Re: [Intel-gfx] [Intel-xe] [PATCH] drm/xe/display: Do not use i915 frontbuffer tracking implementation

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Hey,


On 2023-03-08 14:36, Ville Syrjälä wrote:
> On Wed, Mar 08, 2023 at 01:47:12PM +0100, Maarten Lankhorst wrote:
>> On 2023-03-06 21:58, Ville Syrjälä wrote:
>>> On Mon, Mar 06, 2023 at 09:23:50PM +0100, Maarten Lankhorst wrote:
>>>> Hey,
>>>>
>>>> On 2023-03-06 16:23, Souza, Jose wrote:
>>>>> On Mon, 2023-03-06 at 15:16 +0100, Maarten Lankhorst wrote:
>>>>>> As a fallback if we decide not to merge the frontbuffer tracking, allow
>>>>>> i915 to keep its own implementation, and do the right thing in Xe.
>>>>>>
>>>>>> The frontbuffer tracking for Xe is still done per-fb, while i915 can
>>>>>> keep doing the weird intel_frontbuffer + i915_active thing without
>>>>>> blocking Xe.
>>>>> Please also disable PSR and FBC with this or at least add a way for users to disable those features.
>>>>> Without frontbuffer tracker those two features will break in some cases.
>>>> FBC and PSR work completely as expected. I don't remove frontbuffer
>>>> tracking; I only remove the GEM parts.
>>>>
>>>> Explicit invalidation using pageflip or CPU rendering + DirtyFB continue
>>>> to work, as I validated on my laptop with FBC.
>>> Neither of which are relevant to the removal of the gem hooks.
>>>
>>> Like I already said ~10 times in the last meeting, we need a proper
>>> testcase. Here's a rough idea what it should do:
>>>
>>> prepare a batch with
>>> 1. spinner
>>> 2. something that clobbers the fb
>>>
>>> Then
>>> 1. grab reference crc
>>> 2. execbuffer
>>> 3. dirtyfb
>>> 4. wait long enough for fbc to recompress
>>> 5. terminate spinner
>>> 6. gem_sync
>>> 7. grab crc and compare with reference
>>>
>>> No idea what the current status of PSR+CRC is, so not sure
>>> whether we can actually test PSR or not.
>> This test doesn't make sense. DirtyFB should simply not return before
>> execbuffer finishes.
> Of course it should. It's not a blocking ioctl, and can't
> be because that will make X unusable.

Except it actually is.

DirtyFB blocks in its default implementation, and waits for the next vblank.

drm_atomic_helper_dirtyfb() blocks by default as it's a synchronous 
plane update.

Considering every driver except i915 uses it, it works just fine. :)

~Maarten