[RFC] Prohibit ioremap() on kernel managed RAM

[George G. Davis]

Hi,

On Fri, Apr 23, 2010 at 03:40:58PM +0100, Russell King wrote:
> > Above change is necessary but what an alternative approach is for this. 
> > There are many use case where ioremap* is needed.
> 
> This is a very difficult issue to answer; the only way we can safely
> remap RAM with different attributes is if we disable the existing
> mappings - but since we create those with 1MB sections, that's far
> from easy to achieve.
> 
> I think a viable safe solution is to set aside some RAM at boot (which
> the kernel doesn't manage at all) and then use ioremap on that; that
> approach will still work with this patch in place.

So cases such as the omapfb driver which use reserve_bootmem() (in
arch/arm/plat-omap/fb.c) and then later use ioremap_wc() to remap
reserved memory (in drivers/video/omap2/omapfb/omapfb-main.c)
will no longer work with this change.

Is that correct?

Thanks!

--
Regards,
George