[PATCH 1/4] drm/amd/display: Prevent vblank irq disable while VRR is active.

[Mario Kleiner]

On Mon, Mar 18, 2019 at 6:29 PM Kazlauskas, Nicholas
<Nicholas.Kazlauskas at amd.com> wrote:
>
> On 3/18/19 1:19 PM, Mario Kleiner wrote:
> > During VRR mode we can not allow vblank irq dis-/enable
> > transitions, as an enable after a disable can happen at
> > an arbitrary time during the video refresh cycle, e.g.,
> > with a high likelyhood inside vblank front-porch. An
> > enable during front-porch would cause vblank timestamp
> > updates/calculations which are completely bogus, given
> > the code can't know when the vblank will end as long
> > as we are in front-porch with no page flip completed.
> >
> > Hold a permanent vblank reference on the crtc while
> > in active VRR mode to prevent a vblank disable, and
> > drop the reference again when switching back to fixed
> > refresh rate non-VRR mode.
> >
> > Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
> > ---
> >   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 35 +++++++++++++++++++++++
> >   1 file changed, 35 insertions(+)
> >
> > 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 a718ac2..c1c3815 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > @@ -251,6 +251,12 @@ get_crtc_by_otg_inst(struct amdgpu_device *adev,
> >       return NULL;
> >   }
> >
> > +static inline bool amdgpu_dm_vrr_active(struct dm_crtc_state *dm_state)
> > +{
> > +     return dm_state->freesync_config.state == VRR_STATE_ACTIVE_VARIABLE ||
> > +            dm_state->freesync_config.state == VRR_STATE_ACTIVE_FIXED;
> > +}
> > +
> >   static void dm_pflip_high_irq(void *interrupt_params)
> >   {
> >       struct amdgpu_crtc *amdgpu_crtc;
> > @@ -4716,6 +4722,32 @@ static void update_freesync_state_on_stream(
> >                             (int)vrr_params.state);
> >   }
> >
> > +static void amdgpu_dm_handle_vrr_transition(struct dm_crtc_state *old_state,
> > +                                         struct dm_crtc_state *new_state)
> > +{
> > +     bool old_vrr_active = amdgpu_dm_vrr_active(old_state);
> > +     bool new_vrr_active = amdgpu_dm_vrr_active(new_state);
> > +
> > +     if (!old_vrr_active && new_vrr_active) {
> > +             /* Transition VRR inactive -> active:
> > +              * While VRR is active, we must not disable vblank irq, as a
> > +              * reenable after disable would compute bogus vblank/pflip
> > +              * timestamps if it likely happened inside display front-porch.
> > +              */
> > +             drm_crtc_vblank_get(new_state->base.crtc);
> > +             DRM_DEBUG_DRIVER("%s: crtc=%u VRR off->on: Get vblank ref\n",
> > +                              __func__, new_state->base.crtc->base.id);
> > +     }
> > +     else if (old_vrr_active && !new_vrr_active) {
> > +             /* Transition VRR active -> inactive:
> > +              * Allow vblank irq disable again for fixed refresh rate.
> > +              */
> > +             drm_crtc_vblank_put(new_state->base.crtc);
> > +             DRM_DEBUG_DRIVER("%s: crtc=%u VRR on->off: Drop vblank ref\n",
> > +                              __func__, new_state->base.crtc->base.id);
> > +     }
> > +}
> > +
> >   static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
> >                                   struct dc_state *dc_state,
> >                                   struct drm_device *dev,
> > @@ -4757,6 +4789,9 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
> >               goto cleanup;
> >       }
> >
> > +     /* Take care to hold extra vblank ref for a crtc in VRR mode */
> > +     amdgpu_dm_handle_vrr_transition(dm_old_crtc_state, acrtc_state);
>
> I think this forgets to drop the extra reference in the case where the
> stream is being disabled at the same time VRR is -
> amdgpu_dm_commit_planes is only called when when the stream is non-NULL.
>
> I think the logic will work if simply moved outside of the function into
> the loop that calls this.
>
> Nicholas Kazlauskas
>

Yep! v2 patch out, thanks.
-mario