[PATCH 0/2] arm: add early_ioremap() support

Arnd Bergmann arnd at arndb.de
Wed Jun 26 17:23:50 EDT 2013

On Wednesday 26 June 2013, Leif Lindholm wrote:
> On Wed, Jun 26, 2013 at 08:52:09PM +0200, Arnd Bergmann wrote:
> > I made a similar suggestion to extending the use of fixmap recently, see
> > "Re: SCU registers mapping for CA9/CA5 cores". Russell pointed out that
> > fixmap is intentionally limited to just kmap_atomic uses at the moment
> > and changing that would potentially have a significant impact when we
> > run out of pages in the fixmap area.
> Is this an issue here, since (unlike x86) this early_ioremap only works
> before paging_init()?

The main problem is that the total fixmap size is only around 900kb,
and we want to reserve at least 64kb per cpu for kmap_atomic.
If you want to fit multiple 128kb mappings in there, you run out of
space really fast.

> > Extending the iotable mechanism on ARM would be the convenient
> > solution for us I think.
> Could that easily be extended to give similar semantics sufficiently
> that we can progress with merging more of the UEFI and ACPI support 
> together as common code with x86/ia64?

I don't know what the requirements are, but the idea with iotable
is that the mappings stay around at run time, while it seems you want
to discard them at some point.


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