gm45 intel gfx can generate non-MSI irq# in MSI mode (was Re: [PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips (was Re: [3.9-rc1] irq 16: nobody cared (was [3.9-rc1] very poor interrupt respo

[Alan Stern]

On Tue, 19 Mar 2013, Daniel Vetter wrote:

> > That might be misleading.  It's possible that the erroneous IRQs _are_
> > being issued but you're simply not aware of them.  If the kernel thinks
> > that no device is using IRQ 16 then it will leave that IRQ disabled.
> 
> I guess I should have phrased it more precisely, but that's exactly
> what I expect is happening on my machine: I don't have anything on
> irq16 (i.e. in non-msi mode the gfx interrupt isn't shared) and hence
> the irq is completely disabled. Which obviously makes it impossible
> for me to reproduce the issue. To test that theory, is there a quick
> way to force-enable a given interrupt, short of just hacking up a 2nd
> dummy irq handler in my driver?

I don't know of any way.  In fact, I have been thinking of writing a 
test driver module, with a module parameter telling it which IRQ number 
to register for.  It seems like the sort of thing that would be useful 
to have, from time to time.

Alan Stern