linuxppc-dev.lists.ozlabs.org archive mirror
 help / color / mirror / Atom feed
* [PATCH] [POWERPC] [v2] Improved documentation of device tree 'ranges'.
@ 2007-12-04  1:08 Stephen Neuendorffer
  2007-12-04  2:40 ` David Gibson
  0 siblings, 1 reply; 4+ messages in thread
From: Stephen Neuendorffer @ 2007-12-04  1:08 UTC (permalink / raw)
  To: grant.likely, david, linuxppc-dev

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

^ permalink raw reply related	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2007-12-04  5:31 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2007-12-04  1:08 [PATCH] [POWERPC] [v2] Improved documentation of device tree 'ranges' Stephen Neuendorffer
2007-12-04  2:40 ` David Gibson
2007-12-04  3:22   ` Grant Likely
2007-12-04  5:27   ` [PATCH] [POWERPC] [v2] Improved documentation of device tree'ranges' Stephen Neuendorffer

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).