Re: [PATCH V7 2/4] drivers/perf: imx_ddr: Add ddr performance counter support

[Mark Rutland <mark.rutland@arm.com>]

Hi Frank,

On Thu, Apr 25, 2019 at 07:19:46PM +0000, Frank Li wrote:
> Add ddr performance monitor support for iMX8QXP
> 
> There are 4 counters for ddr perfomance events.
> counter 0 is dedicated for cycles.
> you choose any up to 3 no cycles events.

This is looking better, but there are a few issues I've spotted (e.g.
with over-allocation) that make me somewhat dubious.

> 
> for example:
> 
> perf stat -a -e ddr0/read-cycles/,ddr0/write-cycles/,ddr0/precharge/ ls
> perf stat -a -e ddr0/cycles/,ddr0/read-access/,ddr0/write-access/ ls
> 
> Support below events.
> 
>   ddr0/activate/                                     [Kernel PMU event]
>   ddr0/axid-read/                                    [Kernel PMU event]
>   ddr0/axid-write/                                   [Kernel PMU event]
>   ddr0/cycles/                                       [Kernel PMU event]
>   ddr0/hp-read-credit-cnt/                           [Kernel PMU event]
>   ddr0/hp-read/                                      [Kernel PMU event]
>   ddr0/hp-req-nodcredit/                             [Kernel PMU event]
>   ddr0/hp-xact-credit/                               [Kernel PMU event]
>   ddr0/load-mode/                                    [Kernel PMU event]
>   ddr0/lp-read-credit-cnt/                           [Kernel PMU event]
>   ddr0/lp-req-nocredit/                              [Kernel PMU event]
>   ddr0/lp-xact-credit/                               [Kernel PMU event]
>   ddr0/mwr/                                          [Kernel PMU event]
>   ddr0/precharge/                                    [Kernel PMU event]
>   ddr0/raw-hazard/                                   [Kernel PMU event]
>   ddr0/read-access/                                  [Kernel PMU event]
>   ddr0/read-activate/                                [Kernel PMU event]
>   ddr0/read-command/                                 [Kernel PMU event]
>   ddr0/read-cycles/                                  [Kernel PMU event]
>   ddr0/read-modify-write-command/                    [Kernel PMU event]
>   ddr0/read-queue-depth/                             [Kernel PMU event]
>   ddr0/read-write-transition/                        [Kernel PMU event]
>   ddr0/read/                                         [Kernel PMU event]
>   ddr0/refresh/                                      [Kernel PMU event]
>   ddr0/selfresh/                                     [Kernel PMU event]
>   ddr0/wr-xact-credit/                               [Kernel PMU event]
>   ddr0/write-access/                                 [Kernel PMU event]
>   ddr0/write-command/                                [Kernel PMU event]
>   ddr0/write-credit-cnt/                             [Kernel PMU event]
>   ddr0/write-cycles/                                 [Kernel PMU event]
>   ddr0/write-queue-depth/                            [Kernel PMU event]
>   ddr0/write/
> 
> Signed-off-by: Frank Li <Frank.Li@nxp.com>
> ---
> Change from v6 to v7
>  * added irq affinity handle, ref arm-ccn.c
>  * added IRQF_NOBALANCING | IRQF_NO_THREAD
>  * added ida_simple_remove at failure path
> 
> Change from v5 to v6
>  * fix insmod\rmmod problem
>  * remove randunt register read at irq handle
>  * change u32 irq to int
>  * devm_request_irq use default flags.
> 
> Change from v4 to v5
>  * Remove AXI ID filter function
> 
> Change from v3 to v4
>  * Change FSL_IMX8_DDR_PERF to FSL_IMX8_DDR_PMU
>  * sort include
>  * remove struct fsl_ddr_devtype_data
>  * Added comment need disable control first
>  * Added comment about must enable cycle counter
>  * Added macro for EVENT_AXI_READ, remove hardcode 0x41 and 0x42
>  * Added comment about cycle counter is fastest one
> 
> Change from v2 to v3
>  * remove kfree
> 
> Change from V1 to V2
>  * update Kconfig by use i.MX8 instead of i.MX8 QXP
>  * remove gpl statememnt since SPDX tag
>  * use dev_kzalloc
>  * use dev_err
>  * commit message show axi_read 0x41\axi_write 0x42
>  * commit message show cycles must be enabled
>  * Irq only issue at cycles overflow
>  * use NUM_COUNTER
>  * use devm_request_irq
>  * add hotplug callback to handle context migration
> 
>  drivers/perf/Kconfig             |   7 +
>  drivers/perf/Makefile            |   1 +
>  drivers/perf/fsl_imx8_ddr_perf.c | 562 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 570 insertions(+)
>  create mode 100644 drivers/perf/fsl_imx8_ddr_perf.c
> 
> diff --git a/drivers/perf/Kconfig b/drivers/perf/Kconfig
> index a94e586..9bc3785 100644
> --- a/drivers/perf/Kconfig
> +++ b/drivers/perf/Kconfig
> @@ -70,6 +70,13 @@ config ARM_DSU_PMU
>  	  system, control logic. The PMU allows counting various events related
>  	  to DSU.
>  
> +config FSL_IMX8_DDR_PMU
> +	tristate "Freescale i.MX8 DDR perf monitor"
> +	depends on ARCH_MXC
> +	  help
> +	  Provides support for ddr perfomance monitor in i.MX8. Provide memory
> +	  througput information.
> +
>  config HISI_PMU
>         bool "HiSilicon SoC PMU"
>         depends on ARM64 && ACPI
> diff --git a/drivers/perf/Makefile b/drivers/perf/Makefile
> index 3048994..2ebb4de 100644
> --- a/drivers/perf/Makefile
> +++ b/drivers/perf/Makefile
> @@ -5,6 +5,7 @@ obj-$(CONFIG_ARM_DSU_PMU) += arm_dsu_pmu.o
>  obj-$(CONFIG_ARM_PMU) += arm_pmu.o arm_pmu_platform.o
>  obj-$(CONFIG_ARM_PMU_ACPI) += arm_pmu_acpi.o
>  obj-$(CONFIG_ARM_SMMU_V3_PMU) += arm_smmuv3_pmu.o
> +obj-$(CONFIG_FSL_IMX8_DDR_PMU) += fsl_imx8_ddr_perf.o
>  obj-$(CONFIG_HISI_PMU) += hisilicon/
>  obj-$(CONFIG_QCOM_L2_PMU)	+= qcom_l2_pmu.o
>  obj-$(CONFIG_QCOM_L3_PMU) += qcom_l3_pmu.o
> diff --git a/drivers/perf/fsl_imx8_ddr_perf.c b/drivers/perf/fsl_imx8_ddr_perf.c
> new file mode 100644
> index 0000000..7286182
> --- /dev/null
> +++ b/drivers/perf/fsl_imx8_ddr_perf.c
> @@ -0,0 +1,562 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright 2017 NXP
> + * Copyright 2016 Freescale Semiconductor, Inc.
> + */
> +
> +#include <linux/init.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> +#include <linux/of_device.h>
> +#include <linux/of_irq.h>
> +#include <linux/perf_event.h>
> +#include <linux/slab.h>
> +
> +#define COUNTER_CNTL		0x0
> +#define COUNTER_READ		0x20
> +
> +#define COUNTER_DPCR1		0x30
> +
> +#define CNTL_OVER		0x1
> +#define CNTL_CLEAR		0x2
> +#define CNTL_EN			0x4
> +#define CNTL_EN_MASK		0xFFFFFFFB
> +#define CNTL_CLEAR_MASK		0xFFFFFFFD
> +#define CNTL_OVER_MASK		0xFFFFFFFE
> +
> +#define CNTL_CSV_SHIFT		24
> +#define CNTL_CSV_MASK		(0xFF << CNTL_CSV_SHIFT)
> +
> +#define EVENT_CYCLES_ID		0
> +#define EVENT_CYCLES_COUNTER	0
> +#define NUM_COUNTER		4

Nit: this should be NUM_COUNTERS

> +#define MAX_EVENT		3
> +#define EVENT_AXI_READ		0x41
> +#define EVENT_AXI_WRITE		0x42

These three definitions aren't used, so we can drop them for now.

> +
> +#define to_ddr_pmu(p)		container_of(p, struct ddr_pmu, pmu)
> +
> +#define DDR_PERF_DEV_NAME	"ddr_perf"
> +
> +static DEFINE_IDA(ddr_ida);
> +
> +PMU_EVENT_ATTR_STRING(cycles, ddr_perf_cycles, "event=0x00");
> +PMU_EVENT_ATTR_STRING(selfresh, ddr_perf_selfresh, "event=0x01");
> +PMU_EVENT_ATTR_STRING(read-access, ddr_perf_read_accesses, "event=0x04");
> +PMU_EVENT_ATTR_STRING(write-access, ddr_perf_write_accesses, "event=0x05");
> +PMU_EVENT_ATTR_STRING(read-queue-depth, ddr_perf_read_queue_depth,
> +			"event=0x08");
> +PMU_EVENT_ATTR_STRING(write-queue-depth, ddr_perf_write_queue_depth,
> +			"event=0x09");
> +PMU_EVENT_ATTR_STRING(lp-read-credit-cnt, ddr_perf_lp_read_credit_cnt,
> +			"event=0x10");
> +PMU_EVENT_ATTR_STRING(hp-read-credit-cnt, ddr_perf_hp_read_credit_cnt,
> +			"event=0x11");
> +PMU_EVENT_ATTR_STRING(write-credit-cnt, ddr_perf_write_credit_cnt,
> +			"event=0x12");
> +PMU_EVENT_ATTR_STRING(read-command, ddr_perf_read_command, "event=0x20");
> +PMU_EVENT_ATTR_STRING(write-command, ddr_perf_write_command, "event=0x21");
> +PMU_EVENT_ATTR_STRING(read-modify-write-command,
> +		ddr_perf_read_modify_write_command, "event=0x22");
> +PMU_EVENT_ATTR_STRING(hp-read, ddr_perf_hp_read, "event=0x23");
> +PMU_EVENT_ATTR_STRING(hp-req-nodcredit, ddr_perf_hp_req_nocredit, "event=0x24");
> +PMU_EVENT_ATTR_STRING(hp-xact-credit, ddr_perf_hp_xact_credit, "event=0x25");
> +PMU_EVENT_ATTR_STRING(lp-req-nocredit, ddr_perf_lp_req_nocredit, "event=0x26");
> +PMU_EVENT_ATTR_STRING(lp-xact-credit, ddr_perf_lp_xact_credit, "event=0x27");
> +PMU_EVENT_ATTR_STRING(wr-xact-credit, ddr_perf_wr_xact_credit, "event=0x29");
> +PMU_EVENT_ATTR_STRING(read-cycles, ddr_perf_read_cycles, "event=0x2a");
> +PMU_EVENT_ATTR_STRING(write-cycles, ddr_perf_write_cycles, "event=0x2b");
> +PMU_EVENT_ATTR_STRING(read-write-transition, ddr_perf_read_write_transition,
> +			"event=0x30");
> +PMU_EVENT_ATTR_STRING(precharge, ddr_perf_precharge, "event=0x31");
> +PMU_EVENT_ATTR_STRING(activate, ddr_perf_activate, "event=0x32");
> +PMU_EVENT_ATTR_STRING(load-mode, ddr_perf_load_mode, "event=0x33");
> +PMU_EVENT_ATTR_STRING(mwr, ddr_perf_mwr, "event=0x34");
> +PMU_EVENT_ATTR_STRING(read, ddr_perf_read, "event=0x35");
> +PMU_EVENT_ATTR_STRING(read-activate, ddr_perf_read_activate, "event=0x36");
> +PMU_EVENT_ATTR_STRING(refresh, ddr_perf_refresh, "event=0x37");
> +PMU_EVENT_ATTR_STRING(write, ddr_perf_write, "event=0x38");
> +PMU_EVENT_ATTR_STRING(raw-hazard, ddr_perf_raw_hazard, "event=0x39");
> +
> +static const struct of_device_id imx_ddr_pmu_dt_ids[] = {
> +	{ .compatible = "fsl,imx8-ddr-pmu",},
> +	{ .compatible = "fsl,imx8m-ddr-pmu",},
> +	{ /* sentinel */ }
> +};
> +
> +struct ddr_pmu {
> +	struct pmu pmu;
> +	void __iomem *base;
> +	unsigned int cpu;
> +	struct	hlist_node node;
> +	struct	device *dev;
> +	struct perf_event *active_events[NUM_COUNTER];
> +	int total_events;

Can we please make these two:

	struct perf_event *events[NUM_COUNTERS];
	int active_events;

... which would be more consistent with other drivers.

> +	enum cpuhp_state cpuhp_state;
> +	bool cycles_active;
> +	uintptr_t flags;

AFAICT this flags field isn't used at runtime, and can be dropped for
now.

> +	int irq;
> +	int id;
> +};

[...]

> +static u32 ddr_perf_alloc_counter(struct ddr_pmu *pmu, int event)
> +{
> +	int i;
> +
> +	/* Always map cycle event to counter 0
> +	   Cycles counter is dedicated for cycle event
> +	   can't used for the other events
> +	 */

Please follow the coding style, as documented in
Documentation/process/coding-style.rst.

Multi line comments look like:

	/*
	 * Nothing on the first line, with an asterisk on each
	 * successive line.
	 */

> +	if (event == EVENT_CYCLES_ID)
> +		return EVENT_CYCLES_COUNTER;

I don't think this is safe as-is. If a user tries to open multiple
cycles events, ddr_perf_event_add() will overwrite the existing event
pointer, and the IRQ handler won't update the event.

You'll at least need to check whether you already have a cycles event
here.

> +
> +	for (i = 1; i < NUM_COUNTER; i++)
> +		if (pmu->active_events[i] == NULL)
> +			return i;

Nit: this should have braces around the body of the for-loop.

> +
> +	return -ENOENT;
> +}
> +
> +static u32 ddr_perf_free_counter(struct ddr_pmu *pmu, int counter)
> +{
> +	if (counter < 0 || counter >= NUM_COUNTER)
> +		return -ENOENT;

AFAICT, this should never happen, and the return value is never used, so
this can go.

> +
> +	pmu->active_events[counter] = NULL;
> +
> +	return 0;
> +}
> +
> +static u32 ddr_perf_read_counter(struct ddr_pmu *pmu, int counter)
> +{
> +	return readl(pmu->base + COUNTER_READ + counter * 4);
> +}
> +
> +static int ddr_perf_event_init(struct perf_event *event)
> +{
> +	struct ddr_pmu *pmu = to_ddr_pmu(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +
> +	if (event->attr.type != event->pmu->type)
> +		return -ENOENT;
> +
> +	if (is_sampling_event(event) || event->attach_state & PERF_ATTACH_TASK)
> +		return -EOPNOTSUPP;
> +
> +	if (event->cpu < 0) {
> +		dev_warn(pmu->dev, "Can't provide per-task data!\n");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	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       ||
> +	    event->attr.sample_period)
> +		return -EINVAL;
> +
> +	event->cpu = pmu->cpu;
> +	hwc->idx = -1;
> +
> +	return 0;
> +}

This should have a check for event grouping, e.g. like that in
arm_ccn_pmu_event_init.

> +
> +
> +static void ddr_perf_event_update(struct perf_event *event)
> +{
> +	struct ddr_pmu *pmu = to_ddr_pmu(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +	u64 delta, prev_raw_count, new_raw_count;
> +	int counter = hwc->idx;
> +
> +	do {
> +		prev_raw_count = local64_read(&hwc->prev_count);
> +		new_raw_count = ddr_perf_read_counter(pmu, counter);
> +	} while (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
> +			new_raw_count) != prev_raw_count);
> +
> +	delta = (new_raw_count - prev_raw_count) & 0xFFFFFFFF;
> +
> +	local64_add(delta, &event->count);
> +}
> +
> +static void ddr_perf_event_enable(struct ddr_pmu *pmu, int config,
> +				  int counter, bool enable)
> +{
> +	u8 reg = counter * 4 + COUNTER_CNTL;
> +	int val;
> +
> +	if (enable) {
> +		/* must disable first, then enable again
> +		 * otherwise, cycle counter will not work
> +		 * if previous state is enabled.
> +		 */

Nit: comment style violation.

> +		writel(0, pmu->base + reg);
> +		val = CNTL_EN | CNTL_CLEAR;
> +		val |= (config << CNTL_CSV_SHIFT) & CNTL_CSV_MASK;

Do you need to do this for all counters, or is this only necessary when
programming the cycle counter itself?

> +	} else {
> +		/* Disable counter */
> +		val = readl(pmu->base + reg) & CNTL_EN_MASK;
> +	}
> +
> +	writel(val, pmu->base + reg);
> +
> +	if (config == EVENT_CYCLES_ID)
> +		pmu->cycles_active = enable;
> +}

Rather than keeping track of whether you have a cycles event, I think it
would be better to use the cycles enable/disable to implement
pmu::pmu_{enable,disable}(), and in the pmu::start() callback, bail out
for a cycles event.

In the pmu::pmu_enable() callback, you can look at how many events you
have in order to decide whether to enable the cycle counter or leave it
disabled.

That way, you'll always program it when you need to, you don't need to
special-case the programming of a cycles event as much, and you don't
need to check the number of active events as much.

> +static void ddr_perf_event_start(struct perf_event *event, int flags)
> +{
> +	struct ddr_pmu *pmu = to_ddr_pmu(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +	int counter = hwc->idx;
> +
> +	local64_set(&hwc->prev_count, 0);
> +
> +	ddr_perf_event_enable(pmu, event->attr.config, counter, true);
> +	/*
> +	 * If the cycles counter wasn't explicitly selected,
> +	 * we will enable it now.
> +	 * cycles counter must be enabled otherwise other counters will
> +	 * stopped.
> +	 */
> +	if (counter > 0 && !pmu->cycles_active)
> +		ddr_perf_event_enable(pmu, EVENT_CYCLES_ID,
> +				      EVENT_CYCLES_COUNTER, true);
> +}
> +
> +static int ddr_perf_event_add(struct perf_event *event, int flags)
> +{
> +	struct ddr_pmu *pmu = to_ddr_pmu(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +	int counter;
> +	int cfg = event->attr.config;
> +
> +	counter = ddr_perf_alloc_counter(pmu, cfg);
> +	if (counter < 0) {
> +		dev_dbg(pmu->dev, "There are not enough counters\n");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	pmu->active_events[counter] = event;
> +	pmu->total_events++;
> +	hwc->idx = counter;
> +
> +	if (flags & PERF_EF_START)
> +		ddr_perf_event_start(event, flags);
> +
> +	local64_set(&hwc->prev_count, ddr_perf_read_counter(pmu, counter));
> +
> +	return 0;
> +}
> +
> +static void ddr_perf_event_stop(struct perf_event *event, int flags)
> +{
> +	struct ddr_pmu *pmu = to_ddr_pmu(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +	int counter = hwc->idx;
> +
> +	ddr_perf_event_enable(pmu, event->attr.config, counter, false);
> +	ddr_perf_event_update(event);
> +}
> +
> +static void ddr_perf_event_del(struct perf_event *event, int flags)
> +{
> +	struct ddr_pmu *pmu = to_ddr_pmu(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +	int counter = hwc->idx;
> +
> +	ddr_perf_event_stop(event, PERF_EF_UPDATE);
> +
> +	ddr_perf_free_counter(pmu, counter);
> +	pmu->total_events--;
> +	hwc->idx = -1;
> +
> +	/* If all events have stopped, stop the cycles counter as well */
> +	if ((pmu->total_events == 0) && pmu->cycles_active)
> +		ddr_perf_event_enable(pmu, EVENT_CYCLES_ID,
> +				      EVENT_CYCLES_COUNTER, false);
> +}
> +
> +static int ddr_perf_init(struct ddr_pmu *pmu, void __iomem *base,
> +			 struct device *dev)
> +{
> +	*pmu = (struct ddr_pmu) {
> +		.pmu = (struct pmu) {
> +			.task_ctx_nr = perf_invalid_context,
> +			.attr_groups = attr_groups,
> +			.event_init  = ddr_perf_event_init,
> +			.add	     = ddr_perf_event_add,
> +			.del	     = ddr_perf_event_del,
> +			.start	     = ddr_perf_event_start,
> +			.stop	     = ddr_perf_event_stop,
> +			.read	     = ddr_perf_event_update,
> +		},
> +		.base = base,
> +		.dev = dev,
> +	};
> +
> +	pmu->id = ida_simple_get(&ddr_ida, 0, 0, GFP_KERNEL);
> +	return pmu->id;
> +}
> +
> +static irqreturn_t ddr_perf_irq_handler(int irq, void *p)
> +{
> +	int i;
> +	struct ddr_pmu *pmu = (struct ddr_pmu *) p;
> +	struct perf_event *event;
> +
> +	/* Only cycles counter overflowed can issue irq. all counters will
> +	 * be stopped when cycles counter overflow. but other counter don't stop
> +	 * when overflow happen. Update all of the local counter values,
> +	 * then reset the cycles counter, so the others can continue
> +	 * counting. cycles counter is fastest counter in all events. at last
> +	 * 4 times than other counters.
> +	 */

Let's make this:

	/*
	 * When the cycle counter overflows, all counters are stopped,
	 * and an IRQ is raised. If any other counter overflows, it
	 * continues counting, and no IRQ is raised.
	 *
	 * Cycles occur at least 4 times as often as other events, so we
	 * can update all events on a cycle counter overflow and not
	 * lose events.
	 */

> +	for (i = 0; i < NUM_COUNTER; i++) {
> +
> +		if (!pmu->active_events[i])
> +			continue;
> +
> +		event = pmu->active_events[i];
> +
> +		ddr_perf_event_update(event);
> +
> +		if (event->hw.idx == EVENT_CYCLES_COUNTER) {
> +			ddr_perf_event_enable(pmu,
> +					      EVENT_CYCLES_ID,
> +					      EVENT_CYCLES_COUNTER,
> +					      true);
> +			ddr_perf_event_update(event);
> +		}
> +	}

This allows events to be counting during the IRQ handler, and will lead
to skid within event groups. I think that we should disable the cycle
counter before the loop, and enable it afterwards in order to avoid
that.

If you implement pmu_{enable,disable}() as suggested above, you can use
those here.

> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int ddr_perf_offline_cpu(unsigned int cpu, struct hlist_node *node)
> +{
> +	struct ddr_pmu *pmu = hlist_entry_safe(node, struct ddr_pmu, node);
> +	int target;
> +
> +	if (cpu != pmu->cpu)
> +		return 0;
> +
> +	target = cpumask_any_but(cpu_online_mask, cpu);
> +	if (target >= nr_cpu_ids)
> +		return 0;
> +
> +	perf_pmu_migrate_context(&pmu->pmu, cpu, target);
> +	pmu->cpu = target;
> +
> +	if (pmu->irq)

In ddr_perf_probe() we'll bail out if we didn't have an IRQ, so you
don't need to check that pmu->irq has been set here.

> +		WARN_ON(irq_set_affinity_hint(pmu->irq, cpumask_of(pmu->cpu)));
> +
> +	return 0;
> +}
> +
> +static int ddr_perf_probe(struct platform_device *pdev)
> +{
> +	struct ddr_pmu *pmu;
> +	struct device_node *np;
> +	void __iomem *base;
> +	struct resource *iomem;
> +	char *name;
> +	char *hpname;
> +	int num;
> +	int ret;
> +	int irq;
> +	const struct of_device_id *of_id =
> +		of_match_device(imx_ddr_pmu_dt_ids, &pdev->dev);
> +
> +	iomem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	base = devm_ioremap_resource(&pdev->dev, iomem);
> +	if (IS_ERR(base))
> +		return PTR_ERR(base);
> +
> +	np = pdev->dev.of_node;
> +
> +	pmu = devm_kzalloc(&pdev->dev, sizeof(*pmu), GFP_KERNEL);
> +	if (!pmu)
> +		return -ENOMEM;
> +
> +	num = ddr_perf_init(pmu, base, &pdev->dev);
> +
> +	platform_set_drvdata(pdev, pmu);
> +
> +	name = devm_kasprintf(&pdev->dev, GFP_KERNEL, "ddr%d", num);
> +	if (!name)
> +		return -ENOMEM;
> +
> +	hpname = devm_kasprintf(&pdev->dev, GFP_KERNEL,
> +				"perf/imx/ddr%d:online", num);
> +	if (!hpname)
> +		return -ENOMEM;
> +
> +	pmu->flags = (uintptr_t) of_id->data;

As above, I think this can go for now.

> +
> +	pmu->cpu = raw_smp_processor_id();
> +	ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, hpname, NULL,
> +					 ddr_perf_offline_cpu);
> +
> +	if (ret < 0) {
> +		dev_err(&pdev->dev, "cpuhp_setup_state_multi failed\n");
> +		goto ddr_perf_err;
> +	}
> +
> +	pmu->cpuhp_state = ret;
> +
> +	/* Register the pmu instance for cpu hotplug */
> +	cpuhp_state_add_instance_nocalls(pmu->cpuhp_state, &pmu->node);
> +
> +	ret = perf_pmu_register(&(pmu->pmu), name, -1);

Here, "&(pmu->pmu)" can be "&pmu->pmu", no backets required.

Thanks,
Mark.