[PATCH 3/6] arm64: pmu: Add function implementation to update event index in userpage.

[Raphael Gault]

In order to be able to access the counter directly for userspace,
we need to provide the index of the counter using the userpage.
We thus need to override the event_idx function to retrieve and
convert the perf_event index to armv8 hardware index.

Signed-off-by: Raphael Gault <raphael.gault@xxxxxxx>
---
 arch/arm64/kernel/perf_event.c |  4 ++++
 drivers/perf/arm_pmu.c         | 10 ++++++++++
 include/linux/perf/arm_pmu.h   |  2 ++
 3 files changed, 16 insertions(+)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 6164d389eed6..e6316f99f66b 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -890,6 +890,8 @@ static int __armv8_pmuv3_map_event(struct perf_event *event,
 	if (armv8pmu_event_is_64bit(event))
 		event->hw.flags |= ARMPMU_EVT_64BIT;
 
+	event->hw.flags |= ARMPMU_EL0_RD_CNTR;
+
 	/* Only expose micro/arch events supported by this PMU */
 	if ((hw_event_id > 0) && (hw_event_id < ARMV8_PMUV3_MAX_COMMON_EVENTS)
 	    && test_bit(hw_event_id, armpmu->pmceid_bitmap)) {
@@ -1188,6 +1190,8 @@ void arch_perf_update_userpage(struct perf_event *event,
 	 */
 	freq = arch_timer_get_rate();
 	userpg->cap_user_time = 1;
+	userpg->cap_user_rdpmc =
+		!!(event->hw.flags & ARMPMU_EL0_RD_CNTR);
 
 	clocks_calc_mult_shift(&userpg->time_mult, &shift, freq,
 			NSEC_PER_SEC, 0);
diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index eec75b97e7ea..3f4c2ec7ff89 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -777,6 +777,15 @@ static void cpu_pmu_destroy(struct arm_pmu *cpu_pmu)
 					    &cpu_pmu->node);
 }
 
+
+static int armpmu_event_idx(struct perf_event *event)
+{
+	if (!(event->hw.flags & ARMPMU_EL0_RD_CNTR))
+		return 0;
+
+	return event->hw.idx;
+}
+
 static struct arm_pmu *__armpmu_alloc(gfp_t flags)
 {
 	struct arm_pmu *pmu;
@@ -803,6 +812,7 @@ static struct arm_pmu *__armpmu_alloc(gfp_t flags)
 		.start		= armpmu_start,
 		.stop		= armpmu_stop,
 		.read		= armpmu_read,
+		.event_idx	= armpmu_event_idx,
 		.filter_match	= armpmu_filter_match,
 		.attr_groups	= pmu->attr_groups,
 		/*
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 4641e850b204..3bef390c1069 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -30,6 +30,8 @@
  */
 /* Event uses a 64bit counter */
 #define ARMPMU_EVT_64BIT		1
+/* Allow access to hardware counter from userspace */
+#define ARMPMU_EL0_RD_CNTR		2
 
 #define HW_OP_UNSUPPORTED		0xFFFF
 #define C(_x)				PERF_COUNT_HW_CACHE_##_x
-- 
2.17.1