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

[Hamza Mahfooz]

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 at vger.kernel.org
>> Fixes: 81d0bcf99009 ("drm/amdgpu: make display pinning more flexible 
>> (v2)")
>> Signed-off-by: Hamza Mahfooz <hamza.mahfooz at amd.com>
>> ---
>>   .../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