On Fri, Feb 12, 2016 at 08:30:32PM +0100, Mario Kleiner wrote:
> In the display resume path, move the calls to drm_vblank_on()
> after the point when the display engine is running again.
>
> Since changes were made to drm_update_vblank_count() in Linux 4.4+
> to emulate hw vblank counters via vblank timestamping, the function
> drm_vblank_on() now needs working high precision vblank timestamping
> and therefore working scanout position queries at time of call.
> These don't work before the display engine gets restarted, causing
> miscalculation of vblank counter increments and thereby large forward
> jumps in vblank count at display resume. These jumps can cause client
> hangs on resume, or desktop hangs in the case of composited desktops.
>
> Fix this Linux 4.4 regression by reordering calls accordingly.
>
> Signed-off-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.4+
> Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
> Cc: ville.syrjala@xxxxxxxxxxxxxxx
> Cc: daniel.vetter@xxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> ---
> drivers/gpu/drm/nouveau/nouveau_display.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_display.c b/drivers/gpu/drm/nouveau/nouveau_display.c
> index 18676b8..1f8e51b 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_display.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_display.c
> @@ -634,10 +634,6 @@ nouveau_display_resume(struct drm_device *dev, bool runtime)
> nv_crtc->lut.depth = 0;
> }
>
> - /* Make sure that drm and hw vblank irqs get resumed if needed. */
> - for (head = 0; head < dev->mode_config.num_crtc; head++)
> - drm_vblank_on(dev, head);
> -
> /* This should ensure we don't hit a locking problem when someone
> * wakes us up via a connector. We should never go into suspend
> * while the display is on anyways.
> @@ -647,6 +643,10 @@ nouveau_display_resume(struct drm_device *dev, bool runtime)
>
> drm_helper_resume_force_mode(dev);
>
> + /* Make sure that drm and hw vblank irqs get resumed if needed. */
> + for (head = 0; head < dev->mode_config.num_crtc; head++)
> + drm_vblank_on(dev, head);
Hm, imo correct place for these is in the crtc->enable/disable hooks, but
those are only guaranteed to be called symmetrically on atomic drivers.
Anyway as an interim fix this looks good.
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> +
> list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
> struct nouveau_crtc *nv_crtc = nouveau_crtc(crtc);
>
> --
> 1.9.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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