diff options
| author | Stephen Neuendorffer <stephen.neuendorffer@xilinx.com> | 2007-12-04 12:08:57 +1100 |
|---|---|---|
| committer | Paul Mackerras <paulus@samba.org> | 2007-12-06 14:44:30 +1100 |
| commit | e1fd18656c2963e383d67b7006c0e06c9c1d9c79 (patch) | |
| tree | 55dc58862eed2da3e9d82f43bd66496b362af3a4 /Documentation/powerpc | |
| parent | 773f76b1601d53dc8485675736b845cc3644921a (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>
Diffstat (limited to 'Documentation/powerpc')
| -rw-r--r-- | 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 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 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 ------------------------------------- |