[Intel-gfx] [PATCH 4/6] drm/i915: Allow mmio updates on all platforms.

[Maarten Lankhorst]

Op 24-03-16 om 15:48 schreef Ville Syrjälä:
> On Thu, Mar 24, 2016 at 03:42:28PM +0100, Maarten Lankhorst wrote:
>> Op 24-03-16 om 15:26 schreef Ville Syrjälä:
>>> On Thu, Mar 24, 2016 at 09:35:04AM +0100, Maarten Lankhorst wrote:
>>>> Op 23-03-16 om 16:07 schreef Ville Syrjälä:
>>>>> On Wed, Mar 23, 2016 at 02:24:30PM +0100, Maarten Lankhorst wrote:
>>>>>> Rename intel_unpin_work to intel_flip_work and use it for mmio flips
>>>>>> and unpinning. Use flip_queued_req to hold the wait request in the
>>>>>> mmio case and allow the vblank interrupt to complete mmio work to
>>>>>> have mmio flips run correctly on g4 and earlier.
>>>>> Before you actually go and trust drm_vblank_count() you should make it
>>>>> race free.
>>>> How about adding the below to the patch?
>>> You can't just mix the hw and sw counter. Using the hw counter would be
>>> neat because it doesn't require so much work to be race-free, but that
>>> leaves out gen2 which I don't like. My atomic code used the hw counter
>>> though, but I had plans to fall back to the sw counter on gen2
>>> eventually.
>>>
>> So I dug in a little bit more..
>>
>> MMIO updates don't require accurate vblank count for anything, so even if it was completely removed it would work.
> Yes they do if you want to use the vblank irq for completing them.
>
Why? We only need a vblank irq, after the mmio updates are done we set an atomic that indicates mmio is done, which is checked in the vblank irq.