drm/sun4i: Add missing pixel formats to the vi layer

[Maxime Ripard]

On Thu, Sep 19, 2019 at 08:53:10PM +0200, Jernej Škrabec wrote:
> Dne sreda, 18. september 2019 ob 13:05:41 CEST je
> roman.stratiienko at globallogic.com napisal(a):
> > From: Roman Stratiienko <roman.stratiienko at globallogic.com>
> >
> > According to Allwinner DE2.0 Specification REV 1.0, vi layer supports the
> > following pixel formats:  ABGR_8888, ARGB_8888, BGRA_8888, RGBA_8888
>
> It's true that DE2 VI layers support those formats, but it wouldn't change
> anything because alpha blending is not supported by those planes. These
> formats were deliberately left out because their counterparts without alpha
> exist, for example ABGR8888 <-> XBGR8888. It would also confuse user, which
> would expect that alpha blending works if format with alpha channel is
> selected.

I'm not too familiar with the DE2 code, but why is alpha not working
if the VI planes support formats with alpha?

Thanks!
Maxime
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