-----Original Message----- From: dri-devel dri-devel-bounces@lists.freedesktop.org On Behalf Of Gerd Hoffmann Sent: Friday, February 12, 2021 7:02 PM To: Kasireddy, Vivek vivek.kasireddy@intel.com Cc: Kim, Dongwon dongwon.kim@intel.com; christian.koenig@amd.com; daniel.vetter@ffwll.ch; dri-devel@lists.freedesktop.org; virtualization@lists.linux-foundation.org; Vetter, Daniel daniel.vetter@intel.com; linux-media@vger.kernel.org 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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