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SubjectRe: [PATCH v4 4/5] drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension
On Mon, Jun 05, 2017 at 10:55:16AM -0500, Kim Phillips wrote:
> On Mon, 5 Jun 2017 16:22:56 +0100
> Will Deacon <will.deacon@arm.com> wrote:
>
> > +/* Perf callbacks */
> > +static int arm_spe_pmu_event_init(struct perf_event *event)
> > +{
> > + u64 reg;
> > + struct perf_event_attr *attr = &event->attr;
> > + struct arm_spe_pmu *spe_pmu = to_spe_pmu(event->pmu);
> > +
> > + /* This is, of course, deeply driver-specific */
> > + if (attr->type != event->pmu->type)
> > + return -ENOENT;
> > +
> > + if (event->cpu >= 0 &&
> > + !cpumask_test_cpu(event->cpu, &spe_pmu->supported_cpus))
> > + return -ENOENT;
> > +
> > + if (arm_spe_event_to_pmsevfr(event) & PMSEVFR_EL1_RES0)
> > + return -EOPNOTSUPP;
> > +
> > + if (event->hw.sample_period < spe_pmu->min_period ||
> > + event->hw.sample_period & PMSIRR_EL1_IVAL_MASK)
> > + return -EOPNOTSUPP;
> > +
> > + if (attr->exclude_idle)
> > + return -EOPNOTSUPP;
> > +
> > + /*
> > + * Feedback-directed frequency throttling doesn't work when we
> > + * have a buffer of samples. We'd need to manually count the
> > + * samples in the buffer when it fills up and adjust the event
> > + * count to reflect that. Instead, force the user to specify a
> > + * sample period instead.
> > + */
> > + if (attr->freq)
> > + return -EINVAL;
> > +
> > + reg = arm_spe_event_to_pmsfcr(event);
> > + if ((reg & BIT(PMSFCR_EL1_FE_SHIFT)) &&
> > + !(spe_pmu->features & SPE_PMU_FEAT_FILT_EVT))
> > + return -EOPNOTSUPP;
> > +
> > + if ((reg & BIT(PMSFCR_EL1_FT_SHIFT)) &&
> > + !(spe_pmu->features & SPE_PMU_FEAT_FILT_TYP))
> > + return -EOPNOTSUPP;
> > +
> > + if ((reg & BIT(PMSFCR_EL1_FL_SHIFT)) &&
> > + !(spe_pmu->features & SPE_PMU_FEAT_FILT_LAT))
> > + return -EOPNOTSUPP;
> > +
> > + return 0;
> > +}
>
> AFAICT, my comments from the last submission have still not been fully
> addressed:
>
> http://lists.infradead.org/pipermail/linux-arm-kernel/2017-May/508027.html

To be frank, I really don't plan to address them and, even if I did, I would
trust Mark to NAK the change. If you're desperate for pr_debug, I'll add it
to keep you happy, but anything more than that needs to come in the form of
a separate patch submission addressing the wider problem of error reporting
from PMU drivers back to userspace. Patches welcome, but I suspect you're
still busy working on the tools code.

Do you have any constructive comments on the patch?

Will

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