This is a note to let you know that I've just added the patch titled
gpu: drm_dp_cec: fix broken CEC adapter properties check
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
gpu-drm_dp_cec-fix-broken-cec-adapter-properties-che.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 577594bca75ad9d11755452a1f43457d5d1d3de3
Author: Hans Verkuil <hverkuil@xxxxxxxxx>
Date: Wed Jan 29 10:51:48 2025 +0100
gpu: drm_dp_cec: fix broken CEC adapter properties check
[ Upstream commit 6daaae5ff7f3b23a2dacc9c387ff3d4f95b67cad ]
If the hotplug detect of a display is low for longer than one second
(configurable through drm_dp_cec_unregister_delay), then the CEC adapter
is unregistered since we assume the display was disconnected. If the
HPD went low for less than one second, then we check if the properties
of the CEC adapter have changed, since that indicates that we actually
switch to new hardware and we have to unregister the old CEC device and
register a new one.
Unfortunately, the test for changed properties was written poorly, and
after a new CEC capability was added to the CEC core code the test always
returned true (i.e. the properties had changed).
As a result the CEC device was unregistered and re-registered for every
HPD toggle. If the CEC remote controller integration was also enabled
(CONFIG_MEDIA_CEC_RC was set), then the corresponding input device was
also unregistered and re-registered. As a result the input device in
/sys would keep incrementing its number, e.g.:
/sys/devices/pci0000:00/0000:00:08.1/0000:e7:00.0/rc/rc0/input20
Since short HPD toggles are common, the number could over time get into
the thousands.
While not a serious issue (i.e. nothing crashes), it is not intended
to work that way.
This patch changes the test so that it only checks for the single CEC
capability that can actually change, and it ignores any other
capabilities, so this is now safe as well if new caps are added in
the future.
With the changed test the bit under #ifndef CONFIG_MEDIA_CEC_RC can be
dropped as well, so that's a nice cleanup.
Signed-off-by: Hans Verkuil <hverkuil@xxxxxxxxx>
Reported-by: Farblos <farblos@xxxxxxxxxxxxxxx>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
Fixes: 2c6d1fffa1d9 ("drm: add support for DisplayPort CEC-Tunneling-over-AUX")
Tested-by: Farblos <farblos@xxxxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/361bb03d-1691-4e23-84da-0861ead5dbdc@xxxxxxxxx
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/gpu/drm/display/drm_dp_cec.c b/drivers/gpu/drm/display/drm_dp_cec.c
index ae39dc7941903..868bf53db66ce 100644
--- a/drivers/gpu/drm/display/drm_dp_cec.c
+++ b/drivers/gpu/drm/display/drm_dp_cec.c
@@ -310,16 +310,6 @@ void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
if (!aux->transfer)
return;
-#ifndef CONFIG_MEDIA_CEC_RC
- /*
- * CEC_CAP_RC is part of CEC_CAP_DEFAULTS, but it is stripped by
- * cec_allocate_adapter() if CONFIG_MEDIA_CEC_RC is undefined.
- *
- * Do this here as well to ensure the tests against cec_caps are
- * correct.
- */
- cec_caps &= ~CEC_CAP_RC;
-#endif
cancel_delayed_work_sync(&aux->cec.unregister_work);
mutex_lock(&aux->cec.lock);
@@ -336,7 +326,9 @@ void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
num_las = CEC_MAX_LOG_ADDRS;
if (aux->cec.adap) {
- if (aux->cec.adap->capabilities == cec_caps &&
+ /* Check if the adapter properties have changed */
+ if ((aux->cec.adap->capabilities & CEC_CAP_MONITOR_ALL) ==
+ (cec_caps & CEC_CAP_MONITOR_ALL) &&
aux->cec.adap->available_log_addrs == num_las) {
/* Unchanged, so just set the phys addr */
cec_s_phys_addr_from_edid(aux->cec.adap, edid);
