[RFC PATCH 4/4] powerpc/papr_scm: Add support for PDSM GET_PERF_STAT

[Vaibhav Jain <vaibhav@linux.ibm.com>]

This patch adds support for retrieving a singled NVDIMM performance
stat from PHYP via PDSM GET_PERF_STAT_VERSION. A new uapi 'struct
nd_pdsm_get_perf_stat' is introduced that holds a single performance
stat and is populated by newly introduced papr_scm_get_perf_stat() by
issuing an H_SCM_PERFORMANCE_STATS to PHYP.

Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
---
 arch/powerpc/include/uapi/asm/papr_scm_pdsm.h | 12 +++
 arch/powerpc/platforms/pseries/papr_scm.c     | 74 +++++++++++++++++++
 2 files changed, 86 insertions(+)

diff --git a/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h b/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
index 2db4ffdff285..473c4bbddb2f 100644
--- a/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
+++ b/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
@@ -116,6 +116,7 @@ enum papr_scm_pdsm {
 	PAPR_SCM_PDSM_HEALTH,
 	PAPR_SCM_PDSM_FETCH_PERF_STATS,
 	PAPR_SCM_PDSM_READ_PERF_STATS,
+	PAPR_SCM_PDSM_GET_PERF_STAT,
 	PAPR_SCM_PDSM_MAX,
 };
 
@@ -218,4 +219,15 @@ struct nd_pdsm_read_perf_stats_v1 {
 #define nd_pdsm_read_perf_stats nd_pdsm_read_perf_stats_v1
 #define ND_PDSM_READ_PERF_STATS_VERSION 1
 
+/*
+ * Fetch the value of single nvdimm performance stat id of which is
+ * stored in 'stat.id'
+ */
+struct nd_pdsm_get_perf_stat_v1 {
+	struct nd_pdsm_perf_stat stat;
+} __packed;
+
+#define nd_pdsm_get_perf_stat nd_pdsm_get_perf_stat_v1
+#define ND_PDSM_GET_PERF_STAT_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 06744d7fe727..284d04f0a094 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c
@@ -525,6 +525,77 @@ static int is_cmd_valid(struct nvdimm *nvdimm, unsigned int cmd, void *buf,
 	return 0;
 }
 
+static int papr_scm_get_perf_stat(struct papr_scm_priv *p,
+				  struct nd_pdsm_cmd_pkg *pkg)
+{
+	int rc;
+	struct nd_pdsm_get_perf_stat *stat =
+		(struct nd_pdsm_get_perf_stat *)pdsm_cmd_to_payload(pkg);
+	const size_t copysize = sizeof(struct nd_pdsm_get_perf_stat);
+	struct papr_scm_perf_stats *stats_req;
+	ssize_t stat_size;
+
+	/*
+	 * 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_GET_PERF_STAT_VERSION)
+		pkg->payload_version = ND_PDSM_GET_PERF_STAT_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;
+	}
+
+	if (!READ_ONCE(p->len_stat_buffer)) {
+		dev_dbg(&p->pdev->dev, "Perf stat: req for unsupported device");
+		rc = -ENOENT;
+		goto out;
+	}
+
+	/* Allocate and setup a PERFORMANCE_STATS request buffer */
+	stat_size = sizeof(struct papr_scm_perf_stats) +
+		sizeof(struct papr_scm_perf_stat);
+	stats_req = kzalloc(stat_size, GFP_KERNEL);
+	if (!stats_req) {
+		dev_err(&p->pdev->dev, "Perf stat: Unable to allocate memory\n");
+		rc = -ENOMEM;
+		goto out;
+	}
+
+	/* Copy the single request statistic_id into the request buffer */
+	memcpy(&stats_req->scm_statistics[0].statistic_id, &stat->stat.id,
+	       sizeof(stats_req->scm_statistics[0].statistic_id));
+
+	/* Fetch the stat from PHYP */
+	rc = drc_pmem_query_stats(p, stats_req, stat_size, 1, NULL);
+	if (rc)
+		goto out;
+
+	/* Copy the value of stat to the return payload */
+	memcpy(&stat->stat.id, &stats_req->scm_statistics[0].statistic_id,
+	       sizeof(stat->stat.id));
+	stat->stat.val = stats_req->scm_statistics[0].statistic_value;
+
+	pkg->hdr.nd_fw_size = copysize;
+
+	dev_dbg(&p->pdev->dev, "Copying payload size=%u version=0x%x\n",
+		pkg->hdr.nd_fw_size, pkg->payload_version);
+
+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;
+}
+
 /*
  * Read the contents of dimm performance statistics buffer at the given
  * 'in_offset' and copy 'in_length' number of bytes to the pkg payload.
@@ -755,6 +826,9 @@ static int papr_scm_service_pdsm(struct papr_scm_priv *p,
 	case PAPR_SCM_PDSM_READ_PERF_STATS:
 		return papr_scm_read_perf_stats(p, call_pkg);
 
+	case PAPR_SCM_PDSM_GET_PERF_STAT:
+		return papr_scm_get_perf_stat(p, call_pkg);
+
 	default:
 		dev_dbg(&p->pdev->dev, "Unsupported PDSM request 0x%llx\n",
 			call_pkg->hdr.nd_command);
-- 
2.26.2
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