[U-Boot-Users] [PATCH] ppc4xx: Don't use last 256 bytes of SDRAM, workaround for 440EPx CHIP 11 errata

Wolfgang Denk
2008-03-20T10:03:30Z

Hello Stefan,

in message <1206006397-16582-1-git-send-email-sr@denx.de> you wrote:
> Since 440EPx/GRx has problems with accessing the last 256 bytes of SDRAM via
> the Denali DDR/DDR2 controller, we set CONFIG_PRAM to 1 and reserve 1kByte
> of protected RAM. This way this memory will not get "touched" by U-Boot. And
> by passing "mem=${mem}" to the Linux kernel, Linux will not use this area
> either.

Note that this workaround is incomplete.

If you enable shared (between U-Boot and Linux) log buffer, then the
log buffer will go at the end of memory, and the pRAM area will be
allocated below. In this case the problems is not only still present,
but also very likely to hit pretty soon.

> This patch adds this workaround for the following 440EPx boards:
> sequoia, lwmon5. Others should probably follow this example.

OK, the default configs for Sequoia doesn't use shared log buffer, and
the lwmon5 uses CONFIG_ALT_LB_ADDR (i. e. it puts the log buffer in
OCM), so these boards will work.

But any changes to the configuration may easily break this again.

I don't like the idea that each affected board has to fix this
(probably differently) in it's board config file. I would prefer a
fix (common to all affected boards) in one central location.

Best regards,

Wolfgang Denk

--
DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"Unix is simple, but it takes a genius to understand the simplicity."
- Dennis Ritchie