linux-kernel - Re: [PATCH v7 01/18] soc: mediatek: Disable 9-bit alpha in ETHDR

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Date: Tue, 7 May 2024 10:02:14 +0000
From: Shawn Sung (宋孝謙) <Shawn.Sung@...iatek.com>
To: CK Hu (胡俊光) <ck.hu@...iatek.com>,
	"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
	"angelogioacchino.delregno@...labora.com"
	<angelogioacchino.delregno@...labora.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	Bibby Hsieh (謝濟遠) <Bibby.Hsieh@...iatek.com>,
	"jason-ch.chen@...iatek.corp-partner.google.com"
	<jason-ch.chen@...iatek.corp-partner.google.com>,
	Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
	"daniel@...ll.ch" <daniel@...ll.ch>, "p.zabel@...gutronix.de"
	<p.zabel@...gutronix.de>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>, "airlied@...il.com" <airlied@...il.com>,
	"sean@...rly.run" <sean@...rly.run>, "matthias.bgg@...il.com"
	<matthias.bgg@...il.com>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v7 01/18] soc: mediatek: Disable 9-bit alpha in ETHDR

Hi CK,

On Tue, 2024-05-07 at 05:58 +0000, CK Hu (胡俊光) wrote:
> Hi, Shawn:
> 
> On Thu, 2024-05-02 at 18:38 +0800, Shawn Sung wrote:
> > From: Hsiao Chien Sung <shawn.sung@...iatek.com>
> > 
> > ETHDR 9-bit alpha should be disabled by default,
> > otherwise alpha blending will not work.
> 
> Please explain what is 9-bit alpha. Is ARGB8888 8-bit alpha? I don't
> know there are 9-bit alpha. I would like to know which function would
> be disabled when you disable 9-bit alpha.
> 

When 9-bit alpha is enabled, the original alpha range 0-255 will be
remapped to 0-256 (255 = N/A) for some special case calculation.
Checked with the designer, this setting should be always disabled and
there will be no side effects.

Thanks,
Shawn