[PATCH] [POWERPC] [v2] Improved documentation of device tree 'ranges'.

[PATCH] [POWERPC] [v2] Improved documentation of device tree 'ranges'.

[Stephen Neuendorffer]

I was misled by the prior language.  I've attempted to clarify how
'ranges' are used, in particular, how to get an identity mapping.

Signed-off-by: Stephen Neuendorffer <stephen.neuendorffer@xilinx.com>
---
 Documentation/powerpc/booting-without-of.txt |   13 +++++++++----
 1 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/Documentation/powerpc/booting-without-of.txt b/Documentation/powerpc/booting-without-of.txt
index e9a3cb1..7327f37 100644
--- a/Documentation/powerpc/booting-without-of.txt
+++ b/Documentation/powerpc/booting-without-of.txt
@@ -711,13 +711,14 @@ define a bus type with a more complex address format, including things
 like address space bits, you'll have to add a bus translator to the
 prom_parse.c file of the recent kernels for your bus type.
 
-The "reg" property only defines addresses and sizes (if #size-cells
-is non-0) within a given bus. In order to translate addresses upward
+The "reg" property only defines addresses and sizes (if #size-cells is
+non-0) within a given bus. In order to translate addresses upward
 (that is into parent bus addresses, and possibly into CPU physical
 addresses), all busses must contain a "ranges" property. If the
 "ranges" property is missing at a given level, it's assumed that
-translation isn't possible. The format of the "ranges" property for a
-bus is a list of:
+translation isn't possible, i.e., the registers are not visible on the
+parent bus.  The format of the "ranges" property for a bus is a list
+of:
 
 	bus address, parent bus address, size
 
@@ -735,6 +736,10 @@ fit in a single 32-bit word.   New 32-bit powerpc boards should use a
 1/1 format, unless the processor supports physical addresses greater
 than 32-bits, in which case a 2/1 format is recommended.
 
+Alternatively, the "ranges" property may be empty, indicating that the
+registers are visible on the parent bus using an identity mapping
+translation.  In other words, the parent bus address space is the same
+as the child bus address space.
 
 2) Note about "compatible" properties
 -------------------------------------
-- 
1.5.3.4-dirty

Re: [PATCH] [POWERPC] [v2] Improved documentation of device tree 'ranges'.

[David Gibson]

On Mon, Dec 03, 2007 at 05:08:57PM -0800, Stephen Neuendorffer wrote:
> I was misled by the prior language.  I've attempted to clarify how
> 'ranges' are used, in particular, how to get an identity mapping.
> 
> Signed-off-by: Stephen Neuendorffer <stephen.neuendorffer@xilinx.com>

Acked-by: David Gibson <david@gibson.dropbear.id.au>

Thanks for the update.  I particularly dislike the "1:1" terminology,
because in maths-speak *any* ranges translation is 1:1, unless it
includes overlapping ranges.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

Re: [PATCH] [POWERPC] [v2] Improved documentation of device tree 'ranges'.

[Grant Likely]

On 12/3/07, David Gibson <david@gibson.dropbear.id.au> wrote:
>
> On Mon, Dec 03, 2007 at 05:08:57PM -0800, Stephen Neuendorffer wrote:
> > I was misled by the prior language.  I've attempted to clarify how
> > 'ranges' are used, in particular, how to get an identity mapping.
> >
> > Signed-off-by: Stephen Neuendorffer <stephen.neuendorffer@xilinx.com>
>
> Acked-by: David Gibson <david@gibson.dropbear.id.au>

Acked-by: Grant Likely <grant.likely@secretlab.ca>

>
> Thanks for the update.  I particularly dislike the "1:1" terminology,
> because in maths-speak *any* ranges translation is 1:1, unless it
> includes overlapping ranges.
>
> --
> David Gibson                    | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
>                                 | _way_ _around_!
> http://www.ozlabs.org/~dgibson
>


-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
grant.likely@secretlab.ca
(403) 399-0195

RE: [PATCH] [POWERPC] [v2] Improved documentation of device tree'ranges'.

[Stephen Neuendorffer]

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I'm actually a little embarrassed that I didn't pick that nit myself.. :)

-----Original Message-----
From: David Gibson [mailto:david@gibson.dropbear.id.au]
Sent: Mon 12/3/2007 6:40 PM
To: Stephen Neuendorffer
Cc: grant.likely@secretlab.ca; linuxppc-dev@ozlabs.org
Subject: Re: [PATCH] [POWERPC] [v2] Improved documentation of device tree'ranges'.
 

On Mon, Dec 03, 2007 at 05:08:57PM -0800, Stephen Neuendorffer wrote:
> I was misled by the prior language.  I've attempted to clarify how
> 'ranges' are used, in particular, how to get an identity mapping.
> 
> Signed-off-by: Stephen Neuendorffer <stephen.neuendorffer@xilinx.com>

Acked-by: David Gibson <david@gibson.dropbear.id.au>

Thanks for the update.  I particularly dislike the "1:1" terminology,
because in maths-speak *any* ranges translation is 1:1, unless it
includes overlapping ranges.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson



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