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

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Message-ID: <20171016120912.lxu7rikhffxsu5o4@flea.lan>
Date:   Mon, 16 Oct 2017 14:09:12 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     icenowy@...c.io
Cc:     devicetree@...r.kernel.org, Chen-Yu Tsai <wens@...e.org>,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com,
        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

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.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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