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

[Daniel Vetter]

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.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch