[PATCH weston] simple-dmabuf-drm: use GBM generic calls

[Daniel Stone]

Hi,
On Wed, 11 Jul 2018 at 09:16, Pekka Paalanen <ppaalanen at gmail.com> wrote:
> On Tue, 10 Jul 2018 17:53:15 +0200 Emilio Pozuelo Monfort <pochu27 at gmail.com> wrote:
> > No need to write libdrm driver specific code for each supported
> > driver, we can just let GBM call the right one for us now.
> >
> > Signed-off-by: Emilio Pozuelo Monfort <emilio.pozuelo at collabora.co.uk>
> > ---
> >
> > Hi,
> >
> > This simplifies the code a lot, using gbm_bo as Emil suggested. Some problems
> > I still see:
> >
> > - NV12 doesn't work, it seems that backends/dri/gbm_dri.c:gbm_format_to_dri_format()
> >   doesn't support it.
>
> I think NV12 and other less common formats, should someone add them in
> this program, should not be lost. That may be part of the reason GBM
> wasn't used: the need to test YUV formats, and non-GPU-renderable
> formats in general.

Honestly, most of the reason was because I wrote the original client
in about 15 minutes on a very short bus trip. You can probably see
that in comments like 'XXX: would be nice to draw something that
changes here'. So I don't think you can really read too much into the
original code.

Other great reasons include:
  - we wanted to explicitly get modifiers allocated, and this was
before the GBM modifiers interface existed
  - at the time, I was doing bring-up of a GBM implementation which
wasn't usable by generic clients (privileged allocation only)
  - YUV format support

I'm pretty ambivalent about it though. V4L2 and Vivid might well cover
the YUV case well enough, and even if not, GBM should still be able to
allocate R/RG buffers.

Cheers,
Daniel