Re: [Patch 5/5] multiple ring buffer support, fix a irq enable logic for BSD

[Eric Anholt <eric.anholt@intel.com>]

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On Mon, 19 Apr 2010 09:34:42 +0800, "Zou, Nanhai" <nanhai.zou@intel.com> wrote:
> >>-----Original Message-----
> >>From: Anholt, Eric
> >>Sent: 2010年4月13日 2:29
> >>To: Zou, Nanhai; intel-gfx@lists.freedesktop.org
> >>Subject: Re: [Intel-gfx] [Patch 5/5] multiple ring buffer support, fix a irq
> >>enable logic for BSD
> >>
> >>On Wed, 7 Apr 2010 14:28:39 +0800, "Zou, Nanhai" <nanhai.zou@intel.com> wrote:
> >>> Fix the BSD ring related IRQ logic on Ironlake.
> >>> Without this patch, we sometimes see IRQ lost
> >>> When playing H.264 content.
> >>
> >>This patch looks crazy.  Why do we need to do this?  How did you come up
> >>with it?  What prevents races between IIR clear and IER or IMR enable (if
> >>that's what the IIR clear is about).
> >>
> 
> Yes, it looks a little strange. 
> However HW spec from VCG do says IIR should be cleared before enable and disable interrupt.
> We thought this patch fixed the interrupt lost issue seen when playing movie. But now we found it just make the issue much harder to reproduce, so ignore this patch until we found a real fix.

Before enable, sure, that makes sense -- otherwise you'd trigger an
interrupt right away when you know you don't need it.  But we do
unmasking, not enabling.

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