linux-kernel - Re: [PATCH 1/2] dt-bindings: add binding for A64 DE2 CCU with SRAM section

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Message-ID: <b8c770bdc7a0541b8d1179598d814b75@aosc.io>
Date:   Fri, 27 Oct 2017 22:33:29 +0800
From:   icenowy@...c.io
To:     Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     devicetree@...r.kernel.org, linux-sunxi@...glegroups.com,
        linux-kernel@...r.kernel.org, Chen-Yu Tsai <wens@...e.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] dt-bindings: add binding for A64 DE2 CCU with SRAM
 section

在 2017-10-16 20:09，Maxime Ripard 写道：
> On Mon, Oct 16, 2017 at 05:41:10PM +0800, icenowy@...c.io wrote:
>> 在 2017-10-16 17:11，Maxime Ripard 写道：
>> > On Sat, Oct 14, 2017 at 08:29:24PM +0800, Icenowy Zheng wrote:
>> > > A64's Display Engine 2.0 needs a section of SRAM (SRAM C) to be
>> > > claimed.
>> >
>> > Why?
>> 
>> Allwinner didn't document this, but if the SRAM is not claimed, the
>> DE2 MMIO zone is totally not accessible.
> 
> Not accessible how? It generates an abort when you access it? It
> returns 0?
> 
>> It seems that Allwinner uses the SRAM C in the DE2 internally.
> 
> Then shouldn't it be tied to all the DE2 devices then? So mixers
> too. Either way, this should be mentionned in your commit logs. How
> you're fixing things is much less interesting than why you're doing
> them. You can tell how you're doing them from your code already.

Yes I checked and when the SRAM is not claimed any part in DE2 memory
zone can't be accessed.

Should I also add the code that claims the SRAM in the mixer code? Or
just place the device tree property is enough? (As the mixers depend
on the DE2 CCU) Or just ignore this?

> 
> Maxime
> 
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