[U-Boot] [coreboot] U-Boot-x86 / coreboot Integration

[Wolfgang Denk]

Dear Peter Stuge,

In message <20110510160850.2499.qmail at stuge.se> you wrote:
>
> >  - U-Boot relocates to 'Top of RAM' - This is a fundamental architectural
> >    design and not x86 specific. This feature should be retained for
> >    consistency with other U-Boot arches
> 
> IMO this might be a little misguided. Retaining behavior, especially
> across architecture, shouldn't be an end in itself. If U-Boot was the
> primary bootloader in this situation it would matter less. In the
> context of coreboot however U-Boot would be much easier to integrate
> with if this policy was not enforced. Maybe U-Boot wants to stay
> resident however, then there's not much choice except top of memory.

It's not about staying resident, but for a number of other features
that are considered valuable, like:
- auto-adapting to the available RAM size so a maximum amount of
  contiguous RAM is available to load OS and/or file system images,
  etc.
- providing "persistent RAM" which keeps it's content even through a
  reset/crash/warmboot; frequently used for in-memory file systems
  (pramfs for example)
- sharing a log buffewr between U-Boot and Linux, so Linux can pick up
  U-Boot's POST codes using standard syslog tools, or U-Boot can read
  the Linux log buffer after a system crash - or Linux can pick up the
  last entries of the previous Linux kernel's messages after a
  crash/reboot
- sharing video RAM, so we can load a splash screen in U-Boot which
  can be assedon without any flicker to Linux, until application code
  starts drawing it's own graphics.
etc.

All these are based on the idea to reserve memory chunks from the top
of physical RAM.  And U-Boot is sitting just below all these reserved
chunks.

Best regards,

Wolfgang Denk

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