[U-Boot-Users] mpc8641d and CONFIG_VERY_BIG_RAM (Chris Fester)

[Sebastien Douheret]

Hi Chris,
if you don't defined CONFIG_VERY_BIG_RAM with a big RAM size
like 1GB, you may have another bug when you attempt to boot a
Linux with a ramdisk.
When you have big RAM, you must generally enable HIGHMEM
support in Linux.
If you try to boot an U-Boot image-multi (Kernel + ramdisk)
without setting CONFIG_VERY_BIG_RAM, the ramdisk will be
placed at the end of the memory (upper than 512MB). 
The issue is that ramdisk must not be in HIGHMEM area (Low
Memory 0 to 512MB, High Memory 512MB to 1GB in my example)
because of HIGHMEM is not functional when Kernel attempts to
un-compress ramdisk during init phase.

If you want to keep CONFIG_VERY_BIG_RAM un-define in U-Boot,
you have another tip that force U-Boot to set ramdisk in Low
Memory area. Set "initrd_high" environemental U-Boot parameter
to “no” or to a valid Low memory address (see code of
do_bootm_linux function in cmd_bootm.c file)

Best regards,
Sebastien D.


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