RE: [PATCH] drm/amd/display: fix flickering caused by S/G mode
From: Wu, Hersen
Date: Mon Apr 17 2023 - 11:42:07 EST
[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.
Thanks!
Hersen
-----Original Message-----
From: Mahfooz, Hamza <Hamza.Mahfooz@xxxxxxx>
Sent: Monday, April 17, 2023 11:26 AM
To: Koenig, Christian <Christian.Koenig@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx; Wentland, Harry <Harry.Wentland@xxxxxxx>; Li, Sun peng (Leo) <Sunpeng.Li@xxxxxxx>; Siqueira, Rodrigo <Rodrigo.Siqueira@xxxxxxx>; Deucher, Alexander <Alexander.Deucher@xxxxxxx>; Pan, Xinhui <Xinhui.Pan@xxxxxxx>; David Airlie <airlied@xxxxxxxxx>; Daniel Vetter <daniel@xxxxxxxx>; Pillai, Aurabindo <Aurabindo.Pillai@xxxxxxx>; Zhuo, Qingqing (Lillian) <Qingqing.Zhuo@xxxxxxx>; Hans de Goede <hdegoede@xxxxxxxxxx>; Wu, Hersen <hersenxs.wu@xxxxxxx>; Wang, Chao-kai (Stylon) <Stylon.Wang@xxxxxxx>; Tuikov, Luben <Luben.Tuikov@xxxxxxx>; dri-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
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@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