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

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Date:   Wed, 6 Jul 2022 12:30:42 +0200
From:   Laszlo Ersek <lersek@...hat.com>
To:     Emil Velikov <emil.velikov@...labora.com>,
        Dmitry Osipenko <dmitry.osipenko@...labora.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

Hi Emil,

On 07/05/22 22:56, Emil Velikov wrote:
> 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

thanks for recalling this, but... I've moved to different projects, and
I'm already scraping the bottom of the barrel for every chunk of time I
can find :(

Laszlo