• Mario Kleiner's avatar
    drm: Fix drm_vblank_pre/post_modeset regression from Linux 4.4 · 439c9942
    Mario Kleiner authored
    commit c61934ed upstream.
    
    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: default avatarVlastimil Babka <vbabka@suse.cz>
    Signed-off-by: default avatarMario Kleiner <mario.kleiner.de@gmail.com>
    Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    Tested-by: default avatarVlastimil Babka <vbabka@suse.cz>
    Cc: michel@daenzer.net
    Cc: vbabka@suse.cz
    Cc: ville.syrjala@linux.intel.com
    Cc: daniel.vetter@ffwll.ch
    Cc: dri-devel@lists.freedesktop.org
    Cc: alexander.deucher@amd.com
    Cc: christian.koenig@amd.com
    Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    439c9942
drm_irq.c 58.2 KB