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From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Vaibhav Jain <vaibhav@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org,
        linux-nvdimm@lists.01.org
Subject: Re: [PATCH 1/2] powerpc/papr_scm: Fetch nvdimm performance stats
 from PHYP
In-Reply-To: <20200622042451.22448-2-vaibhav@linux.ibm.com>
References: <20200622042451.22448-1-vaibhav@linux.ibm.com>
 <20200622042451.22448-2-vaibhav@linux.ibm.com>
Date: Tue, 23 Jun 2020 11:12:15 +0530
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Vaibhav Jain <vaibhav@linux.ibm.com> writes:

> Update papr_scm.c to query dimm performance statistics from PHYP via
> H_SCM_PERFORMANCE_STATS hcall and export them to user-space as PAPR
> specific NVDIMM attribute 'perf_stats' in sysfs. The patch also
> provide a sysfs ABI documentation for the stats being reported and
> their meanings.
>
> During NVDIMM probe time in papr_scm_nvdimm_init() a special variant
> of H_SCM_PERFORMANCE_STATS hcall is issued to check if collection of
> performance statistics is supported or not. If successful then a PHYP
> returns a maximum possible buffer length needed to read all
> performance stats. This returned value is stored in a per-nvdimm
> attribute 'len_stat_buffer'.
>
> The layout of request buffer for reading NVDIMM performance stats from
> PHYP is defined in 'struct papr_scm_perf_stats' and 'struct
> papr_scm_perf_stat'. These structs are used in newly introduced
> drc_pmem_query_stats() that issues the H_SCM_PERFORMANCE_STATS hcall.
>
> The sysfs access function perf_stats_show() uses value
> 'len_stat_buffer' to allocate a buffer large enough to hold all
> possible NVDIMM performance stats and passes it to
> drc_pmem_query_stats() to populate. Finally statistics reported in the
> buffer are formatted into the sysfs access function output buffer.
>
> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
> ---
>  Documentation/ABI/testing/sysfs-bus-papr-pmem |  27 ++++
>  arch/powerpc/platforms/pseries/papr_scm.c     | 139 ++++++++++++++++++
>  2 files changed, 166 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-papr-pmem b/Documentation/ABI/testing/sysfs-bus-papr-pmem
> index 5b10d036a8d4..c1a67275c43f 100644
> --- a/Documentation/ABI/testing/sysfs-bus-papr-pmem
> +++ b/Documentation/ABI/testing/sysfs-bus-papr-pmem
> @@ -25,3 +25,30 @@ Description:
>  				  NVDIMM have been scrubbed.
>  		* "locked"	: Indicating that NVDIMM contents cant
>  				  be modified until next power cycle.
> +
> +What:		/sys/bus/nd/devices/nmemX/papr/perf_stats
> +Date:		May, 2020
> +KernelVersion:	v5.9
> +Contact:	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, linux-nvdimm@lists.01.org,
> +Description:
> +		(RO) Report various performance stats related to papr-scm NVDIMM
> +		device.  Each stat is reported on a new line with each line
> +		composed of a stat-identifier followed by it value. Below are
> +		currently known dimm performance stats which are reported:
> +
> +		* "CtlResCt" : Controller Reset Count
> +		* "CtlResTm" : Controller Reset Elapsed Time
> +		* "PonSecs " : Power-on Seconds
> +		* "MemLife " : Life Remaining
> +		* "CritRscU" : Critical Resource Utilization
> +		* "HostLCnt" : Host Load Count
> +		* "HostSCnt" : Host Store Count
> +		* "HostSDur" : Host Store Duration
> +		* "HostLDur" : Host Load Duration
> +		* "MedRCnt " : Media Read Count
> +		* "MedWCnt " : Media Write Count
> +		* "MedRDur " : Media Read Duration
> +		* "MedWDur " : Media Write Duration
> +		* "CchRHCnt" : Cache Read Hit Count
> +		* "CchWHCnt" : Cache Write Hit Count
> +		* "FastWCnt" : Fast Write Count
> \ No newline at end of file
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index 9c569078a09f..cb3f9acc325b 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -62,6 +62,24 @@
>  				    PAPR_PMEM_HEALTH_FATAL |	\
>  				    PAPR_PMEM_HEALTH_UNHEALTHY)
>  
> +#define PAPR_SCM_PERF_STATS_EYECATCHER __stringify(SCMSTATS)
> +#define PAPR_SCM_PERF_STATS_VERSION 0x1
> +
> +/* Struct holding a single performance metric */
> +struct papr_scm_perf_stat {
> +	u8 statistic_id[8];
> +	u64 statistic_value;

May be stat_id, stat_val ? 

> +};
> +
> +/* Struct exchanged between kernel and PHYP for fetching drc perf stats */
> +struct papr_scm_perf_stats {
> +	u8 eye_catcher[8];
> +	u32 stats_version;		/* Should be 0x01 */
> +	u32 num_statistics;		/* Number of stats following */
> +	/* zero or more performance matrics */
> +	struct papr_scm_perf_stat scm_statistic[];
> +} __packed;


For Phyp interaction these should be big-endian. I see you do 

	stats[i].statistic_value = be64_to_cpu(stats[i].statistic_value);

Can we avoid that?


> +
>  /* private struct associated with each region */
>  struct papr_scm_priv {
>  	struct platform_device *pdev;
> @@ -89,6 +107,9 @@ struct papr_scm_priv {
>  
>  	/* Health information for the dimm */
>  	u64 health_bitmap;
> +
> +	/* length of the stat buffer as expected by phyp */
> +	size_t len_stat_buffer;

how about stat_buffer_len?

>  };
>  
>  static int drc_pmem_bind(struct papr_scm_priv *p)
> @@ -194,6 +215,75 @@ static int drc_pmem_query_n_bind(struct papr_scm_priv *p)
>  	return drc_pmem_bind(p);
>  }
>  
> +/*
> + * Query the Dimm performance stats from PHYP and copy them (if returned) to
> + * provided struct papr_scm_perf_stats instance 'stats' of 'size' in bytes.
> + * The value of R4 is copied to 'out' if the pointer is provided.
> + */
> +static int drc_pmem_query_stats(struct papr_scm_priv *p,
> +				struct papr_scm_perf_stats *buff_stats,
> +				size_t size, unsigned int num_stats,
> +				uint64_t *out)
> +{
> +	unsigned long ret[PLPAR_HCALL_BUFSIZE];
> +	struct papr_scm_perf_stat *stats;
> +	s64 rc, i;
> +
> +	/* Setup the out buffer */
> +	if (buff_stats) {
> +		memcpy(buff_stats->eye_catcher,
> +		       PAPR_SCM_PERF_STATS_EYECATCHER, 8);
> +		buff_stats->stats_version =
> +			cpu_to_be32(PAPR_SCM_PERF_STATS_VERSION);
> +		buff_stats->num_statistics =
> +			cpu_to_be32(num_stats);
> +	} else {
> +		/* In case of no out buffer ignore the size */
> +		size = 0;
> +	}
> +
> +	/*
> +	 * Do the HCALL asking PHYP for info and if R4 was requested
> +	 * return its value in 'out' variable.
> +	 */
> +	rc = plpar_hcall(H_SCM_PERFORMANCE_STATS, ret, p->drc_index,
> +			 virt_to_phys(buff_stats), size);
> +	if (out)
> +		*out =  ret[0];
> +
> +	if (rc == H_PARTIAL) {
> +		dev_err(&p->pdev->dev,
> +			"Unknown performance stats, Err:0x%016lX\n", ret[0]);
> +		return -ENOENT;
> +	} else if (rc != H_SUCCESS) {
> +		dev_err(&p->pdev->dev,
> +			"Failed to query performance stats, Err:%lld\n", rc);
> +		return -ENXIO;

May be just -1? ENXIO is that a suitable error return here?

> +	}
> +
> +	/* Successfully fetched the requested stats from phyp */
> +	if (size != 0) {
> +		buff_stats->num_statistics =
> +			be32_to_cpu(buff_stats->num_statistics);
> +
> +		/* Transform the stats buffer values from BE to cpu native */
> +		for (i = 0, stats = buff_stats->scm_statistic;
> +		     i < buff_stats->num_statistics; ++i) {
> +			stats[i].statistic_value =
> +				be64_to_cpu(stats[i].statistic_value);
> +		}
> +		dev_dbg(&p->pdev->dev,
> +			"Performance stats returned %d stats\n",
> +			buff_stats->num_statistics);
> +	} else {
> +		/* Handle case where stat buffer size was requested */
> +		dev_dbg(&p->pdev->dev,
> +			"Performance stats size %ld\n", ret[0]);
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * Issue hcall to retrieve dimm health info and populate papr_scm_priv with the
>   * health information.
> @@ -631,6 +721,45 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
>  	return 0;
>  }
>  
> +static ssize_t perf_stats_show(struct device *dev,
> +			       struct device_attribute *attr, char *buf)
> +{
> +	int index, rc;
> +	struct seq_buf s;
> +	struct papr_scm_perf_stat *stat;
> +	struct papr_scm_perf_stats *stats;
> +	struct nvdimm *dimm = to_nvdimm(dev);
> +	struct papr_scm_priv *p = nvdimm_provider_data(dimm);
> +
> +	if (!p->len_stat_buffer)
> +		return -ENOENT;
> +
> +	/* Allocate the buffer for phyp where stats are written */
> +	stats = kzalloc(p->len_stat_buffer, GFP_KERNEL);
> +	if (!stats)
> +		return -ENOMEM;
> +
> +	/* Ask phyp to return all dimm perf stats */
> +	rc = drc_pmem_query_stats(p, stats, p->len_stat_buffer, 0, NULL);
> +	if (!rc) {
> +		/*
> +		 * Go through the returned output buffer and print stats and
> +		 * values. Since statistic_id is essentially a char string of
> +		 * 8 bytes, simply use the string format specifier to print it.
> +		 */
> +		seq_buf_init(&s, buf, PAGE_SIZE);
> +		for (index = 0, stat = stats->scm_statistic;
> +		     index < stats->num_statistics; ++index, ++stat) {
> +			seq_buf_printf(&s, "%.8s = 0x%016llX\n",
> +				       stat->statistic_id, stat->statistic_value);


That is raw number (statistic_id). Is that useful? Can we map them to user readable
strings? 

> +		}
> +	}
> +
> +	kfree(stats);
> +	return rc ? rc : seq_buf_used(&s);
> +}
> +DEVICE_ATTR_RO(perf_stats);
> +
>  static ssize_t flags_show(struct device *dev,
>  			  struct device_attribute *attr, char *buf)
>  {
> @@ -676,6 +805,7 @@ DEVICE_ATTR_RO(flags);
>  /* papr_scm specific dimm attributes */
>  static struct attribute *papr_nd_attributes[] = {
>  	&dev_attr_flags.attr,
> +	&dev_attr_perf_stats.attr,
>  	NULL,
>  };
>  
> @@ -696,6 +826,7 @@ 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;
> +	u64 stat_size;
>  
>  	p->bus_desc.ndctl = papr_scm_ndctl;
>  	p->bus_desc.module = THIS_MODULE;
> @@ -759,6 +890,14 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>  		dev_info(dev, "Region registered with target node %d and online node %d",
>  			 target_nid, online_nid);
>  
> +	/* Try retriving the stat buffer and see if its supported */
> +	if (!drc_pmem_query_stats(p, NULL, 0, 0, &stat_size)) {
> +		p->len_stat_buffer = (size_t)stat_size;
> +		dev_dbg(&p->pdev->dev, "Max perf-stat size %lu-bytes\n",
> +			p->len_stat_buffer);
> +	} else {
> +		dev_info(&p->pdev->dev, "Limited dimm stat info available\n");
> +	}
>  	return 0;
>  
>  err:	nvdimm_bus_unregister(p->bus);
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From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Vaibhav Jain <vaibhav@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org,
 linux-nvdimm@lists.01.org
Subject: Re: [PATCH 1/2] powerpc/papr_scm: Fetch nvdimm performance stats
 from PHYP
In-Reply-To: <20200622042451.22448-2-vaibhav@linux.ibm.com>
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 <20200622042451.22448-2-vaibhav@linux.ibm.com>
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Vaibhav Jain <vaibhav@linux.ibm.com> writes:

> Update papr_scm.c to query dimm performance statistics from PHYP via
> H_SCM_PERFORMANCE_STATS hcall and export them to user-space as PAPR
> specific NVDIMM attribute 'perf_stats' in sysfs. The patch also
> provide a sysfs ABI documentation for the stats being reported and
> their meanings.
>
> During NVDIMM probe time in papr_scm_nvdimm_init() a special variant
> of H_SCM_PERFORMANCE_STATS hcall is issued to check if collection of
> performance statistics is supported or not. If successful then a PHYP
> returns a maximum possible buffer length needed to read all
> performance stats. This returned value is stored in a per-nvdimm
> attribute 'len_stat_buffer'.
>
> The layout of request buffer for reading NVDIMM performance stats from
> PHYP is defined in 'struct papr_scm_perf_stats' and 'struct
> papr_scm_perf_stat'. These structs are used in newly introduced
> drc_pmem_query_stats() that issues the H_SCM_PERFORMANCE_STATS hcall.
>
> The sysfs access function perf_stats_show() uses value
> 'len_stat_buffer' to allocate a buffer large enough to hold all
> possible NVDIMM performance stats and passes it to
> drc_pmem_query_stats() to populate. Finally statistics reported in the
> buffer are formatted into the sysfs access function output buffer.
>
> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
> ---
>  Documentation/ABI/testing/sysfs-bus-papr-pmem |  27 ++++
>  arch/powerpc/platforms/pseries/papr_scm.c     | 139 ++++++++++++++++++
>  2 files changed, 166 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-papr-pmem b/Documentation/ABI/testing/sysfs-bus-papr-pmem
> index 5b10d036a8d4..c1a67275c43f 100644
> --- a/Documentation/ABI/testing/sysfs-bus-papr-pmem
> +++ b/Documentation/ABI/testing/sysfs-bus-papr-pmem
> @@ -25,3 +25,30 @@ Description:
>  				  NVDIMM have been scrubbed.
>  		* "locked"	: Indicating that NVDIMM contents cant
>  				  be modified until next power cycle.
> +
> +What:		/sys/bus/nd/devices/nmemX/papr/perf_stats
> +Date:		May, 2020
> +KernelVersion:	v5.9
> +Contact:	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, linux-nvdimm@lists.01.org,
> +Description:
> +		(RO) Report various performance stats related to papr-scm NVDIMM
> +		device.  Each stat is reported on a new line with each line
> +		composed of a stat-identifier followed by it value. Below are
> +		currently known dimm performance stats which are reported:
> +
> +		* "CtlResCt" : Controller Reset Count
> +		* "CtlResTm" : Controller Reset Elapsed Time
> +		* "PonSecs " : Power-on Seconds
> +		* "MemLife " : Life Remaining
> +		* "CritRscU" : Critical Resource Utilization
> +		* "HostLCnt" : Host Load Count
> +		* "HostSCnt" : Host Store Count
> +		* "HostSDur" : Host Store Duration
> +		* "HostLDur" : Host Load Duration
> +		* "MedRCnt " : Media Read Count
> +		* "MedWCnt " : Media Write Count
> +		* "MedRDur " : Media Read Duration
> +		* "MedWDur " : Media Write Duration
> +		* "CchRHCnt" : Cache Read Hit Count
> +		* "CchWHCnt" : Cache Write Hit Count
> +		* "FastWCnt" : Fast Write Count
> \ No newline at end of file
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index 9c569078a09f..cb3f9acc325b 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -62,6 +62,24 @@
>  				    PAPR_PMEM_HEALTH_FATAL |	\
>  				    PAPR_PMEM_HEALTH_UNHEALTHY)
>  
> +#define PAPR_SCM_PERF_STATS_EYECATCHER __stringify(SCMSTATS)
> +#define PAPR_SCM_PERF_STATS_VERSION 0x1
> +
> +/* Struct holding a single performance metric */
> +struct papr_scm_perf_stat {
> +	u8 statistic_id[8];
> +	u64 statistic_value;

May be stat_id, stat_val ? 

> +};
> +
> +/* Struct exchanged between kernel and PHYP for fetching drc perf stats */
> +struct papr_scm_perf_stats {
> +	u8 eye_catcher[8];
> +	u32 stats_version;		/* Should be 0x01 */
> +	u32 num_statistics;		/* Number of stats following */
> +	/* zero or more performance matrics */
> +	struct papr_scm_perf_stat scm_statistic[];
> +} __packed;


For Phyp interaction these should be big-endian. I see you do 

	stats[i].statistic_value = be64_to_cpu(stats[i].statistic_value);

Can we avoid that?


> +
>  /* private struct associated with each region */
>  struct papr_scm_priv {
>  	struct platform_device *pdev;
> @@ -89,6 +107,9 @@ struct papr_scm_priv {
>  
>  	/* Health information for the dimm */
>  	u64 health_bitmap;
> +
> +	/* length of the stat buffer as expected by phyp */
> +	size_t len_stat_buffer;

how about stat_buffer_len?

>  };
>  
>  static int drc_pmem_bind(struct papr_scm_priv *p)
> @@ -194,6 +215,75 @@ static int drc_pmem_query_n_bind(struct papr_scm_priv *p)
>  	return drc_pmem_bind(p);
>  }
>  
> +/*
> + * Query the Dimm performance stats from PHYP and copy them (if returned) to
> + * provided struct papr_scm_perf_stats instance 'stats' of 'size' in bytes.
> + * The value of R4 is copied to 'out' if the pointer is provided.
> + */
> +static int drc_pmem_query_stats(struct papr_scm_priv *p,
> +				struct papr_scm_perf_stats *buff_stats,
> +				size_t size, unsigned int num_stats,
> +				uint64_t *out)
> +{
> +	unsigned long ret[PLPAR_HCALL_BUFSIZE];
> +	struct papr_scm_perf_stat *stats;
> +	s64 rc, i;
> +
> +	/* Setup the out buffer */
> +	if (buff_stats) {
> +		memcpy(buff_stats->eye_catcher,
> +		       PAPR_SCM_PERF_STATS_EYECATCHER, 8);
> +		buff_stats->stats_version =
> +			cpu_to_be32(PAPR_SCM_PERF_STATS_VERSION);
> +		buff_stats->num_statistics =
> +			cpu_to_be32(num_stats);
> +	} else {
> +		/* In case of no out buffer ignore the size */
> +		size = 0;
> +	}
> +
> +	/*
> +	 * Do the HCALL asking PHYP for info and if R4 was requested
> +	 * return its value in 'out' variable.
> +	 */
> +	rc = plpar_hcall(H_SCM_PERFORMANCE_STATS, ret, p->drc_index,
> +			 virt_to_phys(buff_stats), size);
> +	if (out)
> +		*out =  ret[0];
> +
> +	if (rc == H_PARTIAL) {
> +		dev_err(&p->pdev->dev,
> +			"Unknown performance stats, Err:0x%016lX\n", ret[0]);
> +		return -ENOENT;
> +	} else if (rc != H_SUCCESS) {
> +		dev_err(&p->pdev->dev,
> +			"Failed to query performance stats, Err:%lld\n", rc);
> +		return -ENXIO;

May be just -1? ENXIO is that a suitable error return here?

> +	}
> +
> +	/* Successfully fetched the requested stats from phyp */
> +	if (size != 0) {
> +		buff_stats->num_statistics =
> +			be32_to_cpu(buff_stats->num_statistics);
> +
> +		/* Transform the stats buffer values from BE to cpu native */
> +		for (i = 0, stats = buff_stats->scm_statistic;
> +		     i < buff_stats->num_statistics; ++i) {
> +			stats[i].statistic_value =
> +				be64_to_cpu(stats[i].statistic_value);
> +		}
> +		dev_dbg(&p->pdev->dev,
> +			"Performance stats returned %d stats\n",
> +			buff_stats->num_statistics);
> +	} else {
> +		/* Handle case where stat buffer size was requested */
> +		dev_dbg(&p->pdev->dev,
> +			"Performance stats size %ld\n", ret[0]);
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * Issue hcall to retrieve dimm health info and populate papr_scm_priv with the
>   * health information.
> @@ -631,6 +721,45 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
>  	return 0;
>  }
>  
> +static ssize_t perf_stats_show(struct device *dev,
> +			       struct device_attribute *attr, char *buf)
> +{
> +	int index, rc;
> +	struct seq_buf s;
> +	struct papr_scm_perf_stat *stat;
> +	struct papr_scm_perf_stats *stats;
> +	struct nvdimm *dimm = to_nvdimm(dev);
> +	struct papr_scm_priv *p = nvdimm_provider_data(dimm);
> +
> +	if (!p->len_stat_buffer)
> +		return -ENOENT;
> +
> +	/* Allocate the buffer for phyp where stats are written */
> +	stats = kzalloc(p->len_stat_buffer, GFP_KERNEL);
> +	if (!stats)
> +		return -ENOMEM;
> +
> +	/* Ask phyp to return all dimm perf stats */
> +	rc = drc_pmem_query_stats(p, stats, p->len_stat_buffer, 0, NULL);
> +	if (!rc) {
> +		/*
> +		 * Go through the returned output buffer and print stats and
> +		 * values. Since statistic_id is essentially a char string of
> +		 * 8 bytes, simply use the string format specifier to print it.
> +		 */
> +		seq_buf_init(&s, buf, PAGE_SIZE);
> +		for (index = 0, stat = stats->scm_statistic;
> +		     index < stats->num_statistics; ++index, ++stat) {
> +			seq_buf_printf(&s, "%.8s = 0x%016llX\n",
> +				       stat->statistic_id, stat->statistic_value);


That is raw number (statistic_id). Is that useful? Can we map them to user readable
strings? 

> +		}
> +	}
> +
> +	kfree(stats);
> +	return rc ? rc : seq_buf_used(&s);
> +}
> +DEVICE_ATTR_RO(perf_stats);
> +
>  static ssize_t flags_show(struct device *dev,
>  			  struct device_attribute *attr, char *buf)
>  {
> @@ -676,6 +805,7 @@ DEVICE_ATTR_RO(flags);
>  /* papr_scm specific dimm attributes */
>  static struct attribute *papr_nd_attributes[] = {
>  	&dev_attr_flags.attr,
> +	&dev_attr_perf_stats.attr,
>  	NULL,
>  };
>  
> @@ -696,6 +826,7 @@ 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;
> +	u64 stat_size;
>  
>  	p->bus_desc.ndctl = papr_scm_ndctl;
>  	p->bus_desc.module = THIS_MODULE;
> @@ -759,6 +890,14 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>  		dev_info(dev, "Region registered with target node %d and online node %d",
>  			 target_nid, online_nid);
>  
> +	/* Try retriving the stat buffer and see if its supported */
> +	if (!drc_pmem_query_stats(p, NULL, 0, 0, &stat_size)) {
> +		p->len_stat_buffer = (size_t)stat_size;
> +		dev_dbg(&p->pdev->dev, "Max perf-stat size %lu-bytes\n",
> +			p->len_stat_buffer);
> +	} else {
> +		dev_info(&p->pdev->dev, "Limited dimm stat info available\n");
> +	}
>  	return 0;
>  
>  err:	nvdimm_bus_unregister(p->bus);