Re: [PATCH] drm/amd/display: fix flickering caused by S/G mode

[Hamza Mahfooz <hamza.mahfooz@xxxxxxx>]

On 4/17/23 01:59, Christian König wrote:
> Am 14.04.23 um 21:33 schrieb Hamza Mahfooz:
> > Currently, we allow the framebuffer for a given plane to move between
> > memory domains, however when that happens it causes the screen to
> > flicker, it is even possible for the framebuffer to change memory
> > domains on every plane update (causing a continuous flicker effect). So,
> > to fix this, don't perform an immediate flip in the aforementioned case.
>
> That sounds strongly like you just forget to wait for the move to finish!
>
> What is the order of things done here? E.g. who calls amdgpu_bo_pin() 
> and who waits for fences for finish signaling? Is that maybe just in the 
> wrong order?

The pinning logic is in dm_plane_helper_prepare_fb(). Also, it seems
like we wait for the fences in amdgpu_dm_atomic_commit_tail(), using
drm_atomic_helper_wait_for_fences(). The ordering should be fine as
well, since prepare_fb() is always called before atomic_commit_tail().

> Regards,
> Christian.
>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: 81d0bcf99009 ("drm/amdgpu: make display pinning more flexible 
> > (v2)")
> > Signed-off-by: Hamza Mahfooz <hamza.mahfooz@xxxxxxx>
> > ---
> >   .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 41 ++++++++++++++++++-
> >   1 file changed, 39 insertions(+), 2 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 da3045fdcb6d..9a4e7408384a 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > @@ -7897,6 +7897,34 @@ static void amdgpu_dm_commit_cursors(struct 
> > drm_atomic_state *state)
> >               amdgpu_dm_plane_handle_cursor_update(plane, 
> > old_plane_state);
> >   }
> > +static inline uint32_t get_mem_type(struct amdgpu_device *adev,
> > +                    struct drm_gem_object *obj,
> > +                    bool check_domain)
> > +{
> > +    struct amdgpu_bo *abo = gem_to_amdgpu_bo(obj);
> > +    uint32_t mem_type;
> > +
> > +    if (unlikely(amdgpu_bo_reserve(abo, true)))
> > +        return 0;
> > +
> > +    if (unlikely(dma_resv_reserve_fences(abo->tbo.base.resv, 1)))
> > +        goto err;
> > +
> > +    if (check_domain &&
> > +        amdgpu_display_supported_domains(adev, abo->flags) !=
> > +        (AMDGPU_GEM_DOMAIN_VRAM | AMDGPU_GEM_DOMAIN_GTT))
> > +        goto err;
> > +
> > +    mem_type = abo->tbo.resource->mem_type;
> > +    amdgpu_bo_unreserve(abo);
> > +
> > +    return mem_type;
> > +
> > +err:
> > +    amdgpu_bo_unreserve(abo);
> > +    return 0;
> > +}
> > +
> >   static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
> >                       struct dc_state *dc_state,
> >                       struct drm_device *dev,
> > @@ -7916,6 +7944,7 @@ static void amdgpu_dm_commit_planes(struct 
> > drm_atomic_state *state,
> >               to_dm_crtc_state(drm_atomic_get_old_crtc_state(state, 
> > pcrtc));
> >       int planes_count = 0, vpos, hpos;
> >       unsigned long flags;
> > +    uint32_t mem_type;
> >       u32 target_vblank, last_flip_vblank;
> >       bool vrr_active = amdgpu_dm_crtc_vrr_active(acrtc_state);
> >       bool cursor_update = false;
> > @@ -8035,13 +8064,21 @@ static void amdgpu_dm_commit_planes(struct 
> > drm_atomic_state *state,
> >               }
> >           }
> > +        mem_type = get_mem_type(dm->adev, old_plane_state->fb->obj[0],
> > +                    true);
> > +
> >           /*
> >            * Only allow immediate flips for fast updates that don't
> > -         * change FB pitch, DCC state, rotation or mirroing.
> > +         * change memory domain, FB pitch, DCC state, rotation or
> > +         * mirroring.
> >            */
> >           bundle->flip_addrs[planes_count].flip_immediate =
> >               crtc->state->async_flip &&
> > -            acrtc_state->update_type == UPDATE_TYPE_FAST;
> > +            acrtc_state->update_type == UPDATE_TYPE_FAST &&
> > +            (!mem_type || (mem_type && get_mem_type(dm->adev,
> > +                                fb->obj[0],
> > +                                false) ==
> > +                       mem_type));
> >           timestamp_ns = ktime_get_ns();
> >           bundle->flip_addrs[planes_count].flip_timestamp_in_us = 
> > div_u64(timestamp_ns, 1000);
--
Hamza