Oh, the many joys of MTD...

Kevin Jacobs jacobs at penguin.theopalgroup.com
Thu Mar 8 12:40:13 EST 2001

On Thu, 8 Mar 2001, Vipin Malik wrote:
> > The device mapping is done with the ioremap() call which is responsible for
> > providing a non-cacheable mapping.
> Actually I had to use ioremap_nocache() call with my ELANSC520 processor
> (which has a processor I&D cache). This is even with caching actually
> disabled for the flash banks inside the processor (by the startup
> processor init code).

This is exactly the configuration I have -- its a Lineo SecureEdge (NETtel)
2580 which is based on an AMD Elan SC520 chip.

> Does ioremap() do any caching of it's own? What's the diff between the two?

The difference is:

extern inline void * ioremap (unsigned long offset, unsigned long size)
        return __ioremap(offset, size, 0);


extern inline void * ioremap_nocache (unsigned long offset, unsigned long size)
        return __ioremap(offset, size, _PAGE_PCD);

This in turn adds _PAGE_PCD to the set_pte() call in __ioremap.  This turns
off the page cache for the mapped area.  I'm still not sure why this matters
though I think its inspired me to re-read the literature on the fiddly bits
of i386 architecture.


Kevin Jacobs
The OPAL Group - Enterprise Systems Architect
Voice: (216) 986-0710 x 19         E-mail: jacobs at theopalgroup.com
Fax:   (216) 986-0714              WWW:    http://www.theopalgroup.com

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