From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH 2/4] drm/i915: don't disable ERR_INT on the
 IRQ handler
Date: Fri, 20 Sep 2013 10:08:45 +0200
Message-ID: <20130920080845.GH32145@phenom.ffwll.local>
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To: Chris Wilson <chris@chris-wilson.co.uk>, Paulo Zanoni <przanoni@gmail.com>, intel-gfx@lists.freedesktop.org, Paulo Zanoni <paulo.r.zanoni@intel.com>
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On Thu, Sep 19, 2013 at 09:18:24PM +0100, Chris Wilson wrote:
> On Thu, Sep 19, 2013 at 05:00:36PM -0300, Paulo Zanoni wrote:
> > From: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > 
> > We currently disable the ERR_INT interrupts while running the IRQ
> > handler because we fear that if we do an unclaimed register access
> > from inside the IRQ handler we'll keep triggering the IRQ handler
> > forever.
> > 
> > The problem is that since we always disable the ERR_INT interrupts at
> > the IRQ handler, when we get a FIFO underrun we'll always print both
> > messages:
> >   - "uncleared fifo underrun on pipe A"
> >   - "Pipe A FIFO underrun"
> > 
> > Because the "was_enabled" variable from
> > ivybridge_set_fifo_underrun_reporting will always be false (since we
> > disable ERR int at the IRQ handler!).
> > 
> > Instead of actually fixing ivybridge_set_fifo_underrun_reporting,
> > let's just remove the "disable ERR_INT during the IRQ handler" code.
> > As far as we know we shouldn't really be triggering ERR_INT interrupts
> > from the IRQ handler, so if we ever get stuck in the endless loop of
> > interrupts we can git-bisect and revert (and we can even bisect and
> > revert this patch in case I'm just wrong). As a bonus, our IRQ handler
> > is now simpler and a few nanoseconds faster.
> > 
> > Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> 
> One could argue that by unmasking the err interrupt we prevent bugs
> creeping into the interrupt handler.
> 
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

Queued for -next, thanks for the patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch