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authorStephen Neuendorffer <stephen.neuendorffer@xilinx.com>2007-12-03 20:08:57 -0500
committerPaul Mackerras <paulus@samba.org>2007-12-05 22:44:30 -0500
commite1fd18656c2963e383d67b7006c0e06c9c1d9c79 (patch)
tree55dc58862eed2da3e9d82f43bd66496b362af3a4
parent773f76b1601d53dc8485675736b845cc3644921a (diff)
[POWERPC] Improved documentation of device tree 'ranges'
This clarifies how 'ranges' properties are used, and 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> Signed-off-by: Paul Mackerras <paulus@samba.org>
-rw-r--r--Documentation/powerpc/booting-without-of.txt13
1 files changed, 9 insertions, 4 deletions
diff --git a/Documentation/powerpc/booting-without-of.txt b/Documentation/powerpc/booting-without-of.txt
index e9a3cb1d6b06..7327f37d78f3 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
711like address space bits, you'll have to add a bus translator to the 711like address space bits, you'll have to add a bus translator to the
712prom_parse.c file of the recent kernels for your bus type. 712prom_parse.c file of the recent kernels for your bus type.
713 713
714The "reg" property only defines addresses and sizes (if #size-cells 714The "reg" property only defines addresses and sizes (if #size-cells is
715is non-0) within a given bus. In order to translate addresses upward 715non-0) within a given bus. In order to translate addresses upward
716(that is into parent bus addresses, and possibly into CPU physical 716(that is into parent bus addresses, and possibly into CPU physical
717addresses), all busses must contain a "ranges" property. If the 717addresses), all busses must contain a "ranges" property. If the
718"ranges" property is missing at a given level, it's assumed that 718"ranges" property is missing at a given level, it's assumed that
719translation isn't possible. The format of the "ranges" property for a 719translation isn't possible, i.e., the registers are not visible on the
720bus is a list of: 720parent bus. The format of the "ranges" property for a bus is a list
721of:
721 722
722 bus address, parent bus address, size 723 bus address, parent bus address, size
723 724
@@ -735,6 +736,10 @@ fit in a single 32-bit word. New 32-bit powerpc boards should use a
7351/1 format, unless the processor supports physical addresses greater 7361/1 format, unless the processor supports physical addresses greater
736than 32-bits, in which case a 2/1 format is recommended. 737than 32-bits, in which case a 2/1 format is recommended.
737 738
739Alternatively, the "ranges" property may be empty, indicating that the
740registers are visible on the parent bus using an identity mapping
741translation. In other words, the parent bus address space is the same
742as the child bus address space.
738 743
7392) Note about "compatible" properties 7442) Note about "compatible" properties
740------------------------------------- 745-------------------------------------