> -----Original Message-----
> From: dri-devel <[email protected]> On Behalf Of Gerd
> Hoffmann
> Sent: Friday, February 12, 2021 7:02 PM
> To: Kasireddy, Vivek <[email protected]>
> Cc: Kim, Dongwon <[email protected]>; [email protected];
> [email protected]; [email protected];
> [email protected]; Vetter, Daniel
> <[email protected]>; [email protected]
> Subject: Re: [RFC v3 2/3] virtio: Introduce Vdmabuf driver
>
> On Fri, Feb 12, 2021 at 08:15:12AM +0000, Kasireddy, Vivek wrote:
> > Hi Gerd,
> >
> > > > > You don't have to use the rendering pipeline. You can let the
> > > > > i915 gpu render into a dma-buf shared with virtio-gpu, then use
> > > > > virtio-gpu only for buffer sharing with the host.
> > [Kasireddy, Vivek] Just to confirm my understanding of what you are
> > suggesting, are you saying that we need to either have Weston allocate
> > scanout buffers (GBM surface/BO) using virtio-gpu and render into them
> > using i915; or have virtio-gpu allocate pages and export a dma-buf and
> > have Weston create a GBM BO by calling gbm_bo_import(fd) and render into
> the BO using i915?
>
> Not sure what the difference between the former and the latter is.
>
> > > Hmm, why a big mode switch? You should be able to do that without
> > > modifying the virtio-gpu guest driver. On the host side qemu needs
> > > some work to support the most recent virtio-gpu features like the
> > > buffer uuids (assuming you use qemu userspace), right now those are only
> supported by crosvm.
> > [Kasireddy, Vivek] We are only interested in Qemu UI at the moment but
> > if we were to use virtio-gpu, we are going to need to add one more vq
> > and support for managing buffers, events, etc.
>
> Should be easy and it should not need any virtio-gpu driver changes.
>
> You can use virtio-gpu like a dumb scanout device. Create a dumb bo, create a
> framebuffer for the bo, map the framebuffer to the crtc.
>
> Then export the bo, import into i915, use it as render target. When
> rendering is
> done flush (DRM_IOCTL_MODE_DIRTYFB). Alternatively allocate multiple bo's +
> framebuffers and pageflip.
Hi,
We've got a MR(https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9592)
for this suggested implementation. Comments are welcome. Thanks.
BR,
Tina
>
> Pretty standard workflow for cases where rendering and scanout are handled by
> different devices. As far I know not uncommon in the arm world.
>
> Right now this will involve a memcpy() for any display update because qemu is
> a
> bit behind on supporting recent virtio-gpu features.
>
> take care,
> Gerd
>
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