MTD and XIP
Dan Post
postster at gmail.com
Sat Nov 6 01:59:20 EST 2004
On Fri, 5 Nov 2004 21:08:35 -0500 (EST), Nicolas Pitre <nico at cam.org> wrote:
> Just to let you all know that I committed to CVS my work on making MTD
> deal with flash used for XIP purpose. At the moment it only supports
> Intel compatible flash on a SA11x0 or PXA2xx based system, but it should
> be easy to extend to other configurations as well.
Nicolas,
This is very cool. I scanned through the code briefly, and will take
a look at it first chance I get next week (OK, it might be a little
later; I am pretty swamped). I had hoped to get to doing this sort of
thing in the next few months (i.e. doing XIP support *right* and on a
*relevant* kernel), so I was glad to see your work. It looks very
clean, but I haven't run a fine-tooth comb through it.
However, the automated post to the CVS list reported:
***** Error reading new file: [Errno 2] No such file or directory: 'xip.h'
Do you have a specific reason to always disable write suspend on XIP
kernels? That's a pretty big latency hit, and I don't think we need
to disable it for XIP systems.
I saw your comment that "the XIP system config appears to have
problems using write suspend at the moment". Any specifics?
I suppose one of these days I'll have to get around to doing empirical
measurements on the effect write suspend on busy systems has to write
throughput. I seem to remember someone else, perhaps David, did that
a while back.
What kind of changes does this require to the map file? This does
interrupt-pollihg (software-read-while-write, SW/RWW) all the time.
(Right?) I think we can add intelligence to the map file, and set a
bit for each hardware partition that has XIP code in it (e.g. kernel,
linear^XIP CRAMFS, ...), so, for instance, we don't constantly suspend
writes / erases to partitions that don't ever have XIP code in them
just because an interrupt happens in the system. A la my old kludgy
version for 2.4.
More thoughts to come later...
> Also for those interested in making their kernel XIP on ARM, you can
> look at the following patches against Linux-2.6.9:
> http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=2154/1
> http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=2160/1
Once again, cool. I suppose I should follow the ARM-Linux patch
repository a little closer, too... :)
Cheers,
Dan Post
(Yes, this is my new mail account. Handy for mailing lists.)
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