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

Gerd Hoffmann
2020-01-13T11:05:33Z

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