IMAP_ADDR on PPC 8xx

[Walter L. Wimer III]

On Tue, 2006-05-09 at 14:38 -0400, Kenneth Poole wrote:
> In our build, (currently based on 2.6.14.3) we define IMAP_ADDR as
> follows:
> 
> #define IMAP_ADDR       (((bd_t *)__res)->bi_immr_base)

Yes, this is (part of) what our 2.6.11.7-based patch does.


> With very few exceptions, nearly all driver code that dereferences
> IMAP_ADDR can be used unchanged and the IMMR value is always the value
> passed up from the bootloader. We build one image that runs on
> multiple platforms and some platforms place the IMMR address space at
> different addresses than others. It’s not a constant.

Exactly.  I think this kind of "automatic adaption" to the particular
platform is what should be in the vanilla kernel.


> Regardless, I see little reason to ioremap() the IMMR address.

This was the second major part of our 2.6.11.7-based patch.  It
performed a single ioremap(), stored the result in a global pointer, and
then used that pointer in all the drivers instead of using IMAP_ADDR
directly.  Personally, I don't have a strong opinion yet as to whether
this is desirable or not.


> The MMU is set up in such a way that IMMR based locations can be
> accessed directly.

I'm still rather fuzzy on whether one can count on this always being the
case on all PPC variants.  (????)



> Ken Poole, MRV Communications, Inc.


Thanks!

Walt