[U-Boot-Users] [PATCH v3] ppc: Add CFG_MEM_TOP_HIDE option to hide memory area that doesn't get "touched"

[Stefan Roese]

On Wednesday 26 March 2008, Wolfgang Denk wrote:
> In message <1206518897-15473-1-git-send-email-sr at denx.de> you wrote:
> > If CFG_MEM_TOP_HIDE is defined in the board config header, this specified
> > memory area will get subtracted from the top (end) of ram and won't get
> > "touched" at all by U-Boot. By fixing up gd->ram_size the Linux kernel
> > should gets passed the now "corrected" memory size and won't touch it
> > either. This should work for arch/ppc and arch/powerpc. Only Linux board
> > ports in arch/powerpc with bootwrapper support, that recalculate the
> > memory size from the SDRAM controller setup will have to get fixed.
>
> I'm afraid we still have a problem here...
>
> > - Changed value of CFG_MEM_TOP_HIDE from 256 to 4k so that memory
> >   end location is on a page boundary
>
> This assumes a page size of 4 KiB, which is not necessarily true.  As
> you  know,  we  also  support page sizes of 16, 64 and 256 KiB on 44x
> systems (even though so far this is only avaiable in arch/ppc).

Right. Unfortunately I can't take care of this in an other way as to set this 
define to the max possible page size value. And I don't think this is 
acceptable, since removing 256k (or even more) from all Sequoia's and other 
440EPx boards isn't a good idea.

> I don't know of a good way to fix this, but I ask that you  at  least
> document  the  new  variable in the README and probably add a big fat
> warning for page sizes other than 4 KiB.

OK, will do.

Best regards,
Stefan

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