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 21:56:17 +0100
From:   Emil Velikov <emil.velikov@...labora.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Laszlo Ersek <lersek@...hat.com>
Cc:     Gerd Hoffmann <kraxel@...hat.com>, 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 2022/07/05, Dmitry Osipenko 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.
> 
> 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.
> 

Adding Laszlo Ersek, who debugged and tested this the last time.

Laszlo Ersek do ypu have some tips for Dmitry? Xorg seems to be
working on his end with the drm_drv_set_unique(... "pci:...") call
removed.

Original patch can be found at:
https://lore.kernel.org/dri-devel/1380526d-17fb-6eb2-0fd5-5cddbdf0a92e@collabora.com/T/#mbc1a1bedc91d1855007188a725c5c75bbc771cf0

HTH
Emil