[Libva] [PATCH v2 0/7] Host1x IOMMU support + VIC support

Thu Dec 15 02:52:17 UTC 2016

Hi,

Comments below:

> On Dec 14, 2016, at 6:48 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> 
> On Wed, Dec 14, 2016 at 3:11 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
>> On Wed, Dec 14, 2016 at 03:32:16PM +0200, Mikko Perttunen wrote:
>>> On 14.12.2016 15:05, Daniel Vetter wrote:
>>>> On Wed, Dec 14, 2016 at 02:41:28PM +0200, Mikko Perttunen wrote:
>>>>> On 14.12.2016 14:30, Daniel Vetter wrote:
>>>>>> On Wed, Dec 14, 2016 at 01:16:10PM +0200, Mikko Perttunen wrote:
>>>>>>> This series adds IOMMU support to Host1x and TegraDRM
>>>>>>> and adds support for the VIC (Video Image Compositor)
>>>>>>> host1x client. The series is available as a git repository at
>>>>>>> git://github.com/cyndis/linux.git; branch vic-2.
>>>>>>> 
>>>>>>> A userspace test case for VIC can be found at
>>>>>>> https://github.com/cyndis/drm/tree/work/tegra.
>>>>>>> The testcase is in tests/tegra and is called submit_vic.
>>>>>>> The testcase/TRM include full headers and documentation
>>>>>>> to program the unit. The unit by itself, however, does not
>>>>>>> readily map to existing userspace library interfaces, so
>>>>>>> implementations for those are not provided.
>>>>>> 
>>>>>> Afaik libva has an entire pile of post-processing support. Pretty sure
>>>>>> other video transcode libraries have similar interfaces, so should all be
>>>>>> possible to implement this.
>>>>> 
>>>>> We don't have any actual video transcoding support though, so unless it's
>>>>> possible to just implement a part of libva and defer the rest to some CPU
>>>>> implementation, I don't see how this is useful. I suppose I could implement
>>>>> a GStreamer plugin for colorspace conversion or resizing, since those are
>>>>> very modular.
>>>> 
>>>> Hm, I guess the question then is, how did that get enabled?
>>> 
>>> What is "that"? I'm not exactly sure.
>>> 
>>> Our architecture is such that there's the VIC that handles colorspace
>>> conversion, rescaling, blitting and can do some 2d postprocessing effects as
>>> well.
>>> 
>>> Then there's the separate NVDEC that is a video bitstream decoder. There's
>>> no support for that at the moment. I am working on the IP side of that.
>>> 
>>> The video processing pipeline is then such that NVDEC is fed the bitstream;
>>> NVDEC outputs a YUV picture in a specific format; VIC takes that YUV picture
>>> and converts/rescales it into the desired format. Or if we are encoding
>>> video, VIC takes your RGB image, converts it into a format that NVENC
>>> understands, and so on.
>>> 
>>> So with just VIC support, I could implement some simple 2D things. I don't
>>> know if anyone would want to specifically use the VIC for those since
>>> applications already have fast CPU algorithms. For the video pipeline using
>>> VIC is nice since these units can synchronize work without CPU involvement
>>> and when you're already using NVDEC or NVENC it's barely any extra effort to
>>> involve VIC as well. It can also be useful in power usage sensitive
>>> situations, but we aren't really fit for those situations with the upstream
>>> kernel anyway :)
>> 
>> Ah I thought the nvdec was already enabled, since for i915 that's how we
>> went about things (we have a pretty much exactly matching split in the
>> various video related engines). But if that's not there yet then no
>> worries, all fine.
>> 
>> Since you do seem to plan to enable everything anyway, might be worth it
>> to go directly with something like libva or libvdpau or whatever the cool
>> thing is. libva is my recommendation since it works on non-X11 too afaik,
>> but I have 0 clue. And might be worth it to check out whether you can't do
>> a super-basic libva driver that only does the post processing stuff. With
>> libva you can import/export images, so it might be possible even ... And
>> directly doing the full video engine support instead of a one-off in
>> gstreamer sounds more sensible to me.
> 
> Silly me forgot to add the experts, i.e. Sean (current libva
> maintainer) and libva mailing lists.
> -Daniel

From a purely VPP standpoint libva is something that would give VIC a readily available API in user space.  You don’t have to have a transcoding use case to leverage VPP with a surface with VA-API.  On top of that we do support DMA but import and export to provide flexibility in sharing the memory.  It’s entirely possible to support a subset of entry points (say VPP only) for VA-API through Libva and share that information in a query on the config say for your applications.  We do that all the time with various backends having feature subsets such as our hybrid Intel driver, or the IMG based PVR driver.  I believe there is also a Rock-Chip project experimenting with Libva for their media driver.

I’ll take a look at your link.

Sean

Intel, Corp.

> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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