linux-kernel - Re: [PATCH v3] media: add virtio-media driver

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Message-ID: <20250617104938.09d21b7c@foz.lan>
Date: Tue, 17 Jun 2025 10:49:38 +0200
From: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To: Alexandre Courbot <gnurou@...il.com>
Cc: Albert Esteve <aesteve@...hat.com>, "Michael S. Tsirkin"
 <mst@...hat.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil
 <hverkuil@...all.nl>, Jason Wang <jasowang@...hat.com>, Xuan Zhuo
 <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, gurchetansingh@...gle.com,
 daniel.almeida@...labora.com, adelva@...gle.com, changyeon@...gle.com,
 nicolas.dufresne@...labora.com, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org, virtualization@...ts.linux.dev
Subject: Re: [PATCH v3] media: add virtio-media driver

Hi Alex,

Em Tue, 27 May 2025 23:03:39 +0900
Alexandre Courbot <gnurou@...il.com> escreveu:

> > > > Btw, I was looking at:
> > > >
> > > >         https://github.com/chromeos/virtio-media
> > > >
> > > > (I'm assuming that this is the QEMU counterpart, right?)  
> > >
> > > crosvm actually, but QEMU support is also being worked on.  
> >
> > Do you have already QEMU patches? The best is to have the Kernel driver
> > submitted altogether with QEMU, as Kernel developers need it to do the
> > tests. In my case, I never use crosvm, and I don't have any Chromebook
> > anymore.  
> 
> IIRC Albert Esteve was working on this, maybe he can share the current status.

Any news regards to it?

> Note that crosvm does not require a Chromebook, you can build and run
> it pretty easily on a regular PC. I have put together a document to
> help with that:
> 
> https://github.com/chromeos/virtio-media/blob/main/TRY_IT_OUT.md

I started looking on it today. Already installed crossvm (I had to
install libcap-devel to build it). Still, I'm not familiar with
crossvm, which is a little be painful. In particular, how can I
enable network on it and speedup it? With suggested parameters,
it picked only one CPU, and very few memory on it:

	# cat /proc/cpuinfo|grep processor
	processor       : 0

	# free
               total        used        free      shared  buff/cache   available
	Mem:          221876       34780      139712         272       56096      187096
	Swap:              0           0           0

I'd like to be able to compile things on it and use ssh/scp. So,
the VM needs more CPUs, more memory, more network and GPU.

Btw, on a quick test with v4l2-compliance, something looks weird:
I started a camera application at the host. Still, v4l2-compliance
said successfully excecuted mmap:

Streaming ioctls:
        test read/write: OK (Not Supported)
        test blocking wait: OK
        test MMAP (no poll): OK                           
        test MMAP (select): OK                            
        Vide[2025-06-17T08:44:49.177972817+00:00 ERROR virtio_media::ioctl] VIDIOC_REQBUFS: memory type DmaBuf is currently unsupported
[2025-06-17T08:44:49.178164554+00:00 ERROR virtio_media::ioctl] VIDIOC_REQBUFS: memory type DmaBuf is currently unsupported
o Capturtest MMAP (epoll): OK                             
        test USERPTR (no poll): OK (Not Supported)
        test USERPTR (select): OK (Not Supported)
        test DMABUF (no poll): OK (Not Supported)
        test DMABUF (select): OK (Not Supported)

Which doesn't make any sense, as the host OS should not allow access
to mmap while streaming.

Thanks,
Mauro