Date: Thu, 10 Aug 2017 18:15:50 +0100
From: Will Deacon <will.deacon@arm.com>
To: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>
Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        catalin.marinas@arm.com, mark.rutland@arm.com, acme@kernel.org,
        alexander.shishkin@linux.intel.com, peterz@infradead.org,
        mingo@redhat.com, jnair@caviumnetworks.com, zhangshaokun@hisilicon.com,
        Robert.Richter@cavium.com, gpkulkarni@gmail.com
Subject: Re: [PATCH v4 2/4] perf tools arm64: Add support for get_cpuid_str
 function.
Message-ID: <20170810171549.GE8173@arm.com>
References: <20170720055608.5333-1-ganapatrao.kulkarni@cavium.com>
 <20170720055608.5333-3-ganapatrao.kulkarni@cavium.com>
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On Thu, Jul 20, 2017 at 11:26:06AM +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 | 59 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 60 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..4e25498
> --- /dev/null
> +++ b/tools/perf/arch/arm64/util/header.c
> @@ -0,0 +1,59 @@
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <api/fs/fs.h>
> +#include "header.h"
> +
> +#define MIDR "/regs/identification/midr_el1"
> +#define MIDR_SIZE 128
> +
> +char *get_cpuid_str(struct perf_pmu *pmu)
> +{
> +	char *buf = malloc(MIDR_SIZE);
> +	char *temp = NULL;
> +	char path[PATH_MAX];
> +	const char *sysfs = sysfs__mountpoint();
> +	int cpu, ret;
> +	unsigned long long midr;
> +	struct cpu_map *cpus;
> +	FILE *file;
> +
> +	if (!pmu->cpus)
> +		return NULL;
> +
> +	if (!sysfs)
> +		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++) {
> +		ret = snprintf(path, PATH_MAX,
> +				"%s/devices/system/cpu/cpu%d"MIDR,
> +				sysfs, cpus->map[cpu]);
> +		if (ret == PATH_MAX) {
> +			pr_err("sysfs path crossed PATH_MAX(%d) size\n", PATH_MAX);
> +			goto err;
> +		}
> +
> +		file = fopen(path, "r");
> +		if (!file)
> +			continue;
> +
> +		temp = fgets(buf, MIDR_SIZE, file);
> +		fclose(file);
> +		if (!temp)
> +			continue;
> +
> +		/* Ignore/clear Variant[23:20] and
> +		 * Revision[3:0] of MIDR
> +		 */
> +		midr = strtoll(buf, NULL, 16);
> +		midr &= (~(0xf << 20 | 0xf));
> +		snprintf(buf, MIDR_SIZE, "0x%016llx", midr);
> +		cpu_map__put(cpus);
> +		return buf;
> +	}
> +
> +err:	cpu_map__put(cpus);
> +	free(buf);
> +	return NULL;
> +}

Might just be me, but I found this really difficult to read. I think it
works, but having the return at the end of loop is really counter-intuitive.

I'll leave it up to Arnaldo, since I can't find any functional problems
with this series from the arm64 side.

Cheers,

Will