge->funcs->hpd_disable)
bridge->funcs->hpd_disable(bridge);
mutex_lock(&bridge->hpd_mutex);
bridge->hpd_cb = NULL;
bridge->hpd_data = NULL;
mutex_unlock(&bridge->hpd_mutex);
mutex_unlock(&bridge->hpd_state_mutex);
}
EXPORT_SYMBOL_GPL(drm_bridge_hpd_disable);

4
include/drm/drm_bridge.h
View File

@@ -1256,6 +1256,10 @@ struct drm_bridge {
* @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
*/
struct mutex hpd_mutex;
/**
* @hpd_state_mutex: Protects the HPD en/disablement state for the bridge.
*/
struct mutex hpd_state_mutex;
/**
* @hpd_cb: Hot plug detection callback, registered with
* drm_bridge_hpd_enable().