* Re: RFC: Put printk buffer in video ram
[not found] ` <4B0ADA84.5050300@nortel.com>
@ 2009-11-23 19:03 ` Arnd Bergmann
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From: Arnd Bergmann @ 2009-11-23 19:03 UTC (permalink / raw)
To: Chris Friesen
Cc: Maxim Levitsky, Frederic Weisbecker, linuxppc-dev, linux-kernel,
Steven Rostedt, Dave Jones, Ingo Molnar, Linus Torvalds,
Andrew Morton, Arjan van de Ven
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 <><
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