Re: [PATCH v3 2/4] drm/i915/pmu: Use kstat_irqs to get interrupt count

[Jarkko Sakkinen <jarkko@kernel.org>]

On Sun, Dec 06, 2020 at 10:33:09PM +0100, Thomas Gleixner wrote:
> On Sun, Dec 06 2020 at 17:38, Thomas Gleixner wrote:
> > On Fri, Dec 04 2020 at 18:43, Jerry Snitselaar wrote:
> >> Now that kstat_irqs is exported, get rid of count_interrupts in
> >> i915_pmu.c
> >
> > May I ask why this has been merged in the first place?
> >
> > Nothing in a driver has ever to fiddle with the internals of an irq
> > descriptor. We have functions for properly accessing them. Just because
> > C allows to fiddle with everything is not a justification. If the
> > required function is not exported then adding the export with a proper
> > explanation is not asked too much.
> >
> > Also this lacks protection or at least a comment why this can be called
> > safely and is not subject to a concurrent removal of the irq descriptor.
> > The same problem exists when calling kstat_irqs(). It's even documented
> > at the top of the function.
> 
> And as pointed out vs. that TPM thing this really could have been a
> trivial
> 
>     i915->irqs++;
> 
> in the interrupt handler and a read of that instead of iterating over
> all possible cpus and summing it up. Oh well...

I'm fine with that. 

> Thanks,
> 
>         tglx

/Jarkko