linux-kernel - [PATCH V7 3/6] arm64/perf: Add branch stack support in struct arm

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Message-Id: <20230105031039.207972-4-anshuman.khandual@arm.com>
Date:   Thu,  5 Jan 2023 08:40:36 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: [PATCH V7 3/6] arm64/perf: Add branch stack support in struct arm_pmu

This updates 'struct arm_pmu' for branch stack sampling support later. This
adds a new 'features' element in the structure to track supported features,
and another 'private' element to encapsulate implementation attributes on a
given 'struct arm_pmu'. These updates here will help in tracking any branch
stack sampling support, which is being added later. This also adds a helper
arm_pmu_branch_stack_supported().

This also enables perf branch stack sampling event on all 'struct arm pmu',
supporting the feature but after removing the current gate that blocks such
events unconditionally in armpmu_event_init(). Instead a quick probe can be
initiated via arm_pmu_branch_stack_supported() to ascertain the support.

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
 drivers/perf/arm_pmu.c       | 3 +--
 include/linux/perf/arm_pmu.h | 9 +++++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 14a3ed3bdb0b..a85b2d67022e 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -510,8 +510,7 @@ static int armpmu_event_init(struct perf_event *event)
 		!cpumask_test_cpu(event->cpu, &armpmu->supported_cpus))
 		return -ENOENT;
 
-	/* does not support taken branch sampling */
-	if (has_branch_stack(event))
+	if (has_branch_stack(event) && !arm_pmu_branch_stack_supported(armpmu))
 		return -EOPNOTSUPP;
 
 	return __hw_perf_event_init(event);
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 2a9d07cee927..64e1b2594025 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -80,11 +80,14 @@ enum armpmu_attr_groups {
 	ARMPMU_NR_ATTR_GROUPS
 };
 
+#define ARM_PMU_BRANCH_STACK	BIT(0)
+
 struct arm_pmu {
 	struct pmu	pmu;
 	cpumask_t	supported_cpus;
 	char		*name;
 	int		pmuver;
+	int		features;
 	irqreturn_t	(*handle_irq)(struct arm_pmu *pmu);
 	void		(*enable)(struct perf_event *event);
 	void		(*disable)(struct perf_event *event);
@@ -119,8 +122,14 @@ struct arm_pmu {
 
 	/* Only to be used by ACPI probing code */
 	unsigned long acpi_cpuid;
+	void		*private;
 };
 
+static inline bool arm_pmu_branch_stack_supported(struct arm_pmu *armpmu)
+{
+	return armpmu->features & ARM_PMU_BRANCH_STACK;
+}
+
 #define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))
 
 u64 armpmu_event_update(struct perf_event *event);
-- 
2.25.1