perf tools arm64: Add support for get_cpuid_str function.

The get_cpuid_str function returns the MIDR string of the first online
cpu from the range of cpus associated with the PMU CORE device.
Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ganapatrao Kulkarni <gklkml16@gmail.com>
Cc: Jayachandran C <jnair@caviumnetworks.com>
Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <robert.richter@cavium.com>
Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20171016183222.25750-3-ganapatrao.kulkarni@cavium.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/arm64/util/Build

+libperf-y += header.o
 libperf-$(CONFIG_DWARF)     += dwarf-regs.o
 libperf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
 

tools/perf/arch/arm64/util/header.c

+#include <stdio.h>
+#include <stdlib.h>
+#include <api/fs/fs.h>
+#include "header.h"
+
+#define MIDR "/regs/identification/midr_el1"
+#define MIDR_SIZE 19
+#define MIDR_REVISION_MASK      0xf
+#define MIDR_VARIANT_SHIFT      20
+#define MIDR_VARIANT_MASK       (0xf << MIDR_VARIANT_SHIFT)
+
+char *get_cpuid_str(struct perf_pmu *pmu)
+{
+	char *buf = NULL;
+	char path[PATH_MAX];
+	const char *sysfs = sysfs__mountpoint();
+	int cpu;
+	u64 midr = 0;
+	struct cpu_map *cpus;
+	FILE *file;
+
+	if (!sysfs || !pmu || !pmu->cpus)
+		return NULL;
+
+	buf = malloc(MIDR_SIZE);
+	if (!buf)
+		return NULL;
+
+	/* read midr from list of cpus mapped to this pmu */
+	cpus = cpu_map__get(pmu->cpus);
+	for (cpu = 0; cpu < cpus->nr; cpu++) {
+		scnprintf(path, PATH_MAX, "%s/devices/system/cpu/cpu%d"MIDR,
+				sysfs, cpus->map[cpu]);
+
+		file = fopen(path, "r");
+		if (!file) {
+			pr_debug("fopen failed for file %s\n", path);
+			continue;
+		}
+
+		if (!fgets(buf, MIDR_SIZE, file)) {
+			fclose(file);
+			continue;
+		}
+		fclose(file);
+
+		/* Ignore/clear Variant[23:20] and
+		 * Revision[3:0] of MIDR
+		 */
+		midr = strtoul(buf, NULL, 16);
+		midr &= (~(MIDR_VARIANT_MASK | MIDR_REVISION_MASK));
+		scnprintf(buf, MIDR_SIZE, "0x%016lx", midr);
+		/* got midr break loop */
+		break;
+	}
+
+	if (!midr) {
+		pr_err("failed to get cpuid string for PMU %s\n", pmu->name);
+		free(buf);
+		buf = NULL;
+	}
+
+	cpu_map__put(cpus);
+	return buf;
+}