Re: [PATCH v3] drm/virtio: add new virtio gpu capset definitions

[Akihiko Odaki]

On 2023/10/19 8:25, Gurchetan Singh wrote:
> On Tue, Oct 10, 2023 at 9:41 PM Huang Rui <ray.huang@xxxxxxx 
> <mailto:ray.huang@xxxxxxx>> wrote:
>
>     On Tue, Oct 10, 2023 at 11:52:14PM +0800, Dmitry Osipenko wrote:
>      > On 10/10/23 18:40, Dmitry Osipenko wrote:
>      > > On 10/10/23 16:57, Huang Rui wrote:
>      > >> These definitions are used fro qemu, and qemu imports this
>     marco in the
>      > >> headers to enable gfxstream, venus, cross domain, and drm (native
>      > >> context) for virtio gpu. So it should add them even kernel
>     doesn't use
>      > >> this.
>      > >>
>      > >> Signed-off-by: Huang Rui <ray.huang@xxxxxxx
>     <mailto:ray.huang@xxxxxxx>>
>      > >> Reviewed-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx
>     <mailto:akihiko.odaki@xxxxxxxxxx>>
>      > >> ---
>      > >>
>      > >> Changes V1 -> V2:
>      > >> - Add all capsets including gfxstream and venus in kernel
>     header (Dmitry Osipenko)
>      > >>
>      > >> Changes V2 -> V3:
>      > >> - Add missed capsets including cross domain and drm (native
>     context)
>      > >>   (Dmitry Osipenko)
>      > >>
>      > >> v1:
>     https://lore.kernel.org/lkml/20230915105918.3763061-1-ray.huang@xxxxxxx/ <https://lore.kernel.org/lkml/20230915105918.3763061-1-ray.huang@xxxxxxx/>
>      > >> v2:
>     https://lore.kernel.org/lkml/20231010032553.1138036-1-ray.huang@xxxxxxx/ <https://lore.kernel.org/lkml/20231010032553.1138036-1-ray.huang@xxxxxxx/>
>      > >>
>      > >>  include/uapi/linux/virtio_gpu.h | 4 ++++
>      > >>  1 file changed, 4 insertions(+)
>      > >>
>      > >> diff --git a/include/uapi/linux/virtio_gpu.h
>     b/include/uapi/linux/virtio_gpu.h
>      > >> index f556fde07b76..240911c8da31 100644
>      > >> --- a/include/uapi/linux/virtio_gpu.h
>      > >> +++ b/include/uapi/linux/virtio_gpu.h
>      > >> @@ -309,6 +309,10 @@ struct virtio_gpu_cmd_submit {
>      > >>
>      > >>  #define VIRTIO_GPU_CAPSET_VIRGL 1
>      > >>  #define VIRTIO_GPU_CAPSET_VIRGL2 2
>      > >> +#define VIRTIO_GPU_CAPSET_GFXSTREAM 3
>      > >
>      > > The GFXSTREAM capset isn't correct, it should be
>     GFXSTREAM_VULKAN in
>      > > accordance to [1] and [2]. There are more capsets for GFXSTREAM.
>      > >
>      > > [1]
>      > >
>     https://github.com/google/crosvm/blob/main/rutabaga_gfx/src/rutabaga_utils.rs#L172 <https://github.com/google/crosvm/blob/main/rutabaga_gfx/src/rutabaga_utils.rs#L172>
>      > >
>      > > [2]
>      > >
>     https://patchwork.kernel.org/project/qemu-devel/patch/20231006010835.444-7-gurchetansingh@xxxxxxxxxxxx/ <https://patchwork.kernel.org/project/qemu-devel/patch/20231006010835.444-7-gurchetansingh@xxxxxxxxxxxx/>
>      >
>      > Though, maybe those are "rutabaga" capsets that not related to
>      > virtio-gpu because crosvm has another defs for virtio-gpu capsets
>     [3].
>      > The DRM capset is oddly missing in [3] and code uses "rutabaga"
>     capset
>      > for DRM and virtio-gpu.
>      >
>      > [3]
>      >
>     https://github.com/google/crosvm/blob/main/devices/src/virtio/gpu/protocol.rs#L416 <https://github.com/google/crosvm/blob/main/devices/src/virtio/gpu/protocol.rs#L416>
>
>     Yes, [3] is the file that I referred to add these capsets
>     definitions. And
>     it's defined as gfxstream not gfxstream_vulkan.
>
>      >
>      > Gurchetan, could you please clarify which capsets definitions are
>      > related to virtio-gpu and gfxstream. The
>      > GFXSTREAM_VULKAN/GLES/MAGMA/COMPOSER or just the single GFXSTREAM?
>
>
> It should be GFXSTREAM_VULKAN.  The rest are more experimental and easy 
> to modify in terms of the enum value, should the need arise.
>
> I imagine the virtio-spec update to reflect the GFXSTREAM to 
> GFXSTREAM_VULKAN change will happen eventually.

I think this is a matter what the committee should determine, but in 
general I don't think it is OK to change the existing identifier.

I also think even experimental values should be added to virtio spec at 
an early stage unless such an "experiment" is done only on one laptop. 
We can obsolete a capset anytime so it's more important to avoid 
conflicts of capsets.