linux-kernel - Re: drm/sun4i: Add missing pixel formats to the vi layer

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Date:   Fri, 20 Sep 2019 13:14:30 +0300
From:   Roman Stratiienko <roman.stratiienko@...ballogic.com>
To:     Maxime Ripard <mripard@...nel.org>
Cc:     Jernej Škrabec <jernej.skrabec@...l.net>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: drm/sun4i: Add missing pixel formats to the vi layer

On Fri, Sep 20, 2019 at 9:20 AM Maxime Ripard <mripard@...nel.org> wrote:
>
> 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@...ballogic.com napisal(a):
> > > From: Roman Stratiienko <roman.stratiienko@...ballogic.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?

Good question. It mentioned in the datasheet
https://linux-sunxi.org/images/7/7b/Allwinner_DE2.0_Spec_V1.0.pdf
on page 95: "All ui layers' alpha is useless"
And my experiments proves it.

My assumption that vi uses post-processing that cuts out alpha values.

>
> Thanks!
> Maxime



-- 
Best regards,
Roman Stratiienko
Global Logic Inc.