[Intel-gfx] Request for feedback - Sprite flip notification support

[Vijay Purushothaman]

On 2/6/2014 12:28 PM, Vijay Purushothaman wrote:
> On 2/5/2014 10:18 PM, Ville Syrjälä wrote:
>> On Wed, Feb 05, 2014 at 09:25:36PM +0530, Vijay Purushothaman wrote:
>>> On 2/5/2014 8:43 PM, Ville Syrjälä wrote:
>>>> On Wed, Feb 05, 2014 at 08:35:11PM +0530, Vijay Purushothaman wrote:
>>>>> Hello,
>>>>>
>>>>> In our current driver implementation we support flip notifications
>>>>> only
>>>>> for primary plane. So, in a full screen video playback scenario where
>>>>> only one sprite plane is active, the user space is forced to rely on
>>>>> primary plane flip notification even though there is no real need for
>>>>> this plane to be active. Ideally we should be able to support flip
>>>>> notifications for any given plane. Switching off the primary plane
>>>>> (when
>>>>> not used) will help in better memory self refresh & decent power
>>>>> savings..
>>>>>
>>>>> We do have a hack in android product trees which supports flip
>>>>> notifications for one sprite plane. unfortunately this hack in its
>>>>> current form cannot be considered for up streaming...
>>>>>
>>>>> My current thinking is to have an array of unpin_work items to
>>>>> match the
>>>>> number of planes. Is anyone working on this or thought about this
>>>>> scenario in detail? Any pointers / restrictions that needs to
>>>>> considered
>>>>> for a generic implementation of this feature?
>>>>
>>>> The plan is to implement the nuclear page flip which will take care of
>>>> all planes in the same way.
>>>>
>>> Thanks Ville. If the nuclear page flip is part of your bigger atomic
>>> mode set framework, is there a way you can split this into smaller sets
>>> for merge? Multiple product trees will benefit from the nuclear page
>>> flip.
>>
>> I've split things up already somewhat. Some has landed some has not.
>>
>> Currently I have my minimal "atomic update of sprite+primary during
>> setplane" series I need to get in. It shouldn't need major work anymore,
>> just some minor tweaks. But I realized I need to limit this to just
>> pch platforms for now. Making it work reliably on gmch platforms
>> require some extra interrupt related work. The main thing here is that
>> it adds the mechanism to do the update atomically for the entire pipe.
>>
>> After that I need to post the last bits of my watermark update saga.
>> This too will initially be limited to pch platforms only. Obviously
>> watermarks need to updated correctly to avoid underruns when planes
>> get shuffled around.
>>
>>> Is there anything that i can help with? Like testing your patches with
>>> android user space?
>>
>> There's nothing to test at this point unless you want to test my old
>> branch from year ago or something.
>>
>> What needs to be done:
>> - review the latest atomic framework patches from Rob Clark
>> - expose primary/cursor planes as drm_planes
>>    * this could in theory be skipped, but it'll lead to cruft in the API
>>      we need to maintain until the end of time. Also I think restructing
>>      stuff internally to this direction will be a good idea anyway to
>> make
>>      the nuclear flip code neater. This more or less involves collecting
>>      the plane state to some plane_config type of structure, and being
>>      able to pre-compute that
>> - try to collect the necessary missing bits from my last
>>    atomic branch to implement the nuclear flip
>>    * the flip helper thing to update an arbitrary collection of planes
>>      atomically, maybe could be simplified a bit
>>    * mechanism to queue nuclear flips and make them wait for the
>>      GPU to finish writing to all the relevant buffers before issuing
>>      the actual flips/updates
>> - finally hook up the atomic ioctl to do the nuclear flip
>>    * pre-pin all buffers, pre-compute plane configs, pre-compute
>>      watermarks, check everything, wait for the GPU, and finally
>>      do the update
>>
>> For the atomic modeset side some of that's the same really. There too we
>> also need to pre-compute the plane configs and pre-pin buffers. Most of
>> the rest we already pre-compute via the pipe config. One major thing
>> left out of the pipe config pre-compute currently is PLLs. We compute
>> that stuff way too late still. We also need to massage the modeset code
>> some more to make it capable of modesetting multiple pipes at once.
>>
>
> Thanks for the detailed answer. This should solve most of the display
> issues in the product trees.. considering the amount of work involved
> this looks more like a long term solution. Would it be okay if we submit
> a short term solution for sprite flip notifications? This would help us
> to force a standard approach across multiple android product kernels. We
> can revert this fix once the atomic mode set / nuclear page flip is ready.
>
Ville / Daniel,

Ping.. Could you please suggest whether this is okay? If you think this 
is not worth or if nuclear page flip is on the horizon i will focus on 
display self refresh patches..

Thanks,
Vijay