[RFC PATCH 2/5] Kernel module: to Enable userspace access to PMU counters for ArmV8

[Yogesh Tillu]

This Patchset is for Kernel Module to Enable userspace access to PMU counters(ArmV8)

Signed-off-by: Yogesh Tillu <yogesh.tillu at linaro.org>
---
 ARMv8_Module/Makefile         |    8 ++++
 ARMv8_Module/README           |    1 +
 ARMv8_Module/enable_arm_pmu.c |   96 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 105 insertions(+)
 create mode 100644 ARMv8_Module/Makefile
 create mode 100644 ARMv8_Module/README
 create mode 100644 ARMv8_Module/enable_arm_pmu.c

diff --git a/ARMv8_Module/Makefile b/ARMv8_Module/Makefile
new file mode 100644
index 0000000..19a31ea
--- /dev/null
+++ b/ARMv8_Module/Makefile
@@ -0,0 +1,8 @@
+obj-m	:= enable_arm_pmu.o
+KDIR	:= /lib/modules/$(shell uname -r)/build
+PWD	:= $(shell pwd)
+
+all:
+	$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
+clean:
+	$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) clean
diff --git a/ARMv8_Module/README b/ARMv8_Module/README
new file mode 100644
index 0000000..648456b
--- /dev/null
+++ b/ARMv8_Module/README
@@ -0,0 +1 @@
+make ARCH=arm64 clean;make ARCH=arm64 CROSS_COMPILE=~/arm64-tc-14.06/bin/aarch64-linux-gnu- -C ~/work/lava_ci/juno/linux-linaro/workspace/builddir-3.16.0-linaro-juno/ SUBDIRS=`pwd`
diff --git a/ARMv8_Module/enable_arm_pmu.c b/ARMv8_Module/enable_arm_pmu.c
new file mode 100644
index 0000000..5c87b08
--- /dev/null
+++ b/ARMv8_Module/enable_arm_pmu.c
@@ -0,0 +1,96 @@
+/*
+ * Enable user-mode ARM performance counter access.
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/smp.h>
+/** -- Configuration stuff ------------------------------------------------- */
+
+#define DRVR_NAME "enable_arm_pmu"
+
+#if !defined(__aarch64__)
+	#error Module can only be compiled on ARM 64 machines.
+#endif
+
+/** -- Initialization & boilerplate ---------------------------------------- */
+
+#define PERF_DEF_OPTS 		(1 | 16)
+#define PERF_OPT_RESET_CYCLES 	(2 | 4)
+#define PERF_OPT_DIV64 		(8)
+#define ARMV8_PMCR_MASK         0x3f
+#define ARMV8_PMCR_E            (1 << 0) /* Enable all counters */
+#define ARMV8_PMCR_P            (1 << 1) /* Reset all counters */
+#define ARMV8_PMCR_C            (1 << 2) /* Cycle counter reset */
+#define ARMV8_PMCR_D            (1 << 3) /* CCNT counts every 64th cpu cycle */
+#define ARMV8_PMCR_X            (1 << 4) /* Export to ETM */
+#define ARMV8_PMCR_DP           (1 << 5) /* Disable CCNT if non-invasive debug*/
+#define ARMV8_PMCR_N_SHIFT      11       /* Number of counters supported */
+#define ARMV8_PMCR_N_MASK       0x1f
+
+#define ARMV8_PMUSERENR_EN_EL0  (1 << 0) /* EL0 access enable */
+#define ARMV8_PMUSERENR_CR      (1 << 2) /* Cycle counter read enable */
+#define ARMV8_PMUSERENR_ER      (1 << 3) /* Event counter read enable */
+
+static inline u32 armv8pmu_pmcr_read(void)
+{
+        u64 val=0;
+        asm volatile("mrs %0, pmcr_el0" : "=r" (val));
+        return (u32)val;
+}
+static inline void armv8pmu_pmcr_write(u32 val)
+{
+        val &= ARMV8_PMCR_MASK;
+        isb();
+        asm volatile("msr pmcr_el0, %0" : : "r" ((u64)val));
+}
+ 
+static void
+enable_cpu_counters(void* data)
+{
+	u32 val=0;
+/* Enable user-mode access to counters. */
+	asm volatile("msr pmuserenr_el0, %0" : : "r"((u64)ARMV8_PMUSERENR_EN_EL0|ARMV8_PMUSERENR_ER|ARMV8_PMUSERENR_CR));
+/* Initialize & Reset PMNC: C and P bits. */
+	armv8pmu_pmcr_write(ARMV8_PMCR_P | ARMV8_PMCR_C); 
+/*G4.4.11
+PMINTENSET, Performance Monitors Interrupt Enable Set register */
+/*cycle counter overflow interrupt request is disabled */
+	asm volatile("msr pmintenset_el1, %0" : : "r" ((u64)(0 << 31)));
+/*start*/
+	armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMCR_E);
+}
+
+static void
+disable_cpu_counters(void* data)
+{
+	u32 val=0;
+	printk(KERN_INFO "\n [" DRVR_NAME "] disabling user-mode PMU access on CPU #%d",
+	smp_processor_id());
+
+	/* Program PMU and disable all counters */
+	armv8pmu_pmcr_write(armv8pmu_pmcr_read() |~ARMV8_PMCR_E);
+	/* disable user-mode access to counters. */
+	asm volatile("msr pmuserenr_el0, %0" : : "r"((u64)0));
+
+}
+
+static int __init
+init(void)
+{
+	on_each_cpu(enable_cpu_counters, NULL, 1);
+	printk(KERN_INFO "[" DRVR_NAME "] initialized");
+	return 0;
+}
+
+static void __exit
+fini(void)
+{
+	on_each_cpu(disable_cpu_counters, NULL, 1);
+	printk(KERN_INFO "[" DRVR_NAME "] unloaded");
+}
+
+MODULE_AUTHOR("Yogesh Tillu ");
+MODULE_DESCRIPTION("Enables user-mode access to ARMv8 PMU counters");
+MODULE_VERSION("0:0.1-dev");
+module_init(init);
+module_exit(fini);
-- 
1.7.9.5