Questions about KMS flip

[Christian König]

Am 05.11.21 um 19:13 schrieb Daniel Vetter:
> On Thu, Nov 04, 2021 at 12:44:34PM -0400, Harry Wentland wrote:
>> +Nick
>>
>> It looks to be the old drm_plane_state->fb holds that reference. See dm_plane_helper_cleanup_fb() in amdgpu_dm.c.
> Yup plane state holds reference for its entire existing (well this holds
> in general as design principle for atomic state structs, just makes life
> easier). And the plane state is guaranteed to exist from when we first pin
> (prepare_fb plane hook) to when it's getting unpinned (cleanup_fb plane
> hook).
>
> Out of curiosity, what's blowing up?

The TTM pin count warning. What happens is that we try to free up a BO 
while it is still being pinned.

My best guess is that some DMA-buf client is doing something wrong, but 
it could of course also be that the BO was pinned for scanout.

Christian.

> -Daniel
>
>> Harry
>>
>> On 2021-11-04 08:51, Christian König wrote:
>>> Hi guys,
>>>
>>> adding the usual suspects which might know that of hand: When we do a KMS page flip, who keeps the reference to the BO while it is scanned out?
>>>
>>> We are running into warning backtraces from TTM which look more than odd.
>>>
>>> Thanks,
>>> Christian.