We add support for reporting 'fuel-gauge' NVDIMM metric via
PAPR_PDSM_HEALTH pdsm payload. 'fuel-gauge' metric indicates the usage
life remaining of a papr-scm compatible NVDIMM. PHYP exposes this
metric via the H_SCM_PERFORMANCE_STATS.

The metric value is returned from the pdsm by extending the return
payload 'struct nd_papr_pdsm_health' without breaking the ABI. A new
field 'dimm_fuel_gauge' to hold the metric value is introduced at the
end of the payload struct and its presence is indicated by by
extension flag PDSM_DIMM_HEALTH_RUN_GAUGE_VALID.

The patch introduces a new function papr_pdsm_fuel_gauge() that is
called from papr_pdsm_health(). If fetching NVDIMM performance stats
is supported then 'papr_pdsm_fuel_gauge()' allocated an output buffer
large enough to hold the performance stat and passes it to
drc_pmem_query_stats() that issues the HCALL to PHYP. The return value
of the stat is then populated in the 'struct
nd_papr_pdsm_health.dimm_fuel_gauge' field with extension flag
'PDSM_DIMM_HEALTH_RUN_GAUGE_VALID' set in 'struct
nd_papr_pdsm_health.extension_flags'

Signed-off-by: Vaibhav Jain <vaib...@linux.ibm.com>
---
Changelog:

v3:
* Updated papr_pdsm_fuel_guage() to use the updated
  drc_pmem_query_stats() function.

Resend:
None

v2:
* Restructure code in papr_pdsm_fuel_gauge() to handle error case
first [ Ira ]
* Ignore the return value of papr_pdsm_fuel_gauge() in
papr_psdm_health() [ Ira ]
---
 arch/powerpc/include/uapi/asm/papr_pdsm.h |  9 ++++
 arch/powerpc/platforms/pseries/papr_scm.c | 51 ++++++++++++++++++++++-
 2 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/uapi/asm/papr_pdsm.h 
b/arch/powerpc/include/uapi/asm/papr_pdsm.h
index 9ccecc1d6840..50ef95e2f5b1 100644
--- a/arch/powerpc/include/uapi/asm/papr_pdsm.h
+++ b/arch/powerpc/include/uapi/asm/papr_pdsm.h
@@ -72,6 +72,11 @@
 #define PAPR_PDSM_DIMM_CRITICAL      2
 #define PAPR_PDSM_DIMM_FATAL         3
 
+/* struct nd_papr_pdsm_health.extension_flags field flags */
+
+/* Indicate that the 'dimm_fuel_gauge' field is valid */
+#define PDSM_DIMM_HEALTH_RUN_GAUGE_VALID 1
+
 /*
  * Struct exchanged between kernel & ndctl in for PAPR_PDSM_HEALTH
  * Various flags indicate the health status of the dimm.
@@ -84,6 +89,7 @@
  * dimm_locked         : Contents of the dimm cant be modified until CEC reboot
  * dimm_encrypted      : Contents of dimm are encrypted.
  * dimm_health         : Dimm health indicator. One of PAPR_PDSM_DIMM_XXXX
+ * dimm_fuel_gauge     : Life remaining of DIMM as a percentage from 0-100
  */
 struct nd_papr_pdsm_health {
        union {
@@ -96,6 +102,9 @@ struct nd_papr_pdsm_health {
                        __u8 dimm_locked;
                        __u8 dimm_encrypted;
                        __u16 dimm_health;
+
+                       /* Extension flag PDSM_DIMM_HEALTH_RUN_GAUGE_VALID */
+                       __u16 dimm_fuel_gauge;
                };
                __u8 buf[ND_PDSM_PAYLOAD_MAX_SIZE];
        };
diff --git a/arch/powerpc/platforms/pseries/papr_scm.c 
b/arch/powerpc/platforms/pseries/papr_scm.c
index 29cab86141d8..837a21083268 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c
@@ -518,6 +518,51 @@ static int is_cmd_valid(struct nvdimm *nvdimm, unsigned 
int cmd, void *buf,
        return 0;
 }
 
+static int papr_pdsm_fuel_gauge(struct papr_scm_priv *p,
+                               union nd_pdsm_payload *payload)
+{
+       int rc, size;
+       u64 statval;
+       struct papr_scm_perf_stat *stat;
+       struct papr_scm_perf_stats *stats;
+
+       /* Silently fail if fetching performance metrics isn't  supported */
+       if (!p->stat_buffer_len)
+               return 0;
+
+       /* Allocate request buffer enough to hold single performance stat */
+       size = sizeof(struct papr_scm_perf_stats) +
+               sizeof(struct papr_scm_perf_stat);
+
+       stats = kzalloc(size, GFP_KERNEL);
+       if (!stats)
+               return -ENOMEM;
+
+       stat = &stats->scm_statistic[0];
+       memcpy(&stat->stat_id, "MemLife ", sizeof(stat->stat_id));
+       stat->stat_val = 0;
+
+       /* Fetch the fuel gauge and populate it in payload */
+       rc = drc_pmem_query_stats(p, stats, 1);
+       if (rc < 0) {
+               dev_dbg(&p->pdev->dev, "Err(%d) fetching fuel gauge\n", rc);
+               goto free_stats;
+       }
+
+       statval = be64_to_cpu(stat->stat_val);
+       dev_dbg(&p->pdev->dev,
+               "Fetched fuel-gauge %llu", statval);
+       payload->health.extension_flags |=
+               PDSM_DIMM_HEALTH_RUN_GAUGE_VALID;
+       payload->health.dimm_fuel_gauge = statval;
+
+       rc = sizeof(struct nd_papr_pdsm_health);
+
+free_stats:
+       kfree(stats);
+       return rc;
+}
+
 /* Fetch the DIMM health info and populate it in provided package. */
 static int papr_pdsm_health(struct papr_scm_priv *p,
                            union nd_pdsm_payload *payload)
@@ -558,6 +603,10 @@ static int papr_pdsm_health(struct papr_scm_priv *p,
 
        /* struct populated hence can release the mutex now */
        mutex_unlock(&p->health_mutex);
+
+       /* Populate the fuel gauge meter in the payload */
+       papr_pdsm_fuel_gauge(p, payload);
+
        rc = sizeof(struct nd_papr_pdsm_health);
 
 out:
@@ -752,7 +801,7 @@ static ssize_t perf_stats_show(struct device *dev,
                return -ENOMEM;
 
        /* Ask phyp to return all dimm perf stats */
-       rc = drc_pmem_query_stats(p, stats, p->stat_buffer_len, 0, NULL);
+       rc = drc_pmem_query_stats(p, stats, 0);
        if (rc)
                goto free_stats;
        /*
-- 
2.26.2

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