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 17:27:35 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     David Airlie <airlied@...ux.ie>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Thomas Hellström <thomas_os@...pmail.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Dmitry Osipenko <digetx@...il.com>, kernel@...labora.com
Subject: Re: [PATCH v7 7/9] drm/virtio: Improve DMA API usage for shmem BOs

Hello Gerd,

On 7/5/22 16:53, Gerd Hoffmann wrote:
>   Hi,
> 
>> -	 * So for the moment keep things as-is, with a bulky comment
>> -	 * for the next person who feels like removing this
>> -	 * drm_dev_set_unique() quirk.
> 
> Dragons lurking here.  It's not the first attempt to ditch this, and so
> far all have been rolled back due to regressions.  Specifically Xorg is
> notoriously picky if it doesn't find its expectations fulfilled.

I saw the previous attempt. Back then it was a mechanically created
patch that didn't get any testing.

> 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.

> What kind of testing has this patch seen?

The Xorg and virgl work perfectly fine in Qemu (with and without IOMMU
enabled in Qemu) and in crosvm (ChromeOS virtual machine).

-- 
Best regards,
Dmitry