From mboxrd@z Thu Jan  1 00:00:00 1970
From: gdavis@mvista.com (George G. Davis)
Date: Fri, 30 Apr 2010 12:33:56 -0400
Subject: [RFC] Prohibit ioremap() on kernel managed RAM
In-Reply-To: <20100423144058.GA11637@ZenIV.linux.org.uk>
References: <20100423144058.GA11637@ZenIV.linux.org.uk>
Message-ID: <20100430163356.GV2619@mvista.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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