Re: [virtio-dev] Re: Fwd: Qemu Support for Virtio Video V4L2 driver

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, May 11, 2020 at 01:25:23PM +0200, Dmitry Sepp wrote:
> Hi Saket,
> 
> On Montag, 11. Mai 2020 13:05:53 CEST Saket Sinha wrote:
> > Hi Keiichi,
> > 
> > I do not support the approach of  QEMU implementation forwarding
> > requests to the host's vicodec module since  this can limit the scope
> > of the virtio-video device only for testing,
> 
> That was my understanding as well.
> 
> > which instead can be used with multiple use cases such as -
> > 
> > 1. VM gets access to paravirtualized  camera devices which shares the
> > video frames input through actual HW camera attached to Host.
> 
> This use-case is out of the scope of virtio-video. Initially I had a plan to 
> support capture-only streams like camera as well, but later the decision was 
> made upstream that camera should be implemented as separate device type. We 
> still plan to implement a simple frame capture capability as a downstream 
> patch though.

You want to spec out what's in the field, spec-wise internal up/down
stream distinctions are not important.

> > 
> > 2. If Host has multiple video devices (especially in ARM SOCs over
> > MIPI interfaces or USB), different VM can be started or hotplugged
> > with selective video streams from actual HW video devices.
> 
> We do support this in our device implementation. But spec in general has no 
> requirements or instructions regarding this. And it is in fact flexible enough 
> to provide abstraction on top of several HW devices.
> 
> > 
> > Also instead of using libraries like Gstreamer in Host userspace, they
> > can also be used inside the VM userspace after getting access to
> > paravirtualized HW camera devices .
> > 
> 
> Regarding the cameras, unfortunately same as above.
> 
> Best regards,
> Dmitry.
> 
> > Regards,
> > Saket Sinha
> > 
> > On Mon, May 11, 2020 at 12:20 PM Keiichi Watanabe <keiichiw@chromium.org> 
> wrote:
> > > Hi Dmitry,
> > > 
> > > On Mon, May 11, 2020 at 6:40 PM Dmitry Sepp <dmitry.sepp@opensynergy.com> 
> wrote:
> > > > Hi Saket and all,
> > > > 
> > > > As we are working with automotive platforms, unfortunately we don't plan
> > > > any Qemu reference implementation so far.
> > > > 
> > > > Of course we are ready to support the community if any help is needed.
> > > > Is
> > > > there interest in support for the FWHT format only for testing purpose
> > > > or you want a full-featured implementation on the QEMU side?
> > > 
> > > I guess we don't need to implement the codec algorithm in QEMU.
> > > Rather, QEMU forwards virtio-video requests to the host video device
> > > or a software library such as GStreamer or ffmpeg.
> > > So, what we need to implement in QEMU is a kind of API translation,
> > > which shouldn't care about actual video formats so much.
> > > 
> > > Regarding the FWHT format discussed in the patch thread [1], in my
> > > understanding, Hans suggested to have QEMU implementation forwarding
> > > requests to the host's vicodec module [2].
> > > Then, we'll be able to test the virtio-video driver on QEMU on Linux
> > > even if the host Linux has no hardware video decoder.
> > > (Please correct me if I'm wrong.)
> > > 
> > > Let me add Hans and Linux media ML in CC.
> > > 
> > > [1]  https://patchwork.linuxtv.org/patch/61717/
> > > [2] https://lwn.net/Articles/760650/
> > > 
> > > Best regards,
> > > Keiichi
> > > 
> > > > Please note that the spec is not finalized yet and a major update is now
> > > > discussed with upstream and the Chrome OS team, which is also interested
> > > > and deeply involved in the process. The update mostly implies some
> > > > rewording and reorganization of data structures, but for sure will
> > > > require a driver rework.
> > > > 
> > > > Best regards,
> > > > Dmitry.
> > > > 
> > > > On Samstag, 9. Mai 2020 16:11:43 CEST Saket Sinha wrote:
> > > > > Hi,
> > > > > 
> > > > > As suggested on #qemu-devel IRC channel, I am including virtio-dev,
> > > > > Gerd and Michael to point in the right direction how to move forward
> > > > > with Qemu support for Virtio Video V4L2 driver
> > > > > posted in [1].
> > > > > 
> > > > > [1]: https://patchwork.linuxtv.org/patch/61717/
> > > > > 
> > > > > Regards,
> > > > > Saket Sinha
> > > > > 
> > > > > On Sat, May 9, 2020 at 1:09 AM Saket Sinha <saket.sinha89@gmail.com> 
> wrote:
> > > > > > Hi ,
> > > > > > 
> > > > > > This is to inquire about Qemu support for Virtio Video V4L2 driver
> > > > > > posted in [1].
> > > > > > I am currently not aware of any upstream effort for Qemu reference
> > > > > > implementation and would like to discuss how to proceed with the
> > > > > > same.
> > > > > > 
> > > > > > [1]: https://patchwork.linuxtv.org/patch/61717/
> > > > > > 
> > > > > > Regards,
> > > > > > Saket Sinha
> > > > 
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