[PATCH v16 5/6] vfio: ABI for mdev display dma-buf operation

[Zhang, Tina]

> -----Original Message-----
> From: intel-gvt-dev [mailto:intel-gvt-dev-bounces at lists.freedesktop.org] On
> Behalf Of Gerd Hoffmann
> Sent: Tuesday, November 7, 2017 4:03 PM
> To: Zhang, Tina <tina.zhang at intel.com>; alex.williamson at redhat.com;
> chris at chris-wilson.co.uk; joonas.lahtinen at linux.intel.com;
> zhenyuw at linux.intel.com; Lv, Zhiyuan <zhiyuan.lv at intel.com>; Wang, Zhi A
> <zhi.a.wang at intel.com>; Tian, Kevin <kevin.tian at intel.com>; daniel at ffwll.ch;
> kwankhede at nvidia.com
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>; intel-gfx at lists.freedesktop.org;
> intel-gvt-dev at lists.freedesktop.org; linux-kernel at vger.kernel.org
> Subject: Re: [PATCH v16 5/6] vfio: ABI for mdev display dma-buf operation
> 
>   Hi,
> 
> > > Add a head field here?  People asked @ kvm forum about multihead
> > > support.
> > > Even if the initial driver version doesn't support it we could add a
> > > field so it becomes easier to add it at some point in the future.
> > >
> > > Probing for available heads could be done with the PROBE flag, i.e.
> > > flags = PROBE | DMABUF, plane_type = PRIMARY, head = 0, 1, ...
> >
> > Does the multihead mean multiple display monitor? So each head can
> > have its own one primary plane, one cursor plane and maybe some sprite
> > planes if supported.
> 
> Yes and yes.
> 
> > And the flow could be like this:
> > 1) flags = PROBE | DMABUF, then return the number of heads in
> > vfio_device_gfx_plane_info.head.
> 
> I'd suggest to use { .flags = PROBE | DMABUF, .head = 0 } to check whenever
> dmabuf is supported for head 0, then { .flags = PROBE | DMABUF, .head = 1 } to
> check for head 1 support, ...
> 
> Driver returns success if the head is supported and -EINVAL otherwise, simliar to
> the dmabuf vs. region probing.
> 
> It is less confusing because .head is always an input field then.
> 
> It is also a bit more flexible because different heads can support different modes
> (I don't expect drivers will actually use that though).
> 
> > 2) flags = DMABUF with plane_type = PRIMARY, head = 0, 1, ..., then
> > return the id of the exposed framebuffer of that head.
> 
> Yes.
> 
> > Another question is if the sprite plane is supported, how we're going
> > to identify them, as there could be several sprite planes for one
> > display monitor.
> 
> Do you mean DRM_PLANE_TYPE_OVERLAY?
Yes.

> 
> > Add another field "num_plane" for it? Then, I guess the flow could be
> > like this:
> > 1) flags = PROBE | DMABUF, then return the number of heads in
> > vfio_device_gfx_plane_info.head.
> > 2) flags = PROBE | DMABUF and head = 0, 1, ..., and plane_type =
> > PRIMARY/CURSOR/SPRITE, then return the num_plane.
> 
> I'd suggest to do it simliar to the head probe outlined above, i.e.
> userspace calls { .flags = PROBE | DMABUF, .head = 0, .plane_type = OVERLAY,
> plane_num = 0, 1, 2, ... } and the driver returns -EINVAL or 0 depending on
> whenever it is supported or not.
Agree. Thanks.

BR,
Tina
> 
> cheers,
>   Gerd
> 
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