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    SubjectRe: [PATCH v5 2/4] perf tools arm64: Add support for get_cpuid_str function.
    On Wed, Aug 16, 2017 at 12:40:46PM +0530, Ganapatrao Kulkarni wrote:
    > function get_cpuid_str returns 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>
    > ---
    > tools/perf/arch/arm64/util/Build | 1 +
    > tools/perf/arch/arm64/util/header.c | 61 +++++++++++++++++++++++++++++++++++++
    > 2 files changed, 62 insertions(+)
    > create mode 100644 tools/perf/arch/arm64/util/header.c
    >
    > diff --git a/tools/perf/arch/arm64/util/Build b/tools/perf/arch/arm64/util/Build
    > index cef6fb3..b1ab72d 100644
    > --- a/tools/perf/arch/arm64/util/Build
    > +++ b/tools/perf/arch/arm64/util/Build
    > @@ -1,3 +1,4 @@
    > +libperf-y += header.o
    > libperf-$(CONFIG_DWARF) += dwarf-regs.o
    > libperf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
    >
    > diff --git a/tools/perf/arch/arm64/util/header.c b/tools/perf/arch/arm64/util/header.c
    > new file mode 100644
    > index 0000000..713ef17
    > --- /dev/null
    > +++ b/tools/perf/arch/arm64/util/header.c
    > @@ -0,0 +1,61 @@
    > +#include <stdio.h>
    > +#include <stdlib.h>
    > +#include <api/fs/fs.h>
    > +#include "header.h"
    > +
    > +#define MIDR "/regs/identification/midr_el1"
    > +#define MIDR_SIZE 128

    Why is this so big?

    > +char *get_cpuid_str(struct perf_pmu *pmu)
    > +{
    > + char *buf = NULL;
    > + char *temp = NULL;
    > + char path[PATH_MAX];
    > + const char *sysfs = sysfs__mountpoint();
    > + int cpu;
    > + unsigned long long midr = 0;
    > + struct cpu_map *cpus;
    > + FILE *file;
    > +
    > + if (!sysfs || !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_err("fopen failed for file %s\n", path);

    pr_debug instead? It's not fatal if a CPU is hotplugged off and you can't
    read its midr.

    > + continue;
    > + }
    > +
    > + temp = fgets(buf, MIDR_SIZE, file);
    > + if (!temp)
    > + continue;

    Do you actually need a temporary variable for this?

    > + fclose(file);
    > +
    > + /* Ignore/clear Variant[23:20] and
    > + * Revision[3:0] of MIDR
    > + */
    > + midr = strtoll(buf, NULL, 16);
    > + midr &= (~(0xf << 20 | 0xf));

    If midr really needs to be unsigned long long (u64 might be better), then
    you need to fix these immediates to have a ULL suffix.

    Can you use the GENMASK_ULL macro to generate the MIDR mask, or is that
    not available here?

    > + scnprintf(buf, MIDR_SIZE, "0x%016llx", midr);
    > + /* got midr break loop */
    > + break;
    > + }
    > +
    > + if (!midr) {
    > + free(buf);
    > + buf = NULL;

    If you want the pr_err, here would seem more appropriate because at this
    point we've actually failed.

    Will

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