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

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Date:   Fri, 27 Oct 2017 17:13:34 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     icenowy@...c.io
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

On Fri, Oct 27, 2017 at 10:33:29PM +0800, icenowy@...c.io wrote:
> 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.

Then all the nodes that depend on it should have it, and the bindings
should be modified appropriately.

Maxime

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

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