From: gdavis@mvista•com (George G. Davis)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC] Prohibit ioremap() on kernel managed RAM
Date: Mon, 3 May 2010 11:59:00 -0400 [thread overview]
Message-ID: <20100503155900.GA26552@mvista.com> (raw)
In-Reply-To: <1272645511.22683.1.camel@e102109-lin.cambridge.arm.com>
Hi,
On Fri, Apr 30, 2010 at 05:38:31PM +0100, Catalin Marinas wrote:
> On Fri, 2010-04-30 at 17:33 +0100, George G. Davis wrote:
> > 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.
>
> Another solution would be to allow the unmapping of sections from the
> kernel linear mapping. I think x86 does this already for the AGP
> aperture.
I've yet to grok that code but have been curious about how this is done
for x86 graphics. : )
--
Regards,
George
>
> --
> Catalin
next prev parent reply other threads:[~2010-05-03 15:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-23 14:40 [RFC] Prohibit ioremap() on kernel managed RAM Russell King
2010-04-30 16:33 ` George G. Davis
2010-04-30 16:38 ` Catalin Marinas
2010-05-01 6:24 ` Shilimkar, Santosh
2010-05-01 9:19 ` Russell King - ARM Linux
2010-05-03 15:59 ` George G. Davis [this message]
2010-05-04 15:29 ` Catalin Marinas
2010-05-05 16:23 ` George G. Davis
2010-05-05 16:30 ` Russell King - ARM Linux
2010-05-05 16:33 ` George G. Davis
2010-04-30 18:19 ` Russell King - ARM Linux
2010-04-30 22:30 ` George G. Davis
-- strict thread matches above, loose matches on Subject: below --
2010-04-08 9:48 Russell King - ARM Linux
2010-04-23 14:15 ` Catalin Marinas
2010-04-23 14:27 ` Shilimkar, Santosh
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