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

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Date:   Mon, 6 Jun 2022 11:22:25 +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 11:20:06AM +0200, Maxime Ripard wrote:
> 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.

My bad, I got confused with your other patch.

Still, I agree with Jernej, if it's not needed it only complicates the
code for no particular reason. If you need it at some point in the
future, add it then. Otherwise, it's hard to reason about, since we
don't know what are the expectations that those future patches will
bring.

Maxime

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