linux-kernel - Re: DRM Error on Acer Aspire One

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Message-Id: <20100511155600.5c416992.akpm@linux-foundation.org>
Date:	Tue, 11 May 2010 15:56:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dave Airlie <airlied@...il.com>
Cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	Jaswinder Singh Rajput <jaswinderlinux@...il.com>,
	dri-devel@...ts.freedesktop.org, Dave Airlie <airlied@...ux.ie>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Keith Packard <keithp@...thp.com>,
	Eric Anholt <eric@...olt.net>, Ingo Molnar <mingo@...e.hu>
Subject: Re: DRM Error on Acer Aspire One

On Wed, 12 May 2010 08:51:05 +1000
Dave Airlie <airlied@...il.com> wrote:

> On Wed, May 12, 2010 at 8:32 AM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> > On Wed, 12 May 2010 08:22:49 +1000
> > Dave Airlie <airlied@...il.com> wrote:
> >
> >> On Wed, May 12, 2010 at 5:57 AM, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> >> > On Tue, 11 May 2010 12:10:01 -0700, Andrew Morton <akpm@...ux-foundation.org> wrote:
> >> >> On Tue, 11 May 2010 19:52:31 +0100
> >> >> Chris Wilson <chris@...is-wilson.co.uk> wrote:
> >> >>
> >> >> > On Tue, 11 May 2010 11:35:55 -0400, Andrew Morton <akpm@...ux-foundation.org> wrote:
> >> >> > > No, io_mapping_map_atomic_wc() cannot be used from [soft]irq context:
> >> >> > > it hardwires use of KM_USER0. __I suggest that io_mapping_create_wc(),
> >> >> > > io_mapping_map_atomic_wc() etc be changed so that the caller passes in the
> >> >> > > KM_foo kmap slot index.
> >> >> >
> >> >> > Argh, sorry for the noise, read the mail in the wrong order. Thanks for
> >> >> > the review. It would be sensible to go with your simpler patch whilst
> >> >> > io_mapping_map_atomic_wc() is improved.
> >> >>
> >> >> OK. __I'll be sending a bunch of fixes Linuswards in an hour or two.
> >> >> Should I include this?
> >> >
> >> > Yes.
> >> >
> >> > Acked-by: Chris Wilson <chris@...is-wilson.co.uk>
> >> >
> >>
> >> I'm not sure pushing this in at this point is a good idea, if I'm
> >> reading it correctly we've no idea what KM_IRQ is being used for,
> >
> > It's used for taking kmaps from IRQ contexts.
> >
> >> and
> >> this codepath is called from non-irq contexts just as much as irq
> >> contexts.
> >
> > That's fine. __As long as we do a local_irq_disable(), KM_IRQ0 can be
> > used from both irq- and non-irq contexts. __All we need to do is to
> > ensure that some interrupt cannot come along on this CPU and corrupt
> > the slot.
> 
> I don't think we do that in a lot of places, and I'd rather not add
> that in to fix this problem at this point in the release cycle, as
> we've no idea what it might break/regress.

What is "that"?  The switch to irq-protected KM_IRQ0?  That won't break
anything.

> Its easier to just disable the hangcheck copy and try again for 2.6.35
> with a workqueue or slow work.

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