On Wed, 15 Jan 2014, Will Deacon wrote:
> Hi Vince,
>
> On Tue, Jan 14, 2014 at 04:42:13AM +0000, Vince Weaver wrote:
> > On Fri, 10 Jan 2014, Will Deacon wrote:
> > > In the absence of a core change, I think I'd rather have something like
> > > your
> > > second patch, but without the extra no_overflow_irq field (you can check
> > > the
> > > platform device, as I mentioned previously).
> >
> > Something like the following? It works on my rasp-pi, still waiting for
> > the compile to finish on the pandaboard so I haven't verified that the
> > has-working-interrupt case still works.
>
> [...]
>
> > diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
> > index bc3f2ef..e2c4aa2 100644
> > --- a/arch/arm/kernel/perf_event.c
> > +++ b/arch/arm/kernel/perf_event.c
> > @@ -397,7 +397,7 @@ __hw_perf_event_init(struct perf_event *event)
> > */
> > hwc->config_base |= (unsigned long)mapping;
> >
> > - if (!hwc->sample_period) {
> > + if (!is_sampling_event(event)) {
> > /*
> > * For non-sampling runs, limit the sample_period to half
> > * of the counter width. That way, the new counter value
> > @@ -407,6 +407,14 @@ __hw_perf_event_init(struct perf_event *event)
> > hwc->sample_period = armpmu->max_period >> 1;
> > hwc->last_period = hwc->sample_period;
> > local64_set(&hwc->period_left, hwc->sample_period);
> > + } else {
> > +
> > + /*
> > + * If we have no PMU interrupt we cannot sample.
> > + */
> > + if (platform_get_irq(armpmu->plat_device, 0) < 0)
> > + return -EOPNOTSUPP;
>
> I think this should be <= 0, but apart from that this looks alright to me in
> the absence of a core change.
It's a shame platform_get_irq() doesn't have better documentation.
I always forget what the result of the "is 0 a valid IRQ" flamewar was.
A grep through the kernel shows more or less an even split of using !,
using <0, and using <=0.
I'll put together a patch with this change and send it off. I'm also
investigating the proper core change, but I'm guessing that's going to
take a bit longer to get together, and it would be nice to have the
rasp-pi counters working sooner rather than later.
Vince
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