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

[Christian König]

Am 17.04.23 um 16:51 schrieb 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().

Ok, then why is there any flickering?

BTW reserving a fence slot is completely unnecessary. That looks like 
you copy&pasted the code from somewhere else without checking what it 
actually does.

Regards,
Christian.

>
>>
>> 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);
>>