Questions about KMS flip

[Christian König]

Am 16.11.21 um 04:27 schrieb Lang Yu:
> On Mon, Nov 15, 2021 at 01:04:15PM +0100, Michel DDDnzer wrote:
>> [SNIP]
>>> Though a single call to dce_v*_0_crtc_do_set_base() will
>>> only pin the BO, I found it will be unpinned in next call to
>>> dce_v*_0_crtc_do_set_base().
>> Yeah, that's the normal case when the new BO is different from the old one.
>>
>> To catch the case I described, try something like
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c b/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c
>>
>> index 18a7b3bd633b..5726bd87a355 100644
>>
>> --- a/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c
>>
>> +++ b/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c
>>
>> @@ -1926,6 +1926,7 @@ static int dce_v11_0_crtc_do_set_base(struct drm_crtc *crtc,
>>
>>                  return r;
>>
>>
>>
>>          if (!atomic) {
>>
>> +               WARN_ON_ONCE(target_fb == fb);
>>
>>                  r = amdgpu_bo_pin(abo, AMDGPU_GEM_DOMAIN_VRAM);
>>
>>                  if (unlikely(r != 0)) {
>>
>>                          amdgpu_bo_unreserve(abo);
>>
> I did some tests, the warning can be triggered.
>
> pin/unpin operations in *_crtc_do_set_base() and
> amdgpu_display_crtc_page_flip_target() are mixed.

Ok sounds like we narrowed down the root cause pretty well.

Question is now how can we fix this? Just not pin the BO when target_fb 
== fb?

Thanks,
Christian.

>
> Regards,
> Lang
>