You signed in with another tab or window. Reload to refresh your session.You signed out in another tab or window. Reload to refresh your session.You switched accounts on another tab or window. Reload to refresh your session.Dismiss alert
Currently the way that we prevent userspace from performing new modesets
on MST connectors that have just been destroyed is rather broken.
There's nothing in the actual DRM DP MST topology helpers that checks
whether or not a connector still exists, instead each DRM driver does
this on it's own, usually by returning NULL from the best_encoder
callback which in turn, causes the atomic commit to fail.
However, this is wrong in a rather subtle way. If ->best_encoder()
returns NULL, this makes ALL modesets involving the connector fail. This
includes modesets from userspace that would shut off the CRTCs being
used by the connector. Since this results in blocking any changes to a
connector's DPMS prop, it has the sideaffect of preventing legacy
modesetting users from ever disabling a CRTC that was previously enabled
for use in an MST topology. An example of this, where X tries to
change the DPMS property of an MST connector that was just detached from
the system:
[ 2908.320131] [drm:drm_helper_probe_single_connector_modes [drm_kms_helper]] [CONNECTOR:82:DP-6]
[ 2908.320148] [drm:drm_helper_probe_single_connector_modes [drm_kms_helper]] [CONNECTOR:82:DP-6] status updated from connected to disconnected
[ 2908.320166] [drm:drm_helper_probe_single_connector_modes [drm_kms_helper]] [CONNECTOR:82:DP-6] disconnected
[ 2908.320193] [drm:drm_mode_object_put.part.2 [drm]] OBJ ID: 111 (1)
[ 2908.320230] [drm:drm_sysfs_hotplug_event [drm]] generating hotplug event
...
[ 2908.638539] [drm:drm_ioctl [drm]] pid=12928, dev=0xe201, auth=1, DRM_IOCTL_MODE_SETPROPERTY
[ 2908.638546] [drm:drm_atomic_state_init [drm]] Allocated atomic state 000000007155ba49
[ 2908.638553] [drm:drm_mode_object_get [drm]] OBJ ID: 114 (1)
[ 2908.638560] [drm:drm_mode_object_get [drm]] OBJ ID: 108 (1)
[ 2908.638568] [drm:drm_atomic_get_crtc_state [drm]] Added [CRTC:41:head-0] 0000000097a6396e state to 000000007155ba49
[ 2908.638575] [drm:drm_atomic_add_affected_connectors [drm]] Adding all current connectors for [CRTC:41:head-0] to 000000007155ba49
[ 2908.638582] [drm:drm_mode_object_get [drm]] OBJ ID: 82 (3)
[ 2908.638589] [drm:drm_mode_object_get [drm]] OBJ ID: 82 (4)
[ 2908.638596] [drm:drm_atomic_get_connector_state [drm]] Added [CONNECTOR:82:DP-6] 0000000087427144 state to 000000007155ba49
[ 2908.638603] [drm:drm_atomic_check_only [drm]] checking 000000007155ba49
[ 2908.638609] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]] [CRTC:41:head-0] active changed
[ 2908.638613] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]] Updating routing for [CONNECTOR:82:DP-6]
[ 2908.638616] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]] No suitable encoder found for [CONNECTOR:82:DP-6]
[ 2908.638623] [drm:drm_atomic_check_only [drm]] atomic driver check for 000000007155ba49 failed: -22
[ 2908.638630] [drm:drm_atomic_state_default_clear [drm]] Clearing atomic state 000000007155ba49
[ 2908.638637] [drm:drm_mode_object_put.part.2 [drm]] OBJ ID: 82 (4)
[ 2908.638643] [drm:drm_mode_object_put.part.2 [drm]] OBJ ID: 82 (3)
[ 2908.638650] [drm:drm_mode_object_put.part.2 [drm]] OBJ ID: 114 (2)
[ 2908.638656] [drm:drm_mode_object_put.part.2 [drm]] OBJ ID: 108 (2)
[ 2908.638663] [drm:__drm_atomic_state_free [drm]] Freeing atomic state 000000007155ba49
[ 2908.638669] [drm:drm_mode_object_put.part.2 [drm]] OBJ ID: 82 (2)
[ 2908.638676] [drm:drm_ioctl [drm]] pid=12928, ret = -22
While this doesn't usually result in any errors that would be obvious to
the user, it does result in us leaving display resources on. This in
turn leads to unwanted sideaffects like inactive GPUs being left on
(usually from the resulting leaked runtime PM ref).
So, provide an easier way of doing this that doesn't require breaking
->best_encoder(): add a common drm_dp_mst_connector_atomic_check()
function that DRM drivers can call in order to have CRTC enabling
commits fail automatically if the MST port driving the connector no
longer exists. We'll also be able to expand upon this later as well once
we add MST fallback retraining support.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: stable@vger.kernel.org
0 commit comments