Subject: Re: [PATCH v13 3/5] powerpc/perf: Add nest imc pmu support
To: mpe@ellerman.id.au
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Anju T Sudhakar <anju@linux.vnet.ibm.com>,
        Hemant Kumar <hemant@linux.vnet.ibm.com>
References: <1500413796-18340-1-git-send-email-maddy@linux.vnet.ibm.com>
 <1500413796-18340-4-git-send-email-maddy@linux.vnet.ibm.com>
From: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Date: Sat, 22 Jul 2017 12:42:06 +0530
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my bad, missed to change the authership of this patch.

From: Anju T Sudhakar <anju@linux.vnet.ibm.com>

On Wednesday 19 July 2017 03:06 AM, Madhavan Srinivasan wrote:
> Add support to register Nest In-Memory Collection pmu counters.
> Patch adds a new device file called "imc-pmu.c" under powerpc/perf
> folder to contain all the device pmu functions.
>
> Device tree parser code added to parse the pmu events information
> and create sysfs event attributes for the pmu.
>
> Cpumask attribute added along with Cpu hotplug online/offline functions
> specific for nest pmu. A new state "CPUHP_AP_PERF_POWERPC_NEST_IMC_ONLINE"
> added for the cpu hotplug callbacks. Error handle path frees the memory
> and unregisters the cpuhotplug callbacks.
>
> Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
> Signed-off-by: Hemant Kumar <hemant@linux.vnet.ibm.com>
> Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
> ---
>   arch/powerpc/perf/Makefile                |   1 +
>   arch/powerpc/perf/imc-pmu.c               | 748 ++++++++++++++++++++++++++++++
>   arch/powerpc/platforms/powernv/opal-imc.c |   5 +
>   include/linux/cpuhotplug.h                |   1 +
>   4 files changed, 755 insertions(+)
>   create mode 100644 arch/powerpc/perf/imc-pmu.c
>
> diff --git a/arch/powerpc/perf/Makefile b/arch/powerpc/perf/Makefile
> index 4d606b99a5cb..3f3a5ce66495 100644
> --- a/arch/powerpc/perf/Makefile
> +++ b/arch/powerpc/perf/Makefile
> @@ -8,6 +8,7 @@ obj64-$(CONFIG_PPC_PERF_CTRS)	+= power4-pmu.o ppc970-pmu.o power5-pmu.o \
>   				   isa207-common.o power8-pmu.o power9-pmu.o
>   obj32-$(CONFIG_PPC_PERF_CTRS)	+= mpc7450-pmu.o
>
> +obj-$(CONFIG_PPC_POWERNV)	+= imc-pmu.o
>   obj-$(CONFIG_FSL_EMB_PERF_EVENT) += core-fsl-emb.o
>   obj-$(CONFIG_FSL_EMB_PERF_EVENT_E500) += e500-pmu.o e6500-pmu.o
>
> diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
> new file mode 100644
> index 000000000000..6e00ea7358a2
> --- /dev/null
> +++ b/arch/powerpc/perf/imc-pmu.c
> @@ -0,0 +1,748 @@
> +/*
> + * In-Memory Collection (IMC) Performance Monitor counter support.
> + *
> + * Copyright (C) 2017 Madhavan Srinivasan, IBM Corporation.
> + *           (C) 2017 Anju T Sudhakar, IBM Corporation.
> + *           (C) 2017 Hemant K Shaw, IBM Corporation.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version
> + * 2 of the License, or later version.
> + */
> +#include <linux/perf_event.h>
> +#include <linux/slab.h>
> +#include <asm/opal.h>
> +#include <asm/imc-pmu.h>
> +#include <asm/cputhreads.h>
> +#include <asm/smp.h>
> +#include <linux/string.h>
> +
> +//Nest imc data structures and variable
> +/*
> + * Used to avoid races in counting the nest-pmu units during hotplug
> + * register and unregister
> + */
> +static DEFINE_MUTEX(nest_init_lock);
> +static DEFINE_PER_CPU(struct imc_pmu_ref *, local_nest_imc_refc);
> +static struct imc_pmu *per_nest_pmu_arr[IMC_MAX_PMUS];
> +static cpumask_t nest_imc_cpumask;
> +struct imc_pmu_ref *nest_imc_refc;
> +static int nest_pmus;
> +
> +struct imc_pmu *imc_event_to_pmu(struct perf_event *event)
> +{
> +	return container_of(event->pmu, struct imc_pmu, pmu);
> +}
> +
> +PMU_FORMAT_ATTR(event, "config:0-40");
> +PMU_FORMAT_ATTR(offset, "config:0-31");
> +PMU_FORMAT_ATTR(rvalue, "config:32");
> +PMU_FORMAT_ATTR(mode, "config:33-40");
> +static struct attribute *imc_format_attrs[] = {
> +	&format_attr_event.attr,
> +	&format_attr_offset.attr,
> +	&format_attr_rvalue.attr,
> +	&format_attr_mode.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group imc_format_group = {
> +	.name = "format",
> +	.attrs = imc_format_attrs,
> +};
> +
> +/* Get the cpumask printed to a buffer "buf" */
> +static ssize_t imc_pmu_cpumask_get_attr(struct device *dev,
> +					struct device_attribute *attr,
> +					char *buf)
> +{
> +	struct pmu *pmu = dev_get_drvdata(dev);
> +	struct imc_pmu *imc_pmu = container_of(pmu, struct imc_pmu, pmu);
> +	cpumask_t *active_mask;
> +
> +	/* Subsequenct patch will add more pmu types here */
> +	switch(imc_pmu->domain){
> +	case IMC_DOMAIN_NEST:
> +		active_mask = &nest_imc_cpumask;
> +		break;
> +	default:
> +		return 0;
> +	}
> +
> +	return cpumap_print_to_pagebuf(true, buf, active_mask);
> +}
> +
> +static DEVICE_ATTR(cpumask, S_IRUGO, imc_pmu_cpumask_get_attr, NULL);
> +
> +static struct attribute *imc_pmu_cpumask_attrs[] = {
> +	&dev_attr_cpumask.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group imc_pmu_cpumask_attr_group = {
> +	.attrs = imc_pmu_cpumask_attrs,
> +};
> +
> +/* device_str_attr_create : Populate event "name" and string "str" in attribute */
> +static struct attribute *device_str_attr_create(const char *name, const char *str)
> +{
> +	struct perf_pmu_events_attr *attr;
> +
> +	attr = kzalloc(sizeof(*attr), GFP_KERNEL);
> +	if (!attr)
> +		return NULL;
> +	sysfs_attr_init(&attr->attr.attr);
> +
> +	attr->event_str = str;
> +	attr->attr.attr.name = name;
> +	attr->attr.attr.mode = 0444;
> +	attr->attr.show = perf_event_sysfs_show;
> +
> +	return &attr->attr.attr;
> +}
> +
> +struct imc_events *imc_parse_event(struct device_node *np, const char *scale,
> +				  const char *unit, const char *prefix, u32 base)
> +{
> +	struct imc_events *event;
> +	const char *s;
> +	u32 reg;
> +
> +	event = kzalloc(sizeof(struct imc_events), GFP_KERNEL);
> +	if (!event)
> +		return NULL;
> +
> +	if (of_property_read_u32(np, "reg", &reg))
> +		goto error;
> +	/* Add the base_reg value to the "reg" */
> +	event->value = base + reg;
> +
> +	if (of_property_read_string(np, "event-name", &s))
> +		goto error;
> +
> +	event->name = kasprintf(GFP_KERNEL, "%s%s", prefix, s);
> +	if (!event->name)
> +		goto error;
> +
> +	if (of_property_read_string(np, "scale", &s))
> +		s = scale;
> +
> +	if (s) {
> +		event->scale = kstrdup(s, GFP_KERNEL);
> +		if (!event->scale)
> +			goto error;
> +	}
> +
> +	if (of_property_read_string(np, "unit", &s))
> +		s = unit;
> +
> +	if (s) {
> +		event->unit = kstrdup(s, GFP_KERNEL);
> +		if (!event->unit)
> +			goto error;
> +	}
> +
> +	return event;
> +error:
> +	kfree(event->unit);
> +	kfree(event->scale);
> +	kfree(event->name);
> +	kfree(event);
> +
> +	return NULL;
> +}
> +
> +/*
> + * update_events_in_group: Update the "events" information in an attr_group
> + *                         and assign the attr_group to the pmu "pmu".
> + */
> +static int update_events_in_group(struct device_node *node, struct imc_pmu *pmu)
> +{
> +	struct attribute_group *attr_group;
> +	struct attribute **attrs, *dev_str;
> +	struct device_node *np, *pmu_events;
> +	struct imc_events *ev;
> +	u32 handle, base_reg;
> +	int i=0, j=0, ct;
> +	const char *prefix, *g_scale, *g_unit;
> +	const char *ev_val_str, *ev_scale_str, *ev_unit_str;
> +
> +	if (!of_property_read_u32(node, "events", &handle))
> +		pmu_events = of_find_node_by_phandle(handle);
> +	else
> +		return 0;
> +
> +	/* Did not find any node with a given phandle */
> +	if (!pmu_events)
> +		return 0;
> +
> +	/* Get a count of number of child nodes */
> +	ct = of_get_child_count(pmu_events);
> +
> +	/* Get the event prefix */
> +	if (of_property_read_string(node, "events-prefix", &prefix))
> +		return 0;
> +
> +	/* Get a global unit and scale data if available */
> +	if (of_property_read_string(node, "scale", &g_scale))
> +		g_scale = NULL;
> +
> +	if (of_property_read_string(node, "unit", &g_unit))
> +		g_unit = NULL;
> +
> +	/* "reg" property gives out the base offset of the counters data */
> +	of_property_read_u32(node, "reg", &base_reg);
> +
> +	/* Allocate memory for the events */
> +	pmu->events = kcalloc(ct, sizeof(struct imc_events), GFP_KERNEL);
> +	if (!pmu->events)
> +		return -ENOMEM;
> +
> +	ct = 0;
> +	/* Parse the events and update the struct */
> +	for_each_child_of_node(pmu_events, np) {
> +		ev = imc_parse_event(np, g_scale, g_unit, prefix, base_reg);
> +		if (ev)
> +			pmu->events[ct++] = ev;
> +	}
> +
> +	/* Allocate memory for attribute group */
> +	attr_group = kzalloc(sizeof(*attr_group), GFP_KERNEL);
> +	if (!attr_group)
> +		return -ENOMEM;
> +
> +	/*
> +	 * Allocate memory for attributes.
> +	 * Since we have count of events for this pmu, we also allocate
> +	 * memory for the scale and unit attribute for now.
> +	 * "ct" has the total event structs added from the events-parent node.
> +	 * So allocate three times the "ct" (this includes event, event_scale and
> +	 * event_unit).
> +	 */
> +	attrs = kcalloc(((ct * 3) + 1), sizeof(struct attribute *), GFP_KERNEL);
> +	if (!attrs) {
> +		kfree(attr_group);
> +		kfree(pmu->events);
> +		return -ENOMEM;
> +	}
> +
> +	attr_group->name = "events";
> +	attr_group->attrs = attrs;
> +	do {
> +		ev_val_str = kasprintf(GFP_KERNEL, "event=0x%x", pmu->events[i]->value);
> +		dev_str = device_str_attr_create(pmu->events[i]->name, ev_val_str);
> +		if (!dev_str)
> +			continue;
> +
> +		attrs[j++] = dev_str;
> +		if (pmu->events[i]->scale) {
> +			ev_scale_str = kasprintf(GFP_KERNEL, "%s.scale",pmu->events[i]->name);
> +			dev_str = device_str_attr_create(ev_scale_str, pmu->events[i]->scale);
> +			if (!dev_str)
> +				continue;
> +
> +			attrs[j++] = dev_str;
> +		}
> +
> +		if (pmu->events[i]->unit) {
> +			ev_unit_str = kasprintf(GFP_KERNEL, "%s.unit",pmu->events[i]->name);
> +			dev_str = device_str_attr_create(ev_unit_str, pmu->events[i]->unit);
> +			if (!dev_str)
> +				continue;
> +
> +			attrs[j++] = dev_str;
> +		}
> +	} while (++i < ct);
> +
> +	/* Save the event attribute */
> +	pmu->attr_groups[IMC_EVENT_ATTR] = attr_group;
> +
> +	kfree(pmu->events);
> +	return 0;
> +}
> +
> +/* get_nest_pmu_ref: Return the imc_pmu_ref struct for the given node */
> +static struct imc_pmu_ref *get_nest_pmu_ref(int cpu)
> +{
> +	return per_cpu(local_nest_imc_refc, cpu);
> +}
> +
> +static void nest_change_cpu_context(int old_cpu, int new_cpu)
> +{
> +	struct imc_pmu **pn = per_nest_pmu_arr;
> +	int i;
> +
> +	if (old_cpu < 0 || new_cpu < 0)
> +		return;
> +
> +	for (i = 0; *pn && i < IMC_MAX_PMUS; i++, pn++)
> +		perf_pmu_migrate_context(&(*pn)->pmu, old_cpu, new_cpu);
> +}
> +
> +static int ppc_nest_imc_cpu_offline(unsigned int cpu)
> +{
> +	int nid, target = -1;
> +	const struct cpumask *l_cpumask;
> +	struct imc_pmu_ref *ref;
> +
> +	/*
> +	 * Check in the designated list for this cpu. Dont bother
> +	 * if not one of them.
> +	 */
> +	if (!cpumask_test_and_clear_cpu(cpu, &nest_imc_cpumask))
> +		return 0;
> +
> +	/*
> +	 * Now that this cpu is one of the designated,
> +	 * find a next cpu a) which is online and b) in same chip.
> +	 */
> +	nid = cpu_to_node(cpu);
> +	l_cpumask = cpumask_of_node(nid);
> +	target = cpumask_any_but(l_cpumask, cpu);
> +
> +	/*
> +	 * Update the cpumask with the target cpu and
> +	 * migrate the context if needed
> +	 */
> +	if (target >= 0 && target < nr_cpu_ids) {
> +		cpumask_set_cpu(target, &nest_imc_cpumask);
> +		nest_change_cpu_context(cpu, target);
> +	} else {
> +		opal_imc_counters_stop(OPAL_IMC_COUNTERS_NEST,
> +				       get_hard_smp_processor_id(cpu));
> +		/*
> +		 * If this is the last cpu in this chip then, skip the reference
> +		 * count mutex lock and make the reference count on this chip zero.
> +		 */
> +		ref = get_nest_pmu_ref(cpu);
> +		if (!ref)
> +			return -EINVAL;
> +
> +		ref->refc = 0;
> +	}
> +	return 0;
> +}
> +
> +static int ppc_nest_imc_cpu_online(unsigned int cpu)
> +{
> +	const struct cpumask *l_cpumask;
> +	static struct cpumask tmp_mask;
> +	int res;
> +
> +	/* Get the cpumask of this node */
> +	l_cpumask = cpumask_of_node(cpu_to_node(cpu));
> +
> +	/*
> +	 * If this is not the first online CPU on this node, then
> +	 * just return.
> +	 */
> +	if (cpumask_and(&tmp_mask, l_cpumask, &nest_imc_cpumask))
> +		return 0;
> +
> +	/*
> +	 * If this is the first online cpu on this node
> +	 * disable the nest counters by making an OPAL call.
> +	 */
> +	res = opal_imc_counters_stop(OPAL_IMC_COUNTERS_NEST,
> +				     get_hard_smp_processor_id(cpu));
> +	if (res)
> +		return res;
> +
> +	/* Make this CPU the designated target for counter collection */
> +	cpumask_set_cpu(cpu, &nest_imc_cpumask);
> +	return 0;
> +}
> +
> +static int nest_pmu_cpumask_init(void)
> +{
> +	return cpuhp_setup_state(CPUHP_AP_PERF_POWERPC_NEST_IMC_ONLINE,
> +				 "perf/powerpc/imc:online",
> +				 ppc_nest_imc_cpu_online,
> +				 ppc_nest_imc_cpu_offline);
> +}
> +
> +static void nest_imc_counters_release(struct perf_event *event)
> +{
> +	int rc, node_id;
> +	struct imc_pmu_ref *ref;
> +
> +	if (event->cpu < 0)
> +		return;
> +
> +	node_id = cpu_to_node(event->cpu);
> +
> +	/*
> +	 * See if we need to disable the nest PMU.
> +	 * If no events are currently in use, then we have to take a
> +	 * mutex to ensure that we don't race with another task doing
> +	 * enable or disable the nest counters.
> +	 */
> +	ref = get_nest_pmu_ref(event->cpu);
> +	if (!ref)
> +		return;
> +
> +	/* Take the mutex lock for this node and then decrement the reference count */
> +	mutex_lock(&ref->lock);
> +	ref->refc--;
> +	if (ref->refc == 0) {
> +		rc = opal_imc_counters_stop(OPAL_IMC_COUNTERS_NEST,
> +					    get_hard_smp_processor_id(event->cpu));
> +		if (rc) {
> +			mutex_unlock(&nest_imc_refc[node_id].lock);
> +			pr_err("nest-imc: Unable to stop the counters for core %d\n", node_id);
> +			return;
> +		}
> +	} else if (ref->refc < 0) {
> +		WARN(1, "nest-imc: Invalid event reference count\n");
> +		ref->refc = 0;
> +	}
> +	mutex_unlock(&ref->lock);
> +}
> +
> +static int nest_imc_event_init(struct perf_event *event)
> +{
> +	int chip_id, rc, node_id;
> +	u32 l_config, config = event->attr.config;
> +	struct imc_mem_info *pcni;
> +	struct imc_pmu *pmu;
> +	struct imc_pmu_ref *ref;
> +	bool flag = false;
> +
> +	if (event->attr.type != event->pmu->type)
> +		return -ENOENT;
> +
> +	/* Sampling not supported */
> +	if (event->hw.sample_period)
> +		return -EINVAL;
> +
> +	/* unsupported modes and filters */
> +	if (event->attr.exclude_user   ||
> +	    event->attr.exclude_kernel ||
> +	    event->attr.exclude_hv     ||
> +	    event->attr.exclude_idle   ||
> +	    event->attr.exclude_host   ||
> +	    event->attr.exclude_guest)
> +		return -EINVAL;
> +
> +	if (event->cpu < 0)
> +		return -EINVAL;
> +
> +	pmu = imc_event_to_pmu(event);
> +
> +	/* Sanity check for config (event offset) */
> +	if ((config & IMC_EVENT_OFFSET_MASK) > pmu->counter_mem_size)
> +		return -EINVAL;
> +
> +	/*
> +	 * Nest HW counter memory resides in a per-chip reserve-memory (HOMER).
> +	 * Get the base memory addresss for this cpu.
> +	 */
> +	chip_id = topology_physical_package_id(event->cpu);
> +	pcni = pmu->mem_info;
> +	do {
> +		if (pcni->id == chip_id) {
> +			flag = true;
> +			break;
> +		}
> +		pcni++;
> +	} while (pcni);
> +
> +	if (!flag)
> +		return -ENODEV;
> +
> +	/*
> +	 * Add the event offset to the base address.
> +	 */
> +	l_config = config & IMC_EVENT_OFFSET_MASK;
> +	event->hw.event_base = (u64)pcni->vbase + l_config;
> +	node_id = cpu_to_node(event->cpu);
> +
> +	/*
> +	 * Get the imc_pmu_ref struct for this node.
> +	 * Take the mutex lock and then increment the count of nest pmu events
> +	 * inited.
> +	 */
> +	ref = get_nest_pmu_ref(event->cpu);
> +	if (!ref)
> +		return -EINVAL;
> +
> +	mutex_lock(&ref->lock);
> +	if (ref->refc == 0) {
> +		rc = opal_imc_counters_start(OPAL_IMC_COUNTERS_NEST,
> +					     get_hard_smp_processor_id(event->cpu));
> +		if (rc) {
> +			mutex_unlock(&nest_imc_refc[node_id].lock);
> +			pr_err("nest-imc: Unable to start the counters for node %d\n",
> +									node_id);
> +			return rc;
> +		}
> +	}
> +	++ref->refc;
> +	mutex_unlock(&ref->lock);
> +
> +	event->destroy = nest_imc_counters_release;
> +	return 0;
> +}
> +
> +static u64 * get_event_base_addr(struct perf_event *event)
> +{
> +	/*
> +	 * Subsequent patch will add code to detect caller imc pmu
> +	 * and return accordingly.
> +	 */
> +	return (u64 *)event->hw.event_base;
> +}
> +
> +static u64 imc_read_counter(struct perf_event *event)
> +{
> +	u64 *addr, data;
> +
> +	/*
> +	 * In-Memory Collection (IMC) counters are free flowing counters.
> +	 * So we take a snapshot of the counter value on enable and save it
> +	 * to calculate the delta at later stage to present the event counter
> +	 * value.
> +	 */
> +	addr = get_event_base_addr(event);
> +	data = be64_to_cpu(READ_ONCE(*addr));
> +	local64_set(&event->hw.prev_count, data);
> +
> +	return data;
> +}
> +
> +static void imc_event_update(struct perf_event *event)
> +{
> +	u64 counter_prev, counter_new, final_count;
> +
> +	counter_prev = local64_read(&event->hw.prev_count);
> +	counter_new = imc_read_counter(event);
> +	final_count = counter_new - counter_prev;
> +
> +	/* Update the delta to the event count */
> +	local64_add(final_count, &event->count);
> +}
> +
> +static void imc_event_start(struct perf_event *event, int flags)
> +{
> +	/*
> +	 * In Memory Counters are free flowing counters. HW or the microcode
> +	 * keeps adding to the counter offset in memory. To get event
> +	 * counter value, we snapshot the value here and we calculate
> +	 * delta at later point.
> +	 */
> +	imc_read_counter(event);
> +}
> +
> +static void imc_event_stop(struct perf_event *event, int flags)
> +{
> +	/*
> +	 * Take a snapshot and calculate the delta and update
> +	 * the event counter values.
> +	 */
> +	imc_event_update(event);
> +}
> +
> +static int imc_event_add(struct perf_event *event, int flags)
> +{
> +	if (flags & PERF_EF_START)
> +		imc_event_start(event, flags);
> +
> +	return 0;
> +}
> +
> +/* update_pmu_ops : Populate the appropriate operations for "pmu" */
> +static int update_pmu_ops(struct imc_pmu *pmu)
> +{
> +	pmu->pmu.task_ctx_nr = perf_invalid_context;
> +	pmu->pmu.add = imc_event_add;
> +	pmu->pmu.del = imc_event_stop;
> +	pmu->pmu.start = imc_event_start;
> +	pmu->pmu.stop = imc_event_stop;
> +	pmu->pmu.read = imc_event_update;
> +	pmu->pmu.attr_groups = pmu->attr_groups;
> +	pmu->attr_groups[IMC_FORMAT_ATTR] = &imc_format_group;
> +
> +	/* Subsequenct patch will add more pmu types here */
> +	switch (pmu->domain) {
> +	case IMC_DOMAIN_NEST:
> +		pmu->pmu.event_init = nest_imc_event_init;
> +		pmu->attr_groups[IMC_CPUMASK_ATTR] = &imc_pmu_cpumask_attr_group;
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	return 0;
> +}
> +
> +/* init_nest_pmu_ref: Initialize the imc_pmu_ref struct for all the nodes */
> +static int init_nest_pmu_ref(void)
> +{
> +	int nid, i, cpu;
> +
> +	nest_imc_refc = kcalloc(num_possible_nodes(), sizeof(*nest_imc_refc),
> +								GFP_KERNEL);
> +
> +	if (!nest_imc_refc)
> +		return -ENOMEM;
> +
> +	i = 0;
> +	for_each_node(nid) {
> +		/*
> +		 * Mutex lock to avoid races while tracking the number of
> +		 * sessions using the chip's nest pmu units.
> +		 */
> +		mutex_init(&nest_imc_refc[i].lock);
> +
> +		/*
> +		 * Loop to init the "id" with the node_id. Variable "i" initialized to
> +		 * 0 and will be used as index to the array. "i" will not go off the
> +		 * end of the array since the "for_each_node" loops for "N_POSSIBLE"
> +		 * nodes only.
> +		 */
> +		nest_imc_refc[i++].id = nid;
> +	}
> +
> +	/*
> +	 * Loop to init the per_cpu "local_nest_imc_refc" with the proper
> +	 * "nest_imc_refc" index. This makes get_nest_pmu_ref() alot simple.
> +	 */
> +	for_each_possible_cpu(cpu) {
> +		nid = cpu_to_node(cpu);
> +		for_each_online_node(i) {
> +			if (nest_imc_refc[i].id == nid) {
> +				per_cpu(local_nest_imc_refc, cpu) = &nest_imc_refc[i];
> +				break;
> +			}
> +		}
> +	}
> +	return 0;
> +}
> +
> +/*
> + * Common function to unregister cpu hotplug callback and
> + * free the memory.
> + * TODO: Need to handle pmu unregistering, which will be
> + * done in followup series.
> + */
> +static void imc_common_cpuhp_mem_free(struct imc_pmu *pmu_ptr)
> +{
> +	if (pmu_ptr->domain == IMC_DOMAIN_NEST) {
> +		mutex_unlock(&nest_init_lock);
> +		if (nest_pmus == 1) {
> +			cpuhp_remove_state(CPUHP_AP_PERF_POWERPC_NEST_IMC_ONLINE);
> +			kfree(nest_imc_refc);
> +		}
> +
> +		if (nest_pmus > 0)
> +			nest_pmus--;
> +		mutex_unlock(&nest_init_lock);
> +	}
> +
> +	/* Only free the attr_groups which are dynamically allocated  */
> +	kfree(pmu_ptr->attr_groups[IMC_EVENT_ATTR]->attrs);
> +	kfree(pmu_ptr->attr_groups[IMC_EVENT_ATTR]);
> +	kfree(pmu_ptr);
> +	return;
> +}
> +
> +
> +/*
> + * imc_mem_init : Function to support memory allocation for core imc.
> + */
> +static int imc_mem_init(struct imc_pmu *pmu_ptr, struct device_node *parent,
> +								int pmu_index)
> +{
> +	const char *s;
> +
> +	if (of_property_read_string(parent, "name", &s))
> +		return -ENODEV;
> +
> +	/* Subsequenct patch will add more pmu types here */
> +	switch (pmu_ptr->domain) {
> +	case IMC_DOMAIN_NEST:
> +		/* Update the pmu name */
> +		pmu_ptr->pmu.name = kasprintf(GFP_KERNEL, "%s%s_imc", "nest_", s);
> +		if (!pmu_ptr->pmu.name)
> +			return -ENOMEM;
> +
> +		/* Needed for hotplug/migration */
> +		per_nest_pmu_arr[pmu_index] = pmu_ptr;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * init_imc_pmu : Setup and register the IMC pmu device.
> + *
> + * @parent:	Device tree unit node
> + * @pmu_ptr:	memory allocated for this pmu
> + * @pmu_idx:	Count of nest pmc registered
> + *
> + * init_imc_pmu() setup pmu cpumask and registers for a cpu hotplug callback.
> + * Handles failure cases and accordingly frees memory.
> + */
> +int init_imc_pmu(struct device_node *parent, struct imc_pmu *pmu_ptr, int pmu_idx)
> +{
> +	int ret;
> +
> +	ret = imc_mem_init(pmu_ptr, parent, pmu_idx);
> +	if (ret)
> +		goto err_free;
> +
> +	/* Subsequenct patch will add more pmu types here */
> +	switch (pmu_ptr->domain) {
> +	case IMC_DOMAIN_NEST:
> +		/*
> +		* Nest imc pmu need only one cpu per chip, we initialize the
> +		* cpumask for the first nest imc pmu and use the same for the
> +		* rest. To handle the cpuhotplug callback unregister, we track
> +		* the number of nest pmus in "nest_pmus".
> +		*/
> +		mutex_lock(&nest_init_lock);
> +		if (nest_pmus == 0) {
> +			ret = init_nest_pmu_ref();
> +			if (ret) {
> +				mutex_unlock(&nest_init_lock);
> +				goto err_free;
> +			}
> +			/* Register for cpu hotplug notification. */
> +			ret = nest_pmu_cpumask_init();
> +			if (ret) {
> +				mutex_unlock(&nest_init_lock);
> +				goto err_free;
> +			}
> +		}
> +		nest_pmus++;
> +		mutex_unlock(&nest_init_lock);
> +		break;
> +	default:
> +		return  -1;	/* Unknown domain */
> +	}
> +
> +	ret = update_events_in_group(parent, pmu_ptr);
> +	if (ret)
> +		goto err_free;
> +
> +	ret = update_pmu_ops(pmu_ptr);
> +	if (ret)
> +		goto err_free;
> +
> +	ret = perf_pmu_register(&pmu_ptr->pmu, pmu_ptr->pmu.name, -1);
> +	if (ret)
> +		goto err_free;
> +
> +	pr_info("%s performance monitor hardware support registered\n",
> +							pmu_ptr->pmu.name);
> +
> +	return 0;
> +
> +err_free:
> +	imc_common_cpuhp_mem_free(pmu_ptr);
> +	return ret;
> +}
> diff --git a/arch/powerpc/platforms/powernv/opal-imc.c b/arch/powerpc/platforms/powernv/opal-imc.c
> index f57a6fbd3f57..b903bf5e6006 100644
> --- a/arch/powerpc/platforms/powernv/opal-imc.c
> +++ b/arch/powerpc/platforms/powernv/opal-imc.c
> @@ -108,6 +108,11 @@ static int imc_pmu_create(struct device_node *parent, int pmu_index, int domain)
>   		}
>   	}
>
> +	/* Function to register IMC pmu */
> +	ret = init_imc_pmu(parent, pmu_ptr, pmu_index);
> +	if (ret)
> +		pr_err("IMC PMU %s Register failed\n", pmu_ptr->pmu.name);
> +
>   	return 0;
>
>   free_pmu:
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index b56573bf440d..0853a14b1fa1 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -139,6 +139,7 @@ enum cpuhp_state {
>   	CPUHP_AP_PERF_ARM_L2X0_ONLINE,
>   	CPUHP_AP_PERF_ARM_QCOM_L2_ONLINE,
>   	CPUHP_AP_PERF_ARM_QCOM_L3_ONLINE,
> +	CPUHP_AP_PERF_POWERPC_NEST_IMC_ONLINE,
>   	CPUHP_AP_WORKQUEUE_ONLINE,
>   	CPUHP_AP_RCUTREE_ONLINE,
>   	CPUHP_AP_ONLINE_DYN,