On Thu, 28 Sep 2017 15:09:50 +0100
Will Deacon [off-list ref] 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;

So -ENOENT will make tools/perf/util/evsel.c tell the user "The %s event is not
supported." whereas returning -ENODEV will say "No such device - did
you specify an out-of-range profile CPU?" which may or may not be more
appropriate for this check.

+	if (arm_spe_event_to_pmsevfr(event) & SYS_PMSEVFR_EL1_RES0)
+		return -EOPNOTSUPP;
+	if (attr->exclude_idle)
+		return -EOPNOTSUPP;

"PMU Hardware doesn't support sampling/overflow-interrupts." will be
printed if the user didn't specify a sample period.  Otherwise, a
string with "/bin/dmesg may provide additional information." will be
printed.

I was hoping for a response from acme by now for this:

https://www.spinics.net/lists/linux-perf-users/msg04066.html

Alas, nothing.  Looking at the #ifdef x86 in evsel.c, I'm guessing
it'll be ok, although I'm still not sure how PMU-specific we can get in
evsel.c, nor whether it's ok to communicate lists of h/w supported
sample periods through /sys/bus/event_source/devices/...

acme?  OK to refactor evsel messaging for Arm, including parsing for
which PMUs are being used, so customize the message?

Kim