[PATCH v2] powerpc/papr_scm: Make 'perf_stats' invisible if perf-stats unavailable

[Dan Williams]

On Fri, May 7, 2021 at 4:40 AM Vaibhav Jain <vaibhav at linux.ibm.com> wrote:
>
> In case performance stats for an nvdimm are not available, reading the
> 'perf_stats' sysfs file returns an -ENOENT error. A better approach is
> to make the 'perf_stats' file entirely invisible to indicate that
> performance stats for an nvdimm are unavailable.
>
> So this patch updates 'papr_nd_attribute_group' to add a 'is_visible'
> callback implemented as newly introduced 'papr_nd_attribute_visible()'
> that returns an appropriate mode in case performance stats aren't
> supported in a given nvdimm.
>
> Also the initialization of 'papr_scm_priv.stat_buffer_len' is moved
> from papr_scm_nvdimm_init() to papr_scm_probe() so that it value is
> available when 'papr_nd_attribute_visible()' is called during nvdimm
> initialization.
>
> Fixes: 2d02bf835e57('powerpc/papr_scm: Fetch nvdimm performance stats from PHYP')

Since this has been the exposed ABI since v5.9 perhaps a note /
analysis is needed here that the disappearance of this file will not
break any existing scripts/tools.

> Signed-off-by: Vaibhav Jain <vaibhav at linux.ibm.com>
> ---
> Changelog:
>
> v2:
> * Removed a redundant dev_info() from pap_scm_nvdimm_init() [ Aneesh ]
> * Marked papr_nd_attribute_visible() as static which also fixed the
>   build warning reported by kernel build robot
> ---
>  arch/powerpc/platforms/pseries/papr_scm.c | 35 ++++++++++++++++-------
>  1 file changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index e2b69cc3beaf..11e7b90a3360 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -907,6 +907,20 @@ static ssize_t flags_show(struct device *dev,
>  }
>  DEVICE_ATTR_RO(flags);
>
> +static umode_t papr_nd_attribute_visible(struct kobject *kobj,
> +                                        struct attribute *attr, int n)
> +{
> +       struct device *dev = container_of(kobj, typeof(*dev), kobj);

This can use the kobj_to_dev() helper.

> +       struct nvdimm *nvdimm = to_nvdimm(dev);
> +       struct papr_scm_priv *p = nvdimm_provider_data(nvdimm);
> +
> +       /* For if perf-stats not available remove perf_stats sysfs */
> +       if (attr == &dev_attr_perf_stats.attr && p->stat_buffer_len == 0)
> +               return 0;
> +
> +       return attr->mode;
> +}
> +
>  /* papr_scm specific dimm attributes */
>  static struct attribute *papr_nd_attributes[] = {
>         &dev_attr_flags.attr,
> @@ -916,6 +930,7 @@ static struct attribute *papr_nd_attributes[] = {
>
>  static struct attribute_group papr_nd_attribute_group = {
>         .name = "papr",
> +       .is_visible = papr_nd_attribute_visible,
>         .attrs = papr_nd_attributes,
>  };
>
> @@ -931,7 +946,6 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>         struct nd_region_desc ndr_desc;
>         unsigned long dimm_flags;
>         int target_nid, online_nid;
> -       ssize_t stat_size;
>
>         p->bus_desc.ndctl = papr_scm_ndctl;
>         p->bus_desc.module = THIS_MODULE;
> @@ -1016,16 +1030,6 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>         list_add_tail(&p->region_list, &papr_nd_regions);
>         mutex_unlock(&papr_ndr_lock);
>
> -       /* Try retriving the stat buffer and see if its supported */
> -       stat_size = drc_pmem_query_stats(p, NULL, 0);
> -       if (stat_size > 0) {
> -               p->stat_buffer_len = stat_size;
> -               dev_dbg(&p->pdev->dev, "Max perf-stat size %lu-bytes\n",
> -                       p->stat_buffer_len);
> -       } else {
> -               dev_info(&p->pdev->dev, "Dimm performance stats unavailable\n");
> -       }
> -
>         return 0;
>
>  err:   nvdimm_bus_unregister(p->bus);
> @@ -1102,6 +1106,7 @@ static int papr_scm_probe(struct platform_device *pdev)
>         u64 blocks, block_size;
>         struct papr_scm_priv *p;
>         const char *uuid_str;
> +       ssize_t stat_size;
>         u64 uuid[2];
>         int rc;
>
> @@ -1179,6 +1184,14 @@ static int papr_scm_probe(struct platform_device *pdev)
>         p->res.name  = pdev->name;
>         p->res.flags = IORESOURCE_MEM;
>
> +       /* Try retriving the stat buffer and see if its supported */

s/retriving/retrieving/

> +       stat_size = drc_pmem_query_stats(p, NULL, 0);
> +       if (stat_size > 0) {
> +               p->stat_buffer_len = stat_size;
> +               dev_dbg(&p->pdev->dev, "Max perf-stat size %lu-bytes\n",
> +                       p->stat_buffer_len);
> +       }
> +
>         rc = papr_scm_nvdimm_init(p);
>         if (rc)
>                 goto err2;
> --
> 2.31.1
>

After the minor fixups above you can add:

Reviewed-by: Dan Williams <dan.j.williams at intel.com>

...I assume this will go through the PPC tree.