[PATCH] drm/amd/display: Add fast path for cursor plane updates

[Nicholas Kazlauskas]

On 2018-12-06 10:36 a.m., Grodzovsky, Andrey wrote:
> Not an expert on Freesync so maybe stupid question but from he comment
> looks like this pipe locking is only for the sake of Freesync mode there
> - why is it then called unconditionally w/o checking if you even run in
> Freesync mode ?
> 
> Andrey
I don't think there's any sort of state tracking done in DC for FreeSync 
state changes on a stream so it was probably easier to do this. Given 
the age of the pipe lock addition I would be worried about other 
behavior relying on it now if it was just conditionally done on that.

In practice I think the worst case effect of guarding these calls with a 
mutex is <100us of delay. That's for two separate threads issuing two 
commits at the same time with the planes changed.

Nicholas Kazlauskas

> 
> 
> On 12/06/2018 08:42 AM, Kazlauskas, Nicholas wrote:
>> A reader/writer lock wouldn't help here, actually.
>>
>> Fast updates (and page flips in particular) need to lock the pipe as
>> well, see: commit_planes_for_stream.
>>
>> Nicholas Kazlauskas
>