IMAP_ADDR on PPC 8xx

[Wolfgang Denk]

In message <1147108983.27101.63.camel at excalibur.timesys.com> you wrote:
> 
> In particular, I have an MPC885ADS board running "U-Boot 1.1.3 (Apr 19
> 2005 - 13:39:58)".  It will boot neither 2.6.15 nor 2.6.16.11.  After
> U-Boot decompresses the kernel, I get no kernel output at all; it just
> hangs.

Probably you forgot to specify a correct  console  device  with  your
boot arguments.

> After some debugging, I think things go awry when the code starts
> dereferencing IMAP_ADDR as a direct pointer.  IMAP_ADDR is defined to be
> 0xFF000000, but the MPC885ADS documentation says that the internal

Correct.

> memory map is supposed to at 0x22000000.  In addition, when I look at
> the bd_t pointer from U-Boot, it's saying that 0x22000000 is the correct
> address.

No. U-Boot uses 0xFF000000. At least the official U-Boot source  tree
does. I don't know where you got yours from, or who might have broken
it.

> Why is this a problem for us and apparently not for anyone else on this
> list?  Is no one else using U-Boot?  Or does everyone else's U-Boot use
> 0xFF000000 instead of 0x22000000?  Or do I have a different problem

Most probably everybody else who uses U-Boot uses a good version with
a high mapping.

> While reading through the archives, I see that using IMAP_ADDR the way
> it is currently used is somewhat frowned upon anyway.  Is this one of
> those things that we (the PPC Linux community) should fix the "right
> way" once and for all?  I'm happy to submit a patch once I understand
> what the "right way" is...  :-)

The memory map requirements of PowerPC systems  have  been  explained
many  times  before,  so a little search in the archives, HOWTOs etc.
should point you quickly for good description why a low mapping  like
0x22000000 cannot work.

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
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