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From: Arnd Bergmann <arnd@arndb.de>
To: HC Yen <hc.yen@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>,
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Subject: Re: [PATCH v4 1/8] ARM: mediatek: Add basic support for mt8127
Date: Tue, 04 Nov 2014 08:39:55 +0100
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On Tuesday 04 November 2014 14:36:45 HC Yen wrote:
> > > +
> > > +#include <dt-bindings/interrupt-controller/irq.h>
> > > +#include <dt-bindings/interrupt-controller/arm-gic.h>
> > > +#include "skeleton64.dtsi"
> > 
> > Cortex a7 is 32 bits, right? So why do you use skeleton64.dtsi?
> 
> Cortex-A7 is 32-bit, but that doesn't mean it can only have 32-bit
> physical address.  With LPAE enabled, we can have physical address more
> than 32 bits.
> 
> The main difference between "skeleton64.dtsi" and "skeleton.dtsi" is
> "#address-cells" property set to 2.  Although there are few sources
> using "skeleton64.dtsi", some of them write "#address-cells = <2>"
> directly in order to have 64-bit address space.  ARM's TC2 reference
> platform (vexpress-v2p-ca15_a7.dts) is an example.
> 
> Some of MediaTek ARMv7 SoCs support address space larger than 4GB. It
> will be convenient to share the sources if we all use 64-bit device
> tree.

Right, in general, I'd use #address-cells=<2> for Cortex-A7/A15/A17.

	Arnd