DRM/V4L2 buffer sharing (was: Re: Patches submitted via linux-media ML that are at patchwork.linuxtv.org)

[Sylwester Nawrocki]

Hi Laurent,

On 08/15/2012 11:09 PM, Laurent Pinchart wrote:
> On Wednesday 15 August 2012 18:13:19 Sylwester Nawrocki wrote:
>> On 08/15/2012 12:06 AM, Laurent Pinchart wrote:
>>> On Tuesday 14 August 2012 18:37:23 Sylwester Nawrocki wrote:
>>>> On 08/14/2012 03:04 PM, Mauro Carvalho Chehab wrote:
>>>>> This one requires more testing:
>>>>>
>>>>> May,15 2012: [GIT,PULL,FOR,3.5] DMABUF importer feature in V4L2 API
>>>>>            http://patchwork.linuxtv.org/patch/11268  Sylwester Nawrocki
>>>>> <s.nawrocki at samsung.com>
>>>>
>>>> Hmm, this is not valid any more. Tomasz just posted a new patch series
>>>> that adds DMABUF importer and exporter feature altogether.
>>>>
>>>> [PATCHv8 00/26] Integration of videobuf2 with DMABUF
>>>>
>>>> I guess we need someone else to submit test patches for other H/W than
>>>> just Samsung SoCs. I'm not sure if we've got enough resources to port
>>>> this to other hardware. We have been using these features internally for
>>>> some time already. It's been 2 kernel releases and I can see only Ack
>>>> tags from Laurent on Tomasz's patch series, hence it seems there is no
>>>> wide interest in DMABUF support in V4L2 and this patch series is probably
>>>> going to stay in a fridge for another few kernel releases.
>>>
>>> What would be required to push it to v3.7 ?
>>
>> Mauro requested more test coverage on that, which is understood since this
>> is a fairly important API enhancement and the V4L2 video overlay API
>> replacement.
>>
>> We need DMABUF support added at some webcam driver and a DRM driver with
>> prime support (or some V4L2 output driver), I guess it would be best to
>> have that in a PC environment. It looks like i915/radeon/nouveau drivers
>> already have prime support.
> 
> uvcvideo has recently been moved to videobuf2, using vb2_vmalloc. I can easily
> test that, except that I have no idea how to export buffers on the i915 side
> when X is running. Have you looked into that ?

All right. Yes, I'm also not sure yet how to do it. I tried it on a laptop 
with i915 driver, but in the running system drmModeGetResources() just fails 
with EPERM. I've CCed dri-devel, so hopefully someone can shed some light
on this.

>> The DRM driver could be an exporter of buffers that would be passed to the
>> webcam driver.
>>
>> And except the kernel patches we would need a test application, similar
>> to that one:
>> http://git.infradead.org/users/kmpark/public-apps/blob/a7e755629a74a7ac13788
>> 2032a0f7b2480fa1490:/v4l2-drm-example/dmabuf-sharing.c
>>
>> I haven't been closely following the DMABUF APIs development, I think
>> Tomasz could provide more details on that.
>>
>> It's likely I'll get around and prepare a test case as outlined above in
>> coming days. Anyway, it would be appreciated if someone else could give this
>> patch series a try.
> 
> I've previously tested the patches on Renesas hardware, exporting buffers on
> the FBDEV side and importing them on the V4L2 side. We thus have test results
> for two different platforms, albeit all ARM-based.

I guess ARM is where those APIs will be used mostly, still it would be helpful
to have easier reproducible test environment.

--

Thanks,
Sylwester