Re: [PATCH] drm/i915: paper over missed irq issues with force wake vodoo

[Ben Widawsky <ben@bwidawsk.net>]

On 01/10/2012 08:44 PM, Keith Packard wrote:
> On Tue, 10 Jan 2012 16:51:08 -0800, Eric Anholt <eric@anholt.net> wrote:
> 
>> So they've gone out of their way to build broken stuff.  Awesome.
> 
> Well, in theory, the interrupt would be generated *before* the hardware
> goes to RC6; when idle, I'm not exactly sure what the hardware would be
> doing to generate interrupts.

That's right. I think we need to think about the programming sequence a
bit more. The GT should be smart enough to not sleep if it has any work
pending that may generate interrupts. I don't think this by itself
explans anything.

> 
>> I'd say you've found the clue here -- I'm a lot happier with going with
>> your patches now (and I was pretty happy with the gen7 side before).
>> I'd just like to not mess with gen6 unless we've got missed irq bugs
>> there to fix.
> 
> Yeah, knowing that there might be interrupt funnies due to RC6 goes some
> way to explaining why just avoiding RC6 helps.
> 
> I wonder if any of this might explain the RC6 issues we see on SNB on
> some hardware, and whether we should give this a try... I know, grasping
> at straws, but still, it's about all we have at this point.
> 
Just as a reminder, never going into rc6 never fixed any problems, so I
still believe this is somehow timing related.

~Ben the pessimist