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@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Tested-by: James Clark <redacted>
Signed-off-by: Anshuman Khandual <redacted>
---
 drivers/perf/arm_pmu.c       |  3 +--
 include/linux/perf/arm_pmu.h | 12 +++++++++++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index aada47e3b126..d4a4f2bd89a5 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 f7fbd162ca4c..0da745eaf426 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h

@@ -102,7 +102,9 @@ struct arm_pmu {
 	int		(*map_event)(struct perf_event *event);
 	void		(*sched_task)(struct perf_event_pmu_context *pmu_ctx, bool sched_in);
 	int		num_events;
-	bool		secure_access; /* 32-bit ARM only */
+	unsigned int	secure_access	: 1, /* 32-bit ARM only */
+			has_branch_stack: 1, /* 64-bit ARM only */
+			reserved	: 30;
 #define ARMV8_PMUV3_MAX_COMMON_EVENTS		0x40
 	DECLARE_BITMAP(pmceid_bitmap, ARMV8_PMUV3_MAX_COMMON_EVENTS);
 #define ARMV8_PMUV3_EXT_COMMON_EVENT_BASE	0x4000

@@ -118,8 +120,16 @@ struct arm_pmu {
 
 	/* Only to be used by ACPI probing code */
 	unsigned long acpi_cpuid;
+
+	/* Implementation specific attributes */
+	void		*private;
 };
 
+static inline bool arm_pmu_branch_stack_supported(struct arm_pmu *armpmu)
+{
+	return armpmu->has_branch_stack;
+}