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 20:02:09 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     kernel@...labora.com, David Airlie <airlied@...ux.ie>,
        Thomas Hellström <thomas_os@...pmail.org>,
        Emil Velikov <emil.l.velikov@...il.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Dmitry Osipenko <digetx@...il.com>,
        virtualization@...ts.linux-foundation.org,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v7 7/9] drm/virtio: Improve DMA API usage for shmem BOs

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.

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