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Date:   Tue, 04 Apr 2017 11:41:53 +1000
From:   Daniel Axtens <dja@...ens.net>
To:     Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>, mpe@...erman.id.au
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        ego@...ux.vnet.ibm.com, bsingharora@...il.com,
        benh@...nel.crashing.org, paulus@...ba.org, anton@...ba.org,
        sukadev@...ux.vnet.ibm.com, mikey@...ling.org,
        stewart@...ux.vnet.ibm.com, eranian@...gle.com,
        Hemant Kumar <hemant@...ux.vnet.ibm.com>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
Subject: Re: [PATCH v6 03/11] powerpc/powernv: Detect supported IMC units and its events

Madhavan Srinivasan <maddy@...ux.vnet.ibm.com> writes:

> From: Hemant Kumar <hemant@...ux.vnet.ibm.com>
>
> Parse device tree to detect IMC units. Traverse through each IMC unit
> node to find supported events and corresponding unit/scale files (if any).
>
> Here is the DTS file for reference:
>
> 	https://github.com/open-power/ima-catalog/blob/master/81E00612.4E0100.dts
>
> The device tree for IMC counters starts at the node "imc-counters".
> This node contains all the IMC PMU nodes and event nodes
> for these IMC PMUs. The PMU nodes have an "events" property which has a
> phandle value for the actual events node. The events are separated from
> the PMU nodes to abstract out the common events. For example, PMU node
> "mcs0", "mcs1" etc. will contain a pointer to "nest-mcs-events" since,
> the events are common between these PMUs. These events have a different
> prefix based on their relation to different PMUs, and hence, the PMU
> nodes themselves contain an "events-prefix" property. The value for this
> property concatenated to the event name, forms the actual event
> name. Also, the PMU have a "reg" field as the base offset for the events
> which belong to this PMU. This "reg" field is added to an event in the
> "events" node, which gives us the location of the counter data. Kernel
> code uses this offset as event configuration value.

This is probably because I haven't looked at this area recently, but
what do you mean by 'event configuration value'? If I understand
correctly, you're saying something like "kernel code stores this
calculated location in the event configuration data" - is that about
right?

Apologies if this is a dumb question.

>
> Device tree parser code also looks for scale/unit property in the event
> node and passes on the value as an event attr for perf interface to use
> in the post processing by the perf tool. Some PMUs may have common scale
> and unit properties which implies that all events supported by this PMU
> inherit the scale and unit properties of the PMU itself. For those
> events, we need to set the common unit and scale values.
>
> For failure to initialize any unit or any event, disable that unit and
> continue setting up the rest of them.
>
> Signed-off-by: Hemant Kumar <hemant@...ux.vnet.ibm.com>
> Signed-off-by: Anju T Sudhakar <anju@...ux.vnet.ibm.com>
> Signed-off-by: Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
> ---
>  arch/powerpc/platforms/powernv/opal-imc.c | 386 ++++++++++++++++++++++++++++++
>  1 file changed, 386 insertions(+)
>
> diff --git a/arch/powerpc/platforms/powernv/opal-imc.c b/arch/powerpc/platforms/powernv/opal-imc.c
> index c476d596c6a8..ba0203e669c0 100644
> --- a/arch/powerpc/platforms/powernv/opal-imc.c
> +++ b/arch/powerpc/platforms/powernv/opal-imc.c
> @@ -33,6 +33,388 @@
>  #include <asm/imc-pmu.h>
>  
>  struct perchip_nest_info nest_perchip_info[IMC_MAX_CHIPS];
> +struct imc_pmu *per_nest_pmu_arr[IMC_MAX_PMUS];
> +
> +static int imc_event_info(char *name, struct imc_events *events)
This seems to be an allocation/init function: should that be reflected
in the name?

> +{
> +	char *buf;
> +
> +	/* memory for content */
> +	buf = kzalloc(IMC_MAX_PMU_NAME_LEN, GFP_KERNEL);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	events->ev_name = name;
We trust the name will never become a dangling pointer? We don't need to
duplicate it?

Should the pointer be const?

> +	events->ev_value = buf;
> +	return 0;
> +}
> +
> +static int imc_event_info_str(struct property *pp, char *name,
> +			       struct imc_events *events)
This creates and sets an initial value based on a property, ...

> +static int imc_event_info_val(char *name, u32 val,
> +			      struct imc_events *events)
... this creates and sets based on a u32.

Could you call them something that suggests their purpose a bit better?
Maybe event_info_from_{property,val}? 

> +{
> +	int ret;
> +
> +	ret = imc_event_info(name, events);
> +	if (ret)
> +		return ret;
> +	sprintf(events->ev_value, "event=0x%x", val);
> +
> +	return 0;
> +}
> +
> +static int set_event_property(struct property *pp, char *event_prop,
> +			      struct imc_events *events, char *ev_name)
> +{
> +	char *buf;
> +	int ret;
> +
> +	buf = kzalloc(IMC_MAX_PMU_NAME_LEN, GFP_KERNEL);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	sprintf(buf, "%s.%s", ev_name, event_prop);
> +	ret = imc_event_info_str(pp, buf, events);
> +	if (ret) {
> +		kfree(events->ev_name);
> +		kfree(events->ev_value);
How do you know the buffer for ev_value was successfully allocated? Can
you be sure it is safe to free? (Consider imc_event_info returning -ENOMEM)

> +	}
> +
> +	return ret;
> +}
> +
> +/*
> + * imc_events_node_parser: Parse the event node "dev" and assign the parsed
> + *                         information to event "events".
> + *
> + * Parses the "reg" property of this event. "reg" gives us the event offset.
> + * Also, parse the "scale" and "unit" properties, if any.
> + */
> +static int imc_events_node_parser(struct device_node *dev,
> +				  struct imc_events *events,
> +				  struct property *event_scale,
> +				  struct property *event_unit,
> +				  struct property *name_prefix,
> +				  u32 reg)
> +{
> +	struct property *name, *pp;
> +	char *ev_name;
> +	u32 val;
> +	int idx = 0, ret;
> +
> +	if (!dev)
> +		return -EINVAL;
> +
> +	/*
> +	 * Loop through each property of an event node
> +	 */
> +	name = of_find_property(dev, "event-name", NULL);
> +	if (!name)
> +		return -ENODEV;
> +
> +	if (!name->value ||
> +	  (strnlen(name->value, name->length) == name->length) ||
> +	  (name->length > IMC_MAX_PMU_NAME_LEN))
> +		return -EINVAL;
> +
> +	ev_name = kzalloc(IMC_MAX_PMU_NAME_LEN, GFP_KERNEL);
> +	if (!ev_name)
> +		return -ENOMEM;
I see you allocating memory here and in set_event_property for the
name. Would it be better to move that into imc_event_info and make that
function responsible for the whole set of allocations regarding the
event?

(I'm happy to be talked out of this - it just seems like it would make
it much easier to reason about the lifecycles of the memory allocations.)

> +
> +	snprintf(ev_name, IMC_MAX_PMU_NAME_LEN, "%s%s",
> +		 (char *)name_prefix->value,
> +		 (char *)name->value);
> +
> +	/*
> +	 * Parse each property of this event node "dev". Property "reg" has
> +	 * the offset which is assigned to the event name. Other properties
> +	 * like "scale" and "unit" are assigned to event.scale and event.unit
> +	 * accordingly.
> +	 */
> +	for_each_property_of_node(dev, pp) {
> +		/*
> +		 * If there is an issue in parsing a single property of
> +		 * this event, we just clean up the buffers, but we still
> +		 * continue to parse.
> +		 */
> +		if (strncmp(pp->name, "reg", 3) == 0) {
> +			of_property_read_u32(dev, pp->name, &val);
> +			val += reg;
> +			ret = imc_event_info_val(ev_name, val, &events[idx]);
> +			if (ret) {
> +				kfree(events[idx].ev_name);
> +				kfree(events[idx].ev_value);
> +				continue;
> +			}
> +			/*
> +			 * If the common scale and unit properties available,
> +			 * then, assign them to this event
> +			 */
> +			if (event_scale) {
> +				idx++;
> +				ret = set_event_property(event_scale, "scale",
> +							 &events[idx],
> +							 ev_name);
> +				if (ret)
> +					continue;
> +				idx++;

Why do we increment the idx an extra two times if event_scale is
provided? We don't do that for the other ones...

> +			}
> +			if (event_unit) {
> +				ret = set_event_property(event_unit, "unit",
> +							 &events[idx],
> +							 ev_name);
> +				if (ret)
> +					continue;
> +			}
> +			idx++;
> +		} else if (strncmp(pp->name, "unit", 4) == 0) {
> +			ret = set_event_property(pp, "unit", &events[idx],
> +						 ev_name);
> +			if (ret)
> +				continue;
> +			idx++;
> +		} else if (strncmp(pp->name, "scale", 5) == 0) {
> +			ret = set_event_property(pp, "scale", &events[idx],
> +						 ev_name);
> +			if (ret)
> +				continue;
> +			idx++;
> +		}
> +	}

I find it really difficult to convince myself of the control flow in
that loop.

In particular, the comment at the top claims:
> +		 * If there is an issue in parsing a single property of
> +		 * this event, we just clean up the buffers, but we still
> +		 * continue to parse.

I am not quite sure precisely what that means. I first thought it meant
that if you cannot parse one of the properties of the event
(scale/unit), you would clean up the entire event, and parse the next
entire event. It looks like the code in fact simply cleans up that
*property* and continues to parse other properties.

Does that make sense to do? If you can't parse the scale of an event for
instance, does it make sense to continue with the rest of that event?

Initially I was concerned that 'continue' wasn't sufficient to even
clean up the property, but I worked through the error conditions of
set_event_property and now I am satisfied.

> +
> +	return idx;
> +}
> +
> +/*
> + * imc_get_domain : Returns the domain for pmu "pmu_dev".
> + */
> +int imc_get_domain(struct device_node *pmu_dev)
> +{
> +	if (of_device_is_compatible(pmu_dev, IMC_DTB_NEST_COMPAT))
> +		return IMC_DOMAIN_NEST;
> +	else
> +		return IMC_DOMAIN_UNKNOWN;
> +}
> +
> +/*
> + * get_nr_children : Returns the number of children for a pmu device node.
> + */
> +static int get_nr_children(struct device_node *pmu_node)
> +{
> +	struct device_node *child;
> +	int i = 0;
> +
> +	for_each_child_of_node(pmu_node, child)
> +		i++;
> +	return i;
> +}
> +
> +/*
> + * imc_free_events : Cleanup the "events" list having "nr_entries" entries.
> + */
> +static void imc_free_events(struct imc_events *events, int nr_entries)
> +{
> +	int i;
> +
> +	/* Nothing to clean, return */
> +	if (!events)
> +		return;
> +	for (i = 0; i < nr_entries; i++) {
> +		kfree(events[i].ev_name);
> +		kfree(events[i].ev_value);
> +	}
> +
> +	kfree(events);
> +}
> +
> +/*
> + * imc_pmu_create : Takes the parent device which is the pmu unit and a
> + *                  pmu_index as the inputs.
> + * Allocates memory for the pmu, sets up its domain (NEST or CORE), and

> + * allocates memory for the events supported by this pmu. Assigns a name for
> + * the pmu. Calls imc_events_node_parser() to setup the individual events.
> + * If everything goes fine, it calls, init_imc_pmu() to setup the pmu device
> + * and register it.
> + */
> +static int imc_pmu_create(struct device_node *parent, int pmu_index)
> +{
> +	struct device_node *ev_node = NULL, *dir = NULL;
> +	struct imc_events *events;
> +	struct imc_pmu *pmu_ptr;
> +	u32 prop, reg;
> +	struct property *pp, *scale_pp, *unit_pp, *name_prefix;
> +	char *buf;
> +	int idx = 0, ret = 0, nr_children = 0;
> +
> +	if (!parent)
> +		return -EINVAL;
> +
> +	/* memory for pmu */
> +	pmu_ptr = kzalloc(sizeof(struct imc_pmu), GFP_KERNEL);
> +	if (!pmu_ptr)
> +		return -ENOMEM;
> +
> +	pmu_ptr->domain = imc_get_domain(parent);
> +	if (pmu_ptr->domain == IMC_DOMAIN_UNKNOWN)
> +		goto free_pmu;
> +
> +	/* Needed for hotplug/migration */
> +	per_nest_pmu_arr[pmu_index] = pmu_ptr;
> +
> +	/*
> +	 * "events" property inside a PMU node contains the phandle value
> +	 * for the actual events node. The "events" node for the IMC PMU
> +	 * is not in this node, rather inside "imc-counters" node, since,
> +	 * we want to factor out the common events (thereby, reducing the
> +	 * size of the device tree)
> +	 */
> +	of_property_read_u32(parent, "events", &prop);
> +	if (!prop)
> +		return -EINVAL;
> +
> +	/*
> +	 * Fetch the actual node where the events for this PMU exist.
> +	 */
> +	dir = of_find_node_by_phandle(prop);
> +	if (!dir)
> +		return -EINVAL;
> +
> +	/*
> +	 * Get the maximum no. of events in this node.
> +	 * Multiply by 3 to account for .scale and .unit properties
> +	 * This number suggests the amount of memory needed to setup the
> +	 * events for this pmu.
> +	 */
> +	nr_children = get_nr_children(dir) * 3;
> +
> +	/* memory for pmu events */
> +	events = kzalloc((sizeof(struct imc_events) * nr_children),
> +			 GFP_KERNEL);
> +	if (!events) {
> +		ret = -ENOMEM;
> +		goto free_pmu;
> +	}
> +
> +	pp = of_find_property(parent, "name", NULL);
> +	if (!pp) {
> +		ret = -ENODEV;
> +		goto free_events;
> +	}
> +
> +	if (!pp->value ||
> +	  (strnlen(pp->value, pp->length) == pp->length) ||
> +	    (pp->length > IMC_MAX_PMU_NAME_LEN)) {
> +		ret = -EINVAL;
> +		goto free_events;
> +	}
> +
> +	buf = kzalloc(IMC_MAX_PMU_NAME_LEN, GFP_KERNEL);
> +	if (!buf) {
> +		ret = -ENOMEM;
> +		goto free_events;
> +	}
> +
> +	/* Save the name to register it later */
> +	sprintf(buf, "nest_%s", (char *)pp->value);
> +	pmu_ptr->pmu.name = (char *)buf;
> +
> +	/*
> +	 * Check if there is a common "scale" and "unit" properties inside
> +	 * the PMU node for all the events supported by this PMU.
> +	 */
> +	scale_pp = of_find_property(parent, "scale", NULL);
> +	unit_pp = of_find_property(parent, "unit", NULL);
> +
> +	/*
> +	 * Get the event-prefix property from the PMU node
> +	 * which needs to be attached with the event names.
> +	 */
> +	name_prefix = of_find_property(parent, "events-prefix", NULL);
> +	if (!name_prefix)
> +		return -ENODEV;
> +
> +	/*
> +	 * "reg" property gives out the base offset of the counters data
> +	 * for this PMU.
> +	 */
> +	of_property_read_u32(parent, "reg", &reg);
> +
> +	if (!name_prefix->value ||
> +	   (strnlen(name_prefix->value, name_prefix->length) == name_prefix->length) ||
> +	   (name_prefix->length > IMC_MAX_PMU_NAME_LEN))
> +		return -EINVAL;
> +
> +	/* Loop through event nodes */
> +	for_each_child_of_node(dir, ev_node) {
> +		ret = imc_events_node_parser(ev_node, &events[idx], scale_pp,
> +					     unit_pp, name_prefix, reg);
> +		if (ret < 0) {
> +			/* Unable to parse this event */
> +			if (ret == -ENOMEM)
> +				goto free_events;
> +			continue;
> +		}
> +
> +		/*
> +		 * imc_event_node_parser will return number of
> +		 * event entries created for this. This could include
> +		 * event scale and unit files also.
> +		 */
> +		idx += ret;
> +	}
> +
> +	return 0;
> +
> +free_events:
> +	imc_free_events(events, idx);
> +free_pmu:
> +	kfree(pmu_ptr);
> +	return ret;
> +}
> +
> +/*
> + * imc_pmu_setup : Setup the IMC PMUs (children of "parent").
> + */
> +static void imc_pmu_setup(struct device_node *parent)

Should this be marked __init?
> +{
> +	struct device_node *child;
> +	int pmu_count = 0, rc = 0;
> +	const struct property *pp;
> +
> +	if (!parent)
> +		return;
> +
> +	/* Setup all the IMC pmus */
> +	for_each_child_of_node(parent, child) {
> +		pp = of_get_property(child, "compatible", NULL);
> +		if (pp) {
> +			/*
> +			 * If there is a node with a "compatible" field,
> +			 * that's a PMU node
> +			 */
> +			rc = imc_pmu_create(child, pmu_count);
> +			if (rc)
> +				return;
> +			pmu_count++;
> +		}
> +	}
> +}
>  
>  static int opal_imc_counters_probe(struct platform_device *pdev)
>  {
> @@ -102,6 +484,10 @@ static int opal_imc_counters_probe(struct platform_device *pdev)
>  		} while (i < (pcni->size / PAGE_SIZE));
>  	}
>  
> +#ifdef CONFIG_PERF_EVENTS
> +	imc_pmu_setup(imc_dev);
> +#endif
> +
>  	return 0;
>  err:
>  	return -ENODEV;
> -- 
> 2.7.4

Regards,
Daniel

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