linux-kernel - Re: [PATCH] drm/sun4i: sun8i: Add support for pixel blend mode property

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Date:   Mon, 6 Jun 2022 11:20:06 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Roman Stratiienko <r.stratiienko@...il.com>
Cc:     Jernej Škrabec <jernej.skrabec@...il.com>,
        wens@...e.org, airlied@...ux.ie, Daniel Vetter <daniel@...ll.ch>,
        Samuel Holland <samuel@...lland.org>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org, megi@....cz,
        Roman Stratiienko <roman.o.stratiienko@...ballogic.com>
Subject: Re: [PATCH] drm/sun4i: sun8i: Add support for pixel blend mode
 property

On Mon, Jun 06, 2022 at 11:17:20AM +0300, Roman Stratiienko wrote:
> Hello Jernej,
> 
> Thank you for having a look.
> 
> вс, 5 июн. 2022 г. в 23:37, Jernej Škrabec <jernej.skrabec@...il.com>:
> >
> > Dne nedelja, 05. junij 2022 ob 17:47:31 CEST je Roman Stratiienko napisal(a):
> > > Allwinner DE2 and DE3 hardware support 3 pixel blend modes:
> > > "None", "Pre-multiplied", "Coverage"
> > >
> > > Add the blend mode property and route it to the appropriate registers.
> > >
> > > Note:
> > > "force_premulti" parameter was added to handle multi-overlay channel
> > > cases in future changes. It must be set to true for cases when more
> > > than 1 overlay layer is used within a channel and at least one of the
> > > overlay layers within a group uses premultiplied blending mode.
> >
> > Please remove this parameter. It's nothing special, so it can be easily added
> > once it's actually needed. For now, it only complicates code.
> 
> I would prefer keeping it if you do not have any strong opinion against it.
> 
> I am working now on exposing all overlays, so it will be needed soon anyway.

KMS assumes pre-multiplied alpha anyway, so we shouldn't need a
parameter to force it: we're always going to force it.

> Also it helps to better understand the COV2PREMULT mode which has not
> the best description in the datasheet. Only after testing this
> register using devmem I became confident on its purpose.

Sounds like a good job for a comment in the source code.

Maxime

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