perf/x86/amd: Make Zen3 branch sampling opt-in

Add a kernel config option CONFIG_PERF_EVENTS_AMD_BRS
to make the support for AMD Zen3 Branch Sampling (BRS) an opt-in
compile time option.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220322221517.2510440-8-eranian@google.com

Author: Stephane Eranian

arch/x86/events/Kconfig

@@ -44,4 +44,12 @@ config PERF_EVENTS_AMD_UNCORE
 
 	  To compile this driver as a module, choose M here: the
 	  module will be called 'amd-uncore'.
+
+config PERF_EVENTS_AMD_BRS
+	depends on PERF_EVENTS && CPU_SUP_AMD
+	bool "AMD Zen3 Branch Sampling support"
+	help
+	  Enable AMD Zen3 branch sampling support (BRS) which samples up to
+	  16 consecutive taken branches in registers.
+
 endmenu

arch/x86/events/amd/Makefile

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
-obj-$(CONFIG_CPU_SUP_AMD)		+= core.o brs.o
+obj-$(CONFIG_CPU_SUP_AMD)		+= core.o
+obj-$(CONFIG_PERF_EVENTS_AMD_BRS)	+= brs.o
 obj-$(CONFIG_PERF_EVENTS_AMD_POWER)	+= power.o
 obj-$(CONFIG_X86_LOCAL_APIC)		+= ibs.o
 obj-$(CONFIG_PERF_EVENTS_AMD_UNCORE)	+= amd-uncore.o

arch/x86/events/perf_event.h

@@ -1218,6 +1218,8 @@ static inline bool fixed_counter_disabled(int i, struct pmu *pmu)
 #ifdef CONFIG_CPU_SUP_AMD
 
 int amd_pmu_init(void);
+
+#ifdef CONFIG_PERF_EVENTS_AMD_BRS
 int amd_brs_init(void);
 void amd_brs_disable(void);
 void amd_brs_enable(void);
@@ -1252,25 +1254,52 @@ static inline void amd_pmu_brs_del(struct perf_event *event)
 
 void amd_pmu_brs_sched_task(struct perf_event_context *ctx, bool sched_in);
 
-/*
- * check if BRS is activated on the CPU
- * active defined as it has non-zero users and DBG_EXT_CFG.BRSEN=1
- */
-static inline bool amd_brs_active(void)
+static inline s64 amd_brs_adjust_period(s64 period)
 {
-	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	if (period > x86_pmu.lbr_nr)
+		return period - x86_pmu.lbr_nr;
 
-	return cpuc->brs_active;
+	return period;
+}
+#else
+static inline int amd_brs_init(void)
+{
+	return 0;
 }
+static inline void amd_brs_disable(void) {}
+static inline void amd_brs_enable(void) {}
+static inline void amd_brs_drain(void) {}
+static inline void amd_brs_lopwr_init(void) {}
+static inline void amd_brs_disable_all(void) {}
+static inline int amd_brs_setup_filter(struct perf_event *event)
+{
+	return 0;
+}
+static inline void amd_brs_reset(void) {}
 
-static inline s64 amd_brs_adjust_period(s64 period)
+static inline void amd_pmu_brs_add(struct perf_event *event)
 {
-	if (period > x86_pmu.lbr_nr)
-		return period - x86_pmu.lbr_nr;
+}
+
+static inline void amd_pmu_brs_del(struct perf_event *event)
+{
+}
+
+static inline void amd_pmu_brs_sched_task(struct perf_event_context *ctx, bool sched_in)
+{
+}
 
+static inline s64 amd_brs_adjust_period(s64 period)
+{
 	return period;
 }
 
+static inline void amd_brs_enable_all(void)
+{
+}
+
+#endif
+
 #else /* CONFIG_CPU_SUP_AMD */
 
 static inline int amd_pmu_init(void)