Re: [PATCH RFC 1/4] driver/perf: Add identifier sysfs file for CMN

[John Garry]

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@xxxxxxxxxxxxxxxxx>
> ---
>   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.

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

> +	}
> +	else if (cmn->model == CMN650) {
> +		return sysfs_emit(buf, "%s\n", "CMN650");

I'd use lowercase names

> +	}
> +	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?

> +}
> +
> +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

> +};
> +
> +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
>   };
>