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Subject[PATCH] drivers/perf: arm_pmu: save/restore cpu cycle counter in cpu_pm_pmu_notify
Date
Sometimes userspace need a high resolution cycle counter by reading
pmccntr_el0.

In commit da4e4f18afe0 ("drivers/perf: arm_pmu: implement CPU_PM
notifier"), it resets all the counters even when the pmcr_el0.E and
pmcntenset_el0.C are both 1 . That is incorrect.

We need to save the registers and counter before CPU_PM_ENTER and
restore them after CPU_PM_EXIT.

Fixes: da4e4f18afe0 ("drivers/perf: arm_pmu: implement CPU_PM notifier")
Signed-off-by: Jia He <jia.he@hxt-semitech.com>
---
drivers/perf/arm_pmu.c | 72 +++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 66 insertions(+), 6 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 7bc5eee..cf55c91 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -26,6 +26,12 @@

#include <asm/irq_regs.h>

+#ifdef CONFIG_CPU_PM
+DEFINE_PER_CPU(u32, saved_pmcr_el0);
+DEFINE_PER_CPU(u32, saved_pmcntenset_el0);
+DEFINE_PER_CPU(u64, saved_cycle_cnter);
+#endif
+
static int
armpmu_map_cache_event(const unsigned (*cache_map)
[PERF_COUNT_HW_CACHE_MAX]
@@ -719,6 +725,15 @@ static void cpu_pm_pmu_setup(struct arm_pmu *armpmu, unsigned long cmd)
}
}

+static int pmc_cycle_counter_enabled(void)
+{
+ if ((read_sysreg(pmcr_el0) & ARMV8_PMU_PMCR_E) &&
+ read_sysreg(pmcntenset_el0) & 1<<31)
+ return 1;
+
+ return 0;
+}
+
static int cpu_pm_pmu_notify(struct notifier_block *b, unsigned long cmd,
void *v)
{
@@ -729,16 +744,53 @@ static int cpu_pm_pmu_notify(struct notifier_block *b, unsigned long cmd,
if (!cpumask_test_cpu(smp_processor_id(), &armpmu->supported_cpus))
return NOTIFY_DONE;

- /*
- * Always reset the PMU registers on power-up even if
- * there are no events running.
- */
- if (cmd == CPU_PM_EXIT && armpmu->reset)
- armpmu->reset(armpmu);
+ if (cmd == CPU_PM_EXIT) {
+ /*
+ * Always reset the PMU registers on power-up even if
+ * there are no events running.
+ */
+ if (armpmu->reset)
+ armpmu->reset(armpmu);
+
+ /*
+ * Restore the saved pmcr_el0 and pmcntenset_el0
+ * if pmc cycle counter is enabled, restore the counter
+ */
+ write_sysreg(get_cpu_var(saved_pmcr_el0), pmcr_el0);
+ write_sysreg(get_cpu_var(saved_pmcntenset_el0),
+ pmcntenset_el0);
+
+ if (pmc_cycle_counter_enabled()) {
+ write_sysreg(get_cpu_var(saved_cycle_cnter),
+ pmccntr_el0);
+ put_cpu_var(saved_cycle_cnter);
+ }
+ put_cpu_var(saved_pmcntenset_el0);
+ put_cpu_var(saved_pmcr_el0);
+ }
+
+ if (cmd == CPU_PM_ENTER) {
+ /* If currently pmc cycle counter is enabled,
+ * save the counter to percpu section
+ */
+ if (pmc_cycle_counter_enabled()) {
+ get_cpu_var(saved_cycle_cnter) = read_sysreg(
+ pmccntr_el0);
+ put_cpu_var(saved_cycle_cnter);
+ }
+
+ get_cpu_var(saved_pmcr_el0) = read_sysreg(pmcr_el0);
+
+ get_cpu_var(saved_pmcntenset_el0) = read_sysreg(
+ pmcntenset_el0);
+ put_cpu_var(saved_pmcntenset_el0);
+ put_cpu_var(saved_pmcr_el0);
+ }

if (!enabled)
return NOTIFY_OK;

+ /* if any hw_events is used */
switch (cmd) {
case CPU_PM_ENTER:
armpmu->stop(armpmu);
@@ -758,7 +810,15 @@ static int cpu_pm_pmu_notify(struct notifier_block *b, unsigned long cmd,

static int cpu_pm_pmu_register(struct arm_pmu *cpu_pmu)
{
+ int i;
cpu_pmu->cpu_pm_nb.notifier_call = cpu_pm_pmu_notify;
+
+ for_each_possible_cpu(i) {
+ per_cpu(saved_pmcr_el0, i) = 0;
+ per_cpu(saved_pmcntenset_el0, i) = 0;
+ per_cpu(saved_cycle_cnter, i) = 0;
+ }
+
return cpu_pm_register_notifier(&cpu_pmu->cpu_pm_nb);
}

--
2.7.4
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