linux-kernel - [RFC 1/9] RISC-V: Define a helper function to probe number of hardware counters

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Date:   Mon, 18 Jul 2022 10:01:57 -0700
From:   Atish Patra <atishp@...osinc.com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atishp@...osinc.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Guo Ren <guoren@...nel.org>, kvm-riscv@...ts.infradead.org,
        kvm@...r.kernel.org, linux-riscv@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Will Deacon <will@...nel.org>
Subject: [RFC  1/9] RISC-V: Define a helper function to probe number of hardware counters

KVM module needs to know how many hardware counters the platform supports.
Otherwise, it will not be able to show optimal value of virtual
counters to the guest.

Signed-off-by: Atish Patra <atishp@...osinc.com>
---
 drivers/perf/riscv_pmu_sbi.c   | 23 +++++++++++++++++------
 include/linux/perf/riscv_pmu.h |  4 ++++
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
index 24124546844c..1723af68ffa1 100644
--- a/drivers/perf/riscv_pmu_sbi.c
+++ b/drivers/perf/riscv_pmu_sbi.c
@@ -27,6 +27,7 @@
  */
 static union sbi_pmu_ctr_info *pmu_ctr_list;
 static unsigned int riscv_pmu_irq;
+static struct riscv_pmu *rvpmu;
 
 struct sbi_pmu_event_data {
 	union {
@@ -227,6 +228,12 @@ static const struct sbi_pmu_event_data pmu_cache_event_map[PERF_COUNT_HW_CACHE_M
 	},
 };
 
+int riscv_pmu_sbi_get_num_hw_ctrs(void)
+{
+	return rvpmu ? rvpmu->num_hw_counters : 0;
+}
+EXPORT_SYMBOL(riscv_pmu_sbi_get_num_hw_ctrs);
+
 static int pmu_sbi_ctr_get_width(int idx)
 {
 	return pmu_ctr_list[idx].width;
@@ -443,7 +450,7 @@ static int pmu_sbi_find_num_ctrs(void)
 		return sbi_err_map_linux_errno(ret.error);
 }
 
-static int pmu_sbi_get_ctrinfo(int nctr)
+static int pmu_sbi_get_ctrinfo(int nctr, int *num_hw_ctrs)
 {
 	struct sbiret ret;
 	int i, num_hw_ctr = 0, num_fw_ctr = 0;
@@ -453,7 +460,7 @@ static int pmu_sbi_get_ctrinfo(int nctr)
 	if (!pmu_ctr_list)
 		return -ENOMEM;
 
-	for (i = 0; i <= nctr; i++) {
+	for (i = 0; i < nctr; i++) {
 		ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_GET_INFO, i, 0, 0, 0, 0, 0);
 		if (ret.error)
 			/* The logical counter ids are not expected to be contiguous */
@@ -466,6 +473,7 @@ static int pmu_sbi_get_ctrinfo(int nctr)
 		pmu_ctr_list[i].value = cinfo.value;
 	}
 
+	*num_hw_ctrs = num_hw_ctr;
 	pr_info("%d firmware and %d hardware counters\n", num_fw_ctr, num_hw_ctr);
 
 	return 0;
@@ -698,7 +706,7 @@ static int pmu_sbi_setup_irqs(struct riscv_pmu *pmu, struct platform_device *pde
 static int pmu_sbi_device_probe(struct platform_device *pdev)
 {
 	struct riscv_pmu *pmu = NULL;
-	int num_counters;
+	int num_counters, num_hw_ctrs = 0;
 	int ret = -ENODEV;
 
 	pr_info("SBI PMU extension is available\n");
@@ -713,7 +721,7 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
 	}
 
 	/* cache all the information about counters now */
-	if (pmu_sbi_get_ctrinfo(num_counters))
+	if (pmu_sbi_get_ctrinfo(num_counters, &num_hw_ctrs))
 		goto out_free;
 
 	ret = pmu_sbi_setup_irqs(pmu, pdev);
@@ -723,6 +731,7 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
 		pmu->pmu.capabilities |= PERF_PMU_CAP_NO_EXCLUDE;
 	}
 	pmu->num_counters = num_counters;
+	pmu->num_hw_counters = num_hw_ctrs;
 	pmu->ctr_start = pmu_sbi_ctr_start;
 	pmu->ctr_stop = pmu_sbi_ctr_stop;
 	pmu->event_map = pmu_sbi_event_map;
@@ -733,14 +742,16 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
 
 	ret = cpuhp_state_add_instance(CPUHP_AP_PERF_RISCV_STARTING, &pmu->node);
 	if (ret)
-		return ret;
+		goto out_free;
 
 	ret = perf_pmu_register(&pmu->pmu, "cpu", PERF_TYPE_RAW);
 	if (ret) {
 		cpuhp_state_remove_instance(CPUHP_AP_PERF_RISCV_STARTING, &pmu->node);
-		return ret;
+		goto out_free;
 	}
 
+	rvpmu = pmu;
+
 	return 0;
 
 out_free:
diff --git a/include/linux/perf/riscv_pmu.h b/include/linux/perf/riscv_pmu.h
index 46f9b6fe306e..fc47167e000c 100644
--- a/include/linux/perf/riscv_pmu.h
+++ b/include/linux/perf/riscv_pmu.h
@@ -46,6 +46,7 @@ struct riscv_pmu {
 	irqreturn_t	(*handle_irq)(int irq_num, void *dev);
 
 	int		num_counters;
+	int		num_hw_counters;
 	u64		(*ctr_read)(struct perf_event *event);
 	int		(*ctr_get_idx)(struct perf_event *event);
 	int		(*ctr_get_width)(int idx);
@@ -69,6 +70,9 @@ void riscv_pmu_legacy_skip_init(void);
 static inline void riscv_pmu_legacy_skip_init(void) {};
 #endif
 struct riscv_pmu *riscv_pmu_alloc(void);
+#ifdef CONFIG_RISCV_PMU_SBI
+int riscv_pmu_sbi_get_num_hw_ctrs(void);
+#endif
 
 #endif /* CONFIG_RISCV_PMU */
 
-- 
2.25.1