[U-Boot-Users] [PATCH v4] ppc: Add CFG_MEM_TOP_HIDE option to hide memory area that doesn't get "touched"

[Larry Johnson]

Stefan Roese wrote:
> On Thursday 27 March 2008, Larry Johnson wrote:
>> It's clear now, but unfortunately I don't know enough to tell whether it
>> is also correct :-( .  The statement as now written implies that the
>> statement without the clause, i.e., "Only Linux board ports in
>> arch/powerpc with bootwrapper support will have to get fixed in Linux
>> additionally", is also true.  If this is not correct (because boards
>> that do not recalculate their memory size do not need to be fixed in
>> Linux), then you would write: "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 in Linux additionally."
> 
> Now I'm confused. :) 
> 
> Here is the current version I now have in my "master" branch (with your last 
> sentense):
> 
> - CFG_MEM_TOP_HIDE (PPC only):
> 		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 in Linux additionally.
> 
> 		This option can be used as a workaround for the 440EPx/GRx
> 		CHIP 11 errata where the last 256 bytes in SDRAM shouldn't
> 		be touched.
> 
> 		WARNING: Please make sure that this value is a multiple of
> 		the Linux page size (normally 4k). If this is not the case,
> 		then the end address of the Linux memory will be located at a
> 		non page size aligned address and this could cause major
> 		problems.
> 
> Please send a patch to change this description if necessary.
> 
> Thanks.

I'm not explaining it well, you can look at
"http://en.wikipedia.org/wiki/English_relative_clauses" for a better
explanation.  What you have above should be technically correct, at
worse it would be redundant.

Best regards,
Larry