Re: [PATCH v2 1/5] driver/perf: Add identifier sysfs file for CMN

[John Garry <john.g.garry@oracle.com>]

On 24/04/2023 10:44, 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 | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 49 insertions(+)
> 
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index c968986..f425610 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -334,6 +334,7 @@ struct arm_cmn {
>   
>   	struct pmu pmu;
>   	struct dentry *debug;
> +	const char *identifier;
>   };
>   
>   #define to_cmn(p)	container_of(p, struct arm_cmn, pmu)
> @@ -1168,10 +1169,41 @@ 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));
> +
> +	return sysfs_emit(buf, "%s\n", cmn->identifier);
> +}
> +
> +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->identifier == NULL)
> +		return 0;

nit: generally if (!val) is preferred

> +	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
> +};
> +
> +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
>   };
>   
> @@ -2241,6 +2273,22 @@ static int arm_cmn600_of_probe(struct device_node *np)
>   	return of_property_read_u32(np, "arm,root-node", &rootnode) ?: rootnode;
>   }
>   
> +const char *arm_cmn_identifier(unsigned long model)
> +{
> +	switch (model) {
> +	case CMN600:
> +		return "cmn600";
> +	case CMN650:
> +		return "cmn650";
> +	case CMN700:
> +		return "cmn700";
> +	case CI700:
> +		return "ci700";
> +	default:
> +		return NULL;
> +	}

nit: I think that it would be nicer to have this per-model string stored 
statically in arm_cmn_acpi_match[].driver_data and 
arm_cmn_of_match[].data, so we have a straight lookup

> +}
> +
>   static int arm_cmn_probe(struct platform_device *pdev)
>   {
>   	struct arm_cmn *cmn;
> @@ -2254,6 +2302,7 @@ static int arm_cmn_probe(struct platform_device *pdev)
>   
>   	cmn->dev = &pdev->dev;
>   	cmn->model = (unsigned long)device_get_match_data(cmn->dev);
> +	cmn->identifier = arm_cmn_identifier(cmn->model);
>   	platform_set_drvdata(pdev, cmn);
>