On 02/08/2016 02:13 AM, Mario Kleiner wrote:
Changes to drm_update_vblank_count() in Linux 4.4 broke the behaviour of the pre/post modeset functions as the new update code doesn't deal with hw vblank counter resets inbetween calls to drm_vblank_pre_modeset an drm_vblank_post_modeset, as it should. This causes mistreatment of such hw counter resets as counter wraparound, and thereby large forward jumps of the software vblank counter which in turn cause vblank event dispatching and vblank waits to fail/hang --> userspace clients hang. This symptom was reported on radeon-kms to cause a infinite hang of KDE Plasma 5 shell's login procedure, preventing users from logging in. Fix this by detecting when drm_update_vblank_count() is called inside a pre->post modeset interval. If so, clamp valid vblank increments to the safe values 0 and 1, pretty much restoring the update behavior of the old update code of Linux 4.3 and earlier. Also reset the last recorded hw vblank count at call to drm_vblank_post_modeset() to be safe against hw that after modesetting, dpms on etc. only fires its first vblank irq after drm_vblank_post_modeset() was already called. Reported-by: Vlastimil Babka <vbabka@xxxxxxx>
FWIW, I've applied the whole patchset to 4.4 and the kde5 login problem didn't occur. I can test the next version too.
Thanks, Vlastimil _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
