On Mon, Dec 03, 2007 at 09:45:03AM -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 a 1:1 mapping.
Sounds good, except for one detail. I think we should avoid using
the "1:1" terminology: to a mathematician, at least, "1:1" is much
weaker than "identity mapping" which is what an empty ranges actually
implies.
So, I think we should explicitly say that an empty ranges implies that
parent bus address space is identical to child bus address space.
> Signed-off-by: Stephen Neuendorffer <[EMAIL PROTECTED]>
> ---
> 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
> -------------------------------------
--
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
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@ozlabs.org
https://ozlabs.org/mailman/listinfo/linuxppc-dev
