From: Stephen Neuendorffer <stephen.neuendorffer@xilinx•com>
To: grant.likely@secretlab•ca, david@gibson•dropbear.id.au,
linuxppc-dev@ozlabs•org
Subject: [PATCH] [POWERPC] Improved documentation of device tree 'ranges'.
Date: Mon, 3 Dec 2007 09:45:03 -0800 [thread overview]
Message-ID: <20071203174403.C740719B0073@mail119-sin.bigfish.com> (raw)
I was misled by the prior language. I've attempted to clarify how
'ranges' are used, in particular, how to get a 1:1 mapping.
Signed-off-by: Stephen Neuendorffer <stephen.neuendorffer@xilinx•com>
---
Documentation/powerpc/booting-without-of.txt | 11 +++++++----
1 files changed, 7 insertions(+), 4 deletions(-)
diff --git a/Documentation/powerpc/booting-without-of.txt b/Documentation/powerpc/booting-without-of.txt
index e9a3cb1..aad8bf5 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 +736,8 @@ 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, with 1:1 address translation.
2) Note about "compatible" properties
-------------------------------------
--
1.5.3.4
next reply other threads:[~2007-12-03 17:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-03 17:45 Stephen Neuendorffer [this message]
2007-12-03 18:09 ` [PATCH] [POWERPC] Improved documentation of device tree 'ranges' Grant Likely
2007-12-04 0:52 ` David Gibson
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