linux-kernel - Re: [PATCH v7 7/9] drm/virtio: Improve DMA API usage for shmem BOs

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Date:   Tue, 5 Jul 2022 14:39:54 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     Gerd Hoffmann <kraxel@...hat.com>, David Airlie <airlied@...ux.ie>,
        Robin Murphy <robin.murphy@....com>,
        Thomas Hellström <thomas_os@...pmail.org>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Dmitry Osipenko <digetx@...il.com>, kernel@...labora.com,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH v7 7/9] drm/virtio: Improve DMA API usage for shmem BOs

On Tue, Jul 5, 2022 at 10:02 AM Dmitry Osipenko
<dmitry.osipenko@...labora.com> wrote:
>
> On 7/5/22 18:45, Gerd Hoffmann wrote:
> >   Hi,
> >
> >>> Also note that pci is not the only virtio transport we have.
> >>
> >> The VirtIO indeed has other transports, but only PCI is really supported
> >> in case of the VirtIO-GPU in kernel and in Qemu/crosvm, AFAICT. Hence
> >> only the PCI transport was tested.
> >
> > qemu -M microvm \
> >   -global virtio-mmio.force-legacy=false \
> >   -device virtio-gpu-device
> >
> > Gives you a functional virtio-gpu device on virtio-mmio.
> >
> > aarch64 virt machines support both pci and mmio too.
> > s390x has virtio-gpu-ccw ...
>
> Gerd, thank you very much! It's was indeed unclear to me how to test the
> MMIO GPU, but yours variant with microvm works! I was looking for trying
> aarch64 in the past, but it also was unclear how to do it since there is
> no DT support for the VirtIO-GPU, AFAICS.

just a drive-by note, IME on aarch64 kernels, at least with crosvm,
virtgpu is also a pci device.. the non-pci things in the guest kernel
use dt, but devices on discoverable busses like pci don't need dt
nodes (which is true also in the non-vm case)

BR,
-R


> I booted kernel with this patchset applied and everything is okay, Xorg
> works.
>
>  [drm] Initialized virtio_gpu 0.1.0 0 for LNRO0005:01 on minor 0
>  virtio-mmio LNRO0005:01: [drm] drm_plane_enable_fb_damage_clips() not
> called
>  virtio-mmio LNRO0005:01: [drm] fb0: virtio_gpudrmfb frame buffer device
>
> There is no virgl support because it's a virtio-gpu-device and not
> virtio-gpu-device-gl that is PCI-only in Qemu. Hence everything seems good.
>
> I'd appreciate if you could give s390x a test.. I never touched s390x
> and it will probably take some extra effort to get into it.
>
> --
> Best regards,
> Dmitry