[PATCH v2 2/5] arm64: cpufeature: Add feature to detect heterogeneous systems

[Raphael Gault]

This feature is required in order to enable PMU counters direct
access from userspace only when the system is homogeneous.
This feature checks the model of each CPU brought online and compares it
to the boot CPU. If it differs then it is heterogeneous.

Cc: suzuki.poul...@arm.com

Signed-off-by: Raphael Gault <raphael.ga...@arm.com>
---
 arch/arm64/include/asm/cpucaps.h |  3 ++-
 arch/arm64/kernel/cpufeature.c   | 20 ++++++++++++++++++++
 arch/arm64/kernel/perf_event.c   |  1 +
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index f19fe4b9acc4..040370af38ad 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -52,7 +52,8 @@
 #define ARM64_HAS_IRQ_PRIO_MASKING             42
 #define ARM64_HAS_DCPODP                       43
 #define ARM64_WORKAROUND_1463225               44
+#define ARM64_HAS_HETEROGENEOUS_PMU            45
 
-#define ARM64_NCAPS                            45
+#define ARM64_NCAPS                            46
 
 #endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index f29f36a65175..3527f329ba1a 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1248,6 +1248,15 @@ static bool can_use_gic_priorities(const struct 
arm64_cpu_capabilities *entry,
 }
 #endif
 
+static bool has_heterogeneous_pmu(const struct arm64_cpu_capabilities *entry,
+                                    int scope)
+{
+       u32 model = read_cpuid_id() & MIDR_CPU_MODEL_MASK;
+       struct cpuinfo_arm64 *boot = &per_cpu(cpu_data, 0);
+
+       return  (boot->reg_midr & MIDR_CPU_MODEL_MASK) != model;
+}
+
 static const struct arm64_cpu_capabilities arm64_features[] = {
        {
                .desc = "GIC system register CPU interface",
@@ -1548,6 +1557,16 @@ static const struct arm64_cpu_capabilities 
arm64_features[] = {
                .min_field_value = 1,
        },
 #endif
+       {
+               /*
+                * Detect whether the system is heterogeneous or
+                * homogeneous
+                */
+               .desc = "Detect whether we have heterogeneous CPUs",
+               .capability = ARM64_HAS_HETEROGENEOUS_PMU,
+               .type = ARM64_CPUCAP_SCOPE_LOCAL_CPU | 
ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU,
+               .matches = has_heterogeneous_pmu,
+       },
        {},
 };
 
@@ -1715,6 +1734,7 @@ static void __init setup_elf_hwcaps(const struct 
arm64_cpu_capabilities *hwcaps)
                        cap_set_elf_hwcap(hwcaps);
 }
 
+
 static void update_cpu_capabilities(u16 scope_mask)
 {
        int i;
diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 96e90e270042..24575c0a0065 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -19,6 +19,7 @@
 #include <linux/of.h>
 #include <linux/perf/arm_pmu.h>
 #include <linux/platform_device.h>
+#include <linux/smp.h>
 
 /* ARMv8 Cortex-A53 specific event types. */
 #define ARMV8_A53_PERFCTR_PREF_LINEFILL                                0xC2
-- 
2.17.1