[RFC PATCH 2/4] powerpc/papr_scm: Add support for PAPR_SCM_PDSM_FETCH_PERF_STATS

[Vaibhav Jain]

Add support for pdsm PAPR_SCM_PDSM_FETCH_PERF_STATS that issues HCALL
H_SCM_PERFORMANCE_STATS to PHYP to fetch all the NVDIMM performance
stats and store them in per nvdimm 'struct papr_scm_priv' as member
'perf_stats'. A further PDSM request (introduced later) is needed to
read the contents of this performance stats buffer.

A new uapi struct 'nd_psdm_perf_stats_size' is introduced to be used
by libndctl to retrieve the size of buffer needed to store all NVDIMM
performance stats.

The patch updates papr_scm_service_pdsm() to route
PAPR_SCM_PDSM_FETCH_PERF_STATS to newly introduced
papr_scm_fetch_perf_stats() which then issues the HCALL and copies the
needed size to the PDSM payload.

Signed-off-by: Vaibhav Jain <vaibhav at linux.ibm.com>
---
 arch/powerpc/include/uapi/asm/papr_scm_pdsm.h | 13 ++++
 arch/powerpc/platforms/pseries/papr_scm.c     | 70 +++++++++++++++++++
 2 files changed, 83 insertions(+)

diff --git a/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h b/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
index db0cf550dabe..40ec55d06f4c 100644
--- a/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
+++ b/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
@@ -114,6 +114,7 @@ struct nd_pdsm_cmd_pkg {
 enum papr_scm_pdsm {
 	PAPR_SCM_PDSM_MIN = 0x0,
 	PAPR_SCM_PDSM_HEALTH,
+	PAPR_SCM_PDSM_FETCH_PERF_STATS,
 	PAPR_SCM_PDSM_MAX,
 };
 
@@ -170,4 +171,16 @@ struct nd_papr_pdsm_health_v1 {
 /* Current version number for the dimm health struct */
 #define ND_PAPR_PDSM_HEALTH_VERSION 1
 
+/*
+ * Return the maximum buffer size needed to hold all performance state.
+ * max_stats_size: The buffer size needed to hold all stat entries
+ */
+struct nd_pdsm_fetch_perf_stats_v1 {
+	__u32 max_stats_size;
+	__u8 reserved[4];
+} __packed;
+
+#define nd_pdsm_fetch_perf_stats nd_pdsm_fetch_perf_stats_v1
+#define ND_PDSM_FETCH_PERF_STATS_VERSION 1
+
 #endif /* _UAPI_ASM_POWERPC_PAPR_SCM_PDSM_H_ */
diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
index fd9a12275315..f8b37a830aed 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c
@@ -525,6 +525,73 @@ static int is_cmd_valid(struct nvdimm *nvdimm, unsigned int cmd, void *buf,
 	return 0;
 }
 
+/* Return the size in bytes for returning all perf stats to libndctl */
+static int papr_scm_fetch_perf_stats(struct papr_scm_priv *p,
+				     struct nd_pdsm_cmd_pkg *pkg)
+{
+	int rc = 0;
+	size_t copysize = sizeof(struct nd_pdsm_fetch_perf_stats);
+	struct nd_pdsm_fetch_perf_stats *sz =
+		(struct nd_pdsm_fetch_perf_stats *)pdsm_cmd_to_payload(pkg);
+
+	/*
+	 * If the requested payload version is greater than one we know
+	 * about, return the payload version we know about and let
+	 * caller/userspace handle.
+	 */
+	if (pkg->payload_version > ND_PDSM_FETCH_PERF_STATS_VERSION)
+		pkg->payload_version = ND_PDSM_FETCH_PERF_STATS_VERSION;
+
+	if (pkg->hdr.nd_size_out < copysize) {
+		dev_dbg(&p->pdev->dev, "Truncated payload (%u). Expected (%lu)",
+			pkg->hdr.nd_size_out, copysize);
+		rc = -ENOSPC;
+		goto out;
+	}
+
+	rc = mutex_lock_interruptible(&p->health_mutex);
+	if (rc)
+		goto out;
+
+	if (!p->len_stat_buffer) {
+		rc = -ENOENT;
+		goto out_unlock;
+	}
+
+	/* Setup the buffer and request phyp for all dimm perf stats data */
+	rc = drc_pmem_query_stats(p, p->perf_stats, p->len_stat_buffer, 0,
+				  NULL);
+	if (rc)
+		goto out_unlock;
+
+	dev_dbg(&p->pdev->dev, "Copying payload size=%lu version=0x%x\n",
+		copysize, pkg->payload_version);
+
+	/*
+	 * Put the buffer size needed in the payload buffer subtracting the
+	 * perf_stat header size.
+	 */
+	if (p->len_stat_buffer > sizeof(struct papr_scm_perf_stats))
+		sz->max_stats_size = p->len_stat_buffer -
+			sizeof(struct papr_scm_perf_stats);
+	else
+		sz->max_stats_size = 0;
+
+	pkg->hdr.nd_fw_size = copysize;
+
+out_unlock:
+	mutex_unlock(&p->health_mutex);
+out:
+	/*
+	 * Put the error in out package and return success from function
+	 * so that errors if any are propogated back to userspace.
+	 */
+	pkg->cmd_status = rc;
+	dev_dbg(&p->pdev->dev, "completion code = %d\n", rc);
+
+	return 0;
+}
+
 /* Fetch the DIMM health info and populate it in provided package. */
 static int papr_scm_get_health(struct papr_scm_priv *p,
 			       struct nd_pdsm_cmd_pkg *pkg)
@@ -594,6 +661,9 @@ static int papr_scm_service_pdsm(struct papr_scm_priv *p,
 	case PAPR_SCM_PDSM_HEALTH:
 		return papr_scm_get_health(p, call_pkg);
 
+	case PAPR_SCM_PDSM_FETCH_PERF_STATS:
+		return papr_scm_fetch_perf_stats(p, call_pkg);
+
 	default:
 		dev_dbg(&p->pdev->dev, "Unsupported PDSM request 0x%llx\n",
 			call_pkg->hdr.nd_command);
-- 
2.26.2