[Spice-devel] [virtio-dev] Re: [PATCH v2 0/1] VirtIO video device specification

[Gerd Hoffmann]

On Mon, Jan 13, 2020 at 11:41:45AM +0100, Dmitry Sepp wrote:
> Hi Gerd,
> 
> Thanks for reviewing!
> 
> On Montag, 13. Januar 2020 10:56:36 CET Gerd Hoffmann wrote:
> >   Hi,
> > 
> > > This also means that we cannot have unspec for planes layout. Device
> > > either
> > > expects planes in separate buffers or in one buffer with some offsets,
> > > there cannot be mixed cases.
> > 
> > Hmm.  Is it useful to support both?  Or maybe support the "one buffer +
> > offsets" case only?  Splitting one buffer into multiple smaller ones
> > internally if needed shouldn't be a problem, and it would simplify the
> > interface a bit ...
> > 
> 
> Ok, let's consider the following case:
>  - the device expects planes in separate buffers.
>  - say, Android on the guest side also imports planes in separate buffers into the driver.
>  - but he driver only supports one buffer + offsets.
> 
> Do you mean the driver then can join the underlying page lists and set offsets then? Yes, 
> this would probably make sense.

Well, no.  Tomasz Figa had splitted the devices into three groups:

  (1) requires single buffer.
  (2) allows any layout (including the one (1) devices want).
  (3) requires per-plane buffers.

Category (3) devices are apparently rare and old.  Both category (1)+(2)
devices can handle single buffers just fine.  So maybe support only
that?

Hope it's more clear this time,
  Gerd