[U-Boot-Users] [PATCH] 405 OCM warning

Wolfgang Denk wd at denx.de
Fri Jul 2 00:00:09 CEST 2004

In message <20040612190145.GF12815 at pengutronix.de> you wrote:
> any chance to get this in? It took too much time to let anybody else do
the same stuff again...

Ummm... actually I think this is a FAQ which has been answered somewhere
else (http://www.denx.de/twiki/bin/view/PPCEmbedded/Kernel#Section_10.2.
resp. http://lists.linuxppc.org/linuxppc-embedded/200005/msg00157.html
and Documentation/IO-mapping.txt).

> NOTE: for IBM 405GP the On Chip Memory (OCM) is mapped on virtual
> addresses! So take care that you configure it to be mapped
> (CFG_OCM_DATA_ADDR) in an area which is not used by your operating
> system's virtual addresses. For Linux it has to be located above the
> maximum task size (see CONFIG_TASK_SIZE in the Linux configuration).
> Otherwhise you will see strange effects with your user land stack. 

Isn't it the other way round? U-Boot does not use "virtual addresses"
as it doesn't enable the MMU  for  virtual  memory.  It's  the  Linux
kernel  which  uses  a  1:1  physical  to virtual mapping for certain
address ranges. 

Or am I missing something?

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
It is easier to change the specification to fit the program than vice

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