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

Mon Apr 17 16:33:12 UTC 2023

On 4/17/23 11:41, Wu, Hersen wrote:
> [AMD Official Use Only - General]
> 
> Hi,
> 
> The change applies to all AMD GPU ASIC.
> Please communicate with issue reporter to see if the issue could be reproduced older ASIC, like Mendocino, CZN.

 From the community reports, it can be reproduced on as far back as the
Ryzen 4800H (which I guess is Renoir).

> 
> Thanks!
> Hersen
> 
> 
> -----Original Message-----
> From: Mahfooz, Hamza <Hamza.Mahfooz at amd.com>
> Sent: Monday, April 17, 2023 11:26 AM
> To: Koenig, Christian <Christian.Koenig at amd.com>; amd-gfx at lists.freedesktop.org
> Cc: stable at vger.kernel.org; Wentland, Harry <Harry.Wentland at amd.com>; Li, Sun peng (Leo) <Sunpeng.Li at amd.com>; Siqueira, Rodrigo <Rodrigo.Siqueira at amd.com>; Deucher, Alexander <Alexander.Deucher at amd.com>; Pan, Xinhui <Xinhui.Pan at amd.com>; David Airlie <airlied at gmail.com>; Daniel Vetter <daniel at ffwll.ch>; Pillai, Aurabindo <Aurabindo.Pillai at amd.com>; Zhuo, Qingqing (Lillian) <Qingqing.Zhuo at amd.com>; Hans de Goede <hdegoede at redhat.com>; Wu, Hersen <hersenxs.wu at amd.com>; Wang, Chao-kai (Stylon) <Stylon.Wang at amd.com>; Tuikov, Luben <Luben.Tuikov at amd.com>; dri-devel at lists.freedesktop.org; linux-kernel at vger.kernel.org
> Subject: Re: [PATCH] drm/amd/display: fix flickering caused by S/G mode
> 
> 
> On 4/17/23 11:03, Christian König wrote:
>> 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.
> 
> It seemed like it was necessary to read `tbo.resource` since the documentation for `struct ttm_buffer_object` makes mention of a "bo::resv::reserved" lock.
> 
>>
>> 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);
>>>>
>>
> --
> Hamza
-- 
Hamza