linux-kernel - Re: [PATCH v5 8/8] dt: add documentation of ARM dt boot interface

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Date:	Sat, 30 Apr 2011 00:30:05 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 8/8] dt: add documentation of ARM dt boot interface

On Fri, Apr 29, 2011 at 08:37:24PM -0400, Nicolas Pitre wrote:
> On Fri, 29 Apr 2011, Grant Likely wrote:
> 
> > diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
> > index 50619a0..31d7e8a 100644
> > --- a/Documentation/devicetree/booting-without-of.txt
> > +++ b/Documentation/devicetree/booting-without-of.txt
> [...]
> > +1) Entry point for arch/arm
> > +---------------------------
> > +
> > +   There is one single entry point to the kernel, at the start
> > +   of the kernel image. That entry point supports two calling
> > +   conventions.  A summary of the interface is described here.  A full
> > +   description of the boot requirements is documented in
> > +   Documentation/arm/Booting
> > +
> > +        a) ATAGS interface.  Minimal information is passed from firmware
> > +        to the kernel with a tagged list of predefined parameters.
> > +
> > +                r0 : 0
> > +
> > +                r1 : Machine type number
> > +
> > +                r2 : Physical address of tagged list in system RAM
> > +
> > +        b) Entry with a flattened device-tree block.  Firmware loads the
> > +        physical address of the flattened device tree block (dtb) into r2,
> > +        r1 is not used, but it is considered good practise to use a valid
> > +        machine number as described in Documentation/arm/Booting.
> > +
> > +                r0 : 0
> > +
> > +                r1 : Valid machine type number.  When using a device tree,
> > +                a single machine type number will often be assigned to
> > +                represent a class or family of SoCs.
> > +
> > +                r2 : physical pointer to the device-tree block
> > +                (defined in chapter II) in RAM.  Device tree can be located
> > +                anywhere in system RAM, but it should be aligned on a 64 bit
> > +                boundary.
> > +
> > +   The kernel will differentiate between ATAGS and device tree booting by
> > +   reading the memory pointed to by r1 and looking for either the flattened
> 
> s/r1/r2/

Good catch. Thanks.

g.

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