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

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Message-ID: <AANLkTimDd10oj=rruYcB=qTaWWMAJvSCQAJNi+nQqzp7@mail.gmail.com>
Date:	Sat, 9 Oct 2010 14:59:45 +0300
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Arnd Hannemann <arnd@...dnet.de>,
	Hemant Pedanekar <hemantp@...com>, Greg KH <greg@...ah.com>,
	linux-main <linux-kernel@...r.kernel.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Han Jonghun <jonghun79.han@...il.com>
Subject: Re: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM

2010/10/9 Arnd Bergmann <arnd@...db.de>:
> On Saturday 09 October 2010 12:28:19 Felipe Contreras wrote:
>> Also, what do you think is the right attitude? Do you think all
>> driver writers should follow each and every patch on the mailing list
>> or always try release candidates? Even if they all did (some do),
>> there's no generic solution, so they all are scratching their heads
>> about how to solve this. It might be crystal clear for you how such
>> generic solution could be implemented, or perhaps how some of these
>> drivers can be fixed individually, if so, why don't you come with a
>> proposal to mitigate the pain of fixing such drivers.
>
> Please put this into perspective, it's not like this was ever a
> normal thing to do, and drivers doing an ioremap on kernel memory
> would typically not make it through a review. I've looked through
> the ARM specific drivers that do ioremap and practically all of
> them just map their MMIO registers as they should.
>
> The few drivers that may be hit by this are typically in drivers/staging
> exactly because issues like this have not been fixed yet.
>
> We should probably just fix the non-staging drivers that are hit by
> this now and declare the issue done.
>
> When you say that "many drivers broken", can you list the ones you know
> about? It would probably help resolve this the right way.

I know of tidspbridge, in my original mail I listed some links, one
which mentions: sh_mobile_ceu_camera, maybe i.MX31 users of the
mx3_camera driver: pcm037 and mx31moboard.

http://article.gmane.org/gmane.linux.ports.sh.devel/8560

>From the looks of it, PowerVR SGX seems like it will be broken too:
http://meego.gitorious.org/meego-os-base/kernel-source/trees/master/patches

Other people have been asking questions without mentioning specific drivers too:
http://www.spinics.net/lists/linux-fbdev/msg01745.html

But my guess is that most of the issues would be found after releasing
.36, and of course the current issues cannot possibly be fixed in that
time-frame.

Anyway, Russell said he already reverted the change, which I don't
think is ideal, we need the warning, then I think many more will pop
up.

-- 
Felipe Contreras
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