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Date:   Wed, 29 Mar 2023 19:53:56 +0800
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Subject: Re: [PATCH RFC 1/4] driver/perf: Add identifier sysfs file for CMN
To:     John Garry <john.g.garry@oracle.com>,
        Ian Rogers <irogers@google.com>, Will Deacon <will@kernel.org>,
        James Clark <james.clark@arm.com>,
        Mike Leach <mike.leach@linaro.org>,
        Leo Yan <leo.yan@linaro.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Ilkka Koskinen <ilkka@os.amperecomputing.com>,
        Robin Murphy <robin.murphy@arm.com>
Cc:     linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-perf-users@vger.kernel.org,
        Shuai Xue <xueshuai@linux.alibaba.com>,
        Zhuo Song <zhuo.song@linux.alibaba.com>
References: <1679885172-95021-1-git-send-email-renyu.zj@linux.alibaba.com>
 <1679885172-95021-2-git-send-email-renyu.zj@linux.alibaba.com>
 <72246c5e-6ba5-098b-a979-e90738cc7509@oracle.com>
From:   Jing Zhang <renyu.zj@linux.alibaba.com>
In-Reply-To: <72246c5e-6ba5-098b-a979-e90738cc7509@oracle.com>
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在 2023/3/27 下午3:55, John Garry 写道:
> On 27/03/2023 03:46, Jing Zhang wrote:
>> To allow userspace to identify the specific implementation of the device,
>> add an "identifier" sysfs file.
>>
>> The perf tool can match the arm CMN metric through the identifier.
>>
>> Signed-off-by: Jing Zhang <renyu.zj@linux.alibaba.com>
>> ---
>>   drivers/perf/arm-cmn.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 43 insertions(+)
>>
>> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
>> index c968986..0c138ad 100644
>> --- a/drivers/perf/arm-cmn.c
>> +++ b/drivers/perf/arm-cmn.c
>> @@ -1168,10 +1168,53 @@ static ssize_t arm_cmn_cpumask_show(struct device *dev,
>>       .attrs = arm_cmn_cpumask_attrs,
>>   };
>>   +static ssize_t arm_cmn_identifier_show(struct device *dev,
>> +        struct device_attribute *attr, char *buf)
>> +{
>> +    struct arm_cmn *cmn = to_cmn(dev_get_drvdata(dev));
>> +    if (cmn->model == CMN700) {
>> +        return sysfs_emit(buf, "%s\n", "CMN700");
> 
> Is it possible to have a pointer to this string in struct arm_cmn, such that we don't have to do this model to identifier lookup here? If-else chains like this are not scalable.
> 
Will do.

> BTW, does this HW have some HW identifier register, like iidr? I think that using that may be preferable.
> 

I didn't find the relevant identifier register.

Do Illka and Robin know that there is such a register that can identify different CMN versions? Looking forward to your suggestions.


>> +    }
>> +    else if (cmn->model == CMN650) {
>> +        return sysfs_emit(buf, "%s\n", "CMN650");
> 
> I'd use lowercase names
> 
Ok.

>> +    }
>> +    else if (cmn->model == CMN600) {
>> +        return sysfs_emit(buf, "%s\n", "CMN600");
>> +    }
>> +    else if (cmn->model == CI700) {
>> +        return sysfs_emit(buf, "%s\n", "CI700");
>> +    }
>> +    return sysfs_emit(buf, "%s\n", "UNKNOWN");
> 
> can we have a "is_visble" attr to just no show this when unknown?
> 

Ok.

>> +}
>> +
>> +static umode_t arm_cmn_identifier_attr_visible(struct kobject *kobj,
>> +        struct attribute *attr, int n)
>> +{
>> +    struct device *dev = kobj_to_dev(kobj);
>> +    struct arm_cmn *cmn = to_cmn(dev_get_drvdata(dev));
>> +    if (cmn->model <= 0)
>> +        return 0;
>> +    return attr->mode;
>> +};
>> +
>> +static struct device_attribute arm_cmn_identifier_attr =
>> +__ATTR(identifier, 0444, arm_cmn_identifier_show, NULL);
>> +
>> +static struct attribute *arm_cmn_identifier_attrs[] = {
>> +    &arm_cmn_identifier_attr.attr,
>> +    NULL,
> 
> nit: no need for trailing ',' on a sentinel
> 

Ok, Will do.

>> +};
>> +
>> +static struct attribute_group arm_cmn_identifier_attr_group = {
>> +    .attrs = arm_cmn_identifier_attrs,
>> +    .is_visible = arm_cmn_identifier_attr_visible,
>> +};
>> +
>>   static const struct attribute_group *arm_cmn_attr_groups[] = {
>>       &arm_cmn_event_attrs_group,
>>       &arm_cmn_format_attrs_group,
>>       &arm_cmn_cpumask_attr_group,
>> +    &arm_cmn_identifier_attr_group,
>>       NULL
>>   };
>>