RFC: Put printk buffer in video ram

[Arnd Bergmann]

On Monday 23 November 2009, Chris Friesen wrote:
> We've had a mechanism sort of like this for quite a while.  Hasn't been
> pushed to mainline because it used board-specific hardware and we're
> usually multiple kernel versions behind mainline.
> 
> Anyways, a couple things that we've found to be useful are:
> 1) The ability to allocate a chunk of this persistent memory area for a
> special purpose.  This allows things like memory-mapped circular buffers
> for per-cpu binary data.
> 2) An API to log just to this persistent area and bypass the normal
> console completely.  This can be useful when debugging issues where the
> normal logging paths result in a hang.

Some powerpc machines have a memory-mapped nvram, in which the kernel
can install persistant 'partitions'. Not all of them are memory mapped,
but for those that are (e.g. IBM QS22), your approach sounds perfect.

	Arnd <><