linux-kernel - Re: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM

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Message-Id: <20101008125803.e5bc7306.akpm@linux-foundation.org>
Date:	Fri, 8 Oct 2010 12:58:03 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Felipe Contreras <felipe.contreras@...il.com>,
	linux-main <linux-kernel@...r.kernel.org>,
	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	Arnd Hannemann <arnd@...dnet.de>,
	Han Jonghun <jonghun79.han@...il.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, Hemant Pedanekar <hemantp@...com>
Subject: Re: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM

On Thu, 7 Oct 2010 20:22:45 +0100
Russell King - ARM Linux <linux@....linux.org.uk> wrote:

> On Thu, Oct 07, 2010 at 12:44:22PM +0300, Felipe Contreras wrote:
> > Many drivers are broken, and there's no alternative in sight. Such a big
> > change should stay as a warning for now, and only later should it
> > actually fail.
> > 
> > The drivers are not doing something correct, we get it, but for now it's
> > better to allow them to work (they do 99% of the time anyway) rather
> > than to force everyone to revert this patch in their internal trees
> > until there's a solution. A slightly broken functionality is better than
> > no functionality at all.
> > 
> > A warning lets people know that what they are doing is not right, and
> > they should fix it.
> 
> So what are _you_ going to do to fix these drivers?  Continue reverting
> this patch?  Or are you just going to ignore the issue entirely?
> 
> Unless people can come up with a plan to fix their drivers using ioremap
> on system RAM thereby violating the architecture specification, I'm
> _not_ going to apply this patch.

We *do* have a plan: as of 2.6.36, the kernel will emit a WARN_ON trace
when a driver does this.  Offending code will be discovered, developers
will get bug reports from worried users, etc.  This is usually pretty
effective.

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