[PATCH 1/3] drivers/perf: hisi_pcie: Record hardware counts correctly

[Yicong Yang]

From: Yicong Yang <yangyicong at hisilicon.com>

Currently we set the period and record it as the initial value of the
counter without checking it's set to the hardware successfully or not.
However the counter maybe unwritable if the target event is unsupported
by the device. In such case we will pass user a wrong count:

[start counts when setting the period]
hwc->prev_count = 0x8000000000000000
device.counter_value = 0 // the counter is not set as the period
[when user reads the counter]
event->count = device.counter_value - hwc->prev_count
             = 0x8000000000000000 // wrong. should be 0.

Fix this by record the hardware counter counts correctly when setting
the period.

Fixes: 8404b0fbc7fb ("drivers/perf: hisi: Add driver for HiSilicon PCIe PMU")
Signed-off-by: Yicong Yang <yangyicong at hisilicon.com>
---
 drivers/perf/hisilicon/hisi_pcie_pmu.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/perf/hisilicon/hisi_pcie_pmu.c b/drivers/perf/hisilicon/hisi_pcie_pmu.c
index f06027574a24..fba569a8640c 100644
--- a/drivers/perf/hisilicon/hisi_pcie_pmu.c
+++ b/drivers/perf/hisilicon/hisi_pcie_pmu.c
@@ -452,10 +452,24 @@ static void hisi_pcie_pmu_set_period(struct perf_event *event)
 	struct hisi_pcie_pmu *pcie_pmu = to_pcie_pmu(event->pmu);
 	struct hw_perf_event *hwc = &event->hw;
 	int idx = hwc->idx;
+	u64 orig_cnt, cnt;
+
+	orig_cnt = hisi_pcie_pmu_read_counter(event);
 
 	local64_set(&hwc->prev_count, HISI_PCIE_INIT_VAL);
 	hisi_pcie_pmu_writeq(pcie_pmu, HISI_PCIE_CNT, idx, HISI_PCIE_INIT_VAL);
 	hisi_pcie_pmu_writeq(pcie_pmu, HISI_PCIE_EXT_CNT, idx, HISI_PCIE_INIT_VAL);
+
+	/*
+	 * The counter maybe unwritable if the target event is unsupported.
+	 * Check this by comparing the counts after setting the period. If
+	 * the counts stay unchanged after setting the period then update
+	 * the hwc->prev_count correctly. Otherwise the final counts user
+	 * get maybe totally wrong.
+	 */
+	cnt = hisi_pcie_pmu_read_counter(event);
+	if (orig_cnt == cnt)
+		local64_set(&hwc->prev_count, cnt);
 }
 
 static void hisi_pcie_pmu_enable_counter(struct hisi_pcie_pmu *pcie_pmu, struct hw_perf_event *hwc)
-- 
2.24.0