linux-kernel - Re: [PATCH v3 4/4] drm/virtio: Support virtgpu exported resources

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Date:   Fri, 15 May 2020 16:26:15 +0900
From:   David Stevens <stevensd@...omium.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Gerd Hoffmann <kraxel@...hat.com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jason Wang <jasowang@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        open list <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>, virtio-dev@...ts.oasis-open.org
Subject: Re: [PATCH v3 4/4] drm/virtio: Support virtgpu exported resources

> > +     if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_RESOURCE_UUID)) {
> > +             vgdev->has_resource_assign_uuid = true;
> > +     }
>
>
> Just a question: this relies on DMA bufs so I assume it is
> not really assumed to work when DMA API is bypassed, right?
> Rather than worry what does it mean, how about just
> disabling  this feature without PLATFORM_DMA for now?

By PLATFORM_DMA, do you mean CONFIG_DMA_SHARED_BUFFER? Virtio-gpu
depends on DRM, which selects that feature. So I think DMA bufs should
always be available when virtio-gpu is present.

-David