Re: [PATCH v2 0/1] VirtIO video device specification

[Keiichi Watanabe <keiichiw@chromium.org>]

Hi Dmitry,

On Sat, Dec 21, 2019 at 12:59 AM Dmitry Sepp
<dmitry.sepp@opensynergy.com> wrote:
>
> Hi Keiichi,
>
> On Mittwoch, 18. Dezember 2019 14:02:13 CET Keiichi Watanabe wrote:
> > Hi,
> > This is the 2nd version of virtio-video patch. The PDF is available in [1].
> > The first version was sent at [2].
> >
> > Any feedback would be appreciated. Thank you.
> >
> > Best,
> > Keiichi
> >
> > [1]:
> > https://drive.google.com/drive/folders/1eT5fEckBoor2iHZR4f4GLxYzFMVapOFx?us
> > p=sharing [2]: https://markmail.org/message/gc6h25acct22niut
> >
> > Change log:
> >
> > v2:
> > * Removed functionalities except encoding and decoding.
> > * Splited encoder and decoder into different devices that use the same
> > protocol. * Replaced GET_FUNCS with GET_CAPABILITY.
> > * Updated structs for capabilities.
> >   - Defined new structs and enums such as image formats, profiles, range
> > (min, max, step), etc
> >     * For virtio_video_pixel_format, chose a naming convention that is used
> >       in DRM. We removed XBGR, NV21 and I422, as they are not used in the
> >       current draft implementation. https://lwn.net/Articles/806416/
> >   - Removed virtio_video_control, whose usage was not documented yet and
> > which is not necessary for the simplest decoding scenario.
> >   - Removed virtio_video_desc, as it is no longer needed.
> > * Updated struct virtio_video_config for changes around capabilities.
> > * Added a way to represent supported combinations of formats.
> >   - A field "mask" in virtio_video_format_desc plays this role.
> > * Removed VIRTIO_VIDEO_T_STREAM_{START,STOP} because they don't play any
> > meaningful roles. * Removed VIRTIO_VIDEO_T_STREAM_{ATTACH, DETACH}_BACKING
> > and merged them into RESOURCE_{CREATE, DESTROY}. * Added a way to
> > notify/specify resource creation method.
> >   - Added a feature flag.
> >   - Defined enum virtio_video_mem_type.
> >   - Added new fields in video_stream_create.
> > * Modified fields in virtio_video_params.
> >   - Added crop information.
> > * Removed enum virtio_video_channel_type because we can get this information
> > by image format.
> Could you please explain this? How do you get the information?

It means that if image formats are well-defined, channel information
(e.g. the order of channels) is uniquely determined.

>
> Suppose you have some piece of HW on the host side that wants I420 as one
> contig buffer w/ some offsets. But on the driver side, say, gralloc gives you
> three separate buffers, one per channel. How do we pass those to the device
> then?

You're talking about CrOS use case where buffers are allocated by
virtio-gpu, right?
In this case, virtio-gpu allocates one contiguous host-side buffer and
the client regards a pair of (buffer FD, offset) as one channel.
And, we can register this pair to the device when the buffer is imported.
In the virtio-vdec spec draft, this pair corresponds to struct
virtio_vdec_plane in struct virtio_vdec_plane.

So, I suppose we will need similar structs when we add a control to
import buffers. However, I don't think it's necessary when guest pages
are used.

Best regards,
Keiichi


>
> Best regards,
> Dmitry.
>
> > * Renamed virtio_video_pin to virtio_video_buf_type.
> >   - It's similar to V4L2_BUF_TYPE_VIDEO_{OUTPUT, CAPTURE}.
> > * Added an error event.
> > * Reordered some subsections.
> > * Changed styles to make it consistent with other devices.
> >
> > Dmitry Sepp (1):
> >   virtio-video: Add virtio video device specification
> >
> >  content.tex      |   1 +
> >  virtio-video.tex | 579 +++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 580 insertions(+)
> >  create mode 100644 virtio-video.tex
> >
> > --
> > 2.24.1.735.g03f4e72817-goog
>
>