[U-Boot] Kernel patch for CONFIG_LOGBUFFER

[Detlev Zundel]

Hi Serguei,

> I'm looking for a working patch for the Linux kernel 2.6.28.8 that
> would allow using CONFIG_LOGBUFFER (a kernel log buffer shared between
> U-Boot and the kernel). I'm using u-boot 1.3.3. When LOGBUFFER is
> enabled in the kernel configuration the kernel build fails with:
> kernel/built-in.o: In function `setup_ext_logbuff': : undefined
> reference to `setup_ext_logbuff_mem'

This is to be expected - CONFIG_LOGBUFFER only worked with arch/ppc.  It
is broken since the arch/ppc removal and nobody (yet) cared to get it to
life again.  Only recently there were discussions on the linux-embedded
ml[1] which may yield other solutions going mainline.

> Could anybody also tell me how the buffer location (I think the size
> is fixed to 16K) is communicated to the kernel, via a kernel command
> line parameter? If so, what is it?

It was placed at a known address relative to the end of RAM.  Check
arch/ppc/mm/init.c e.g. in our DENX-v2.6.25-stable branch.

Cheers
  Detlev

[1] http://www.mail-archive.com/linux-embedded@vger.kernel.org/msg01945.html

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