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

[Vaibhav Jain]

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')
Signed-off-by: Vaibhav Jain <vaib...@linux.ibm.com>
---
 arch/powerpc/platforms/pseries/papr_scm.c | 37 ++++++++++++++++-------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/papr_scm.c 
b/arch/powerpc/platforms/pseries/papr_scm.c
index 12f1513f0fca..90f0af8fefe8 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);
 
+umode_t papr_nd_attribute_visible(struct kobject *kobj, struct attribute *attr,
+                                 int n)
+{
+       struct device *dev = container_of(kobj, typeof(*dev), kobj);
+       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 +1184,16 @@ 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 */
+       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");
+       }
+
        rc = papr_scm_nvdimm_init(p);
        if (rc)
                goto err2;
-- 
2.31.1
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