This is an ugly one unfortunately. Currently, all DRM drivers supporting atomic modesetting will save the state that userspace had set before suspending, then attempt to restore that state on resume. This probably worked very well at one point, like many other things, until DP MST came into the picture. While it's easy to restore state on normal display connectors that were disconnected during suspend regardless of their state post-resume, this can't really be done with MST because of the fact that setting up a downstream sink requires performing sideband transactions between the source and the MST hub, sending out the ACT packets, etc.

Because of this, there isn't really a guarantee that we can restore the atomic state we had before suspend once we've resumed. This sucks pretty bad, but so far I haven't run into any compositors that this actually causes serious issues with. Most compositors will notice the hotplug we send afterwards, and then reprobe state.

Since nouveau and i915 also don't fail the suspend/resume process due to failing to restore the atomic state, let's make amdgpu match this behavior. Better to resume the GPU properly, then to stop the process half way because of a potentially unavoidable atomic commit failure.

Eventually, we'll have a real fix for this problem on the DRM level. But we've got some more important low-hanging fruit to deal with first.

Signed-off-by: Lyude Paul lyude@redhat.com Cc: Jerry Zuo Jerry.Zuo@amd.com Cc: stable@vger.kernel.org # v4.15+ --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c index 3f326a2c513b..a3e65e457348 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -912,7 +912,6 @@ static int dm_resume(void *handle) struct drm_plane_state *new_plane_state; struct dm_plane_state *dm_new_plane_state; enum dc_connection_type new_connection_type = dc_connection_none; - int ret; int i;

/* power on hardware */ @@ -985,13 +984,13 @@ static int dm_resume(void *handle) } }

- ret = drm_atomic_helper_resume(ddev, dm->cached_state); + drm_atomic_helper_resume(ddev, dm->cached_state);

dm->cached_state = NULL;

amdgpu_dm_irq_resume_late(adev);

- return ret; + return 0; }

/**