[PATCH 0/2] perf: Support Arm Bus Monitor Unit

[PATCH 0/2] perf: Support Arm Bus Monitor Unit

[Robin Murphy]

Hi all,

Here we have the delight of another new PMU driver. While not am Arm
product in its own right, the BMU is found in the latest Neoverse
Compute Subsystems, including the recently-announced AGI CPU.

For now it is expected that BMU users will be ACPI-based (binding in
the latest "ACPI for Arm Components" release[1]), so the token DT
binding is more for completeness and maybe very early bringup hacking,
but there is a chance it may end up being used by more embedded/client-
focused subsystems in future.

And yes, I did initially look at trying to factor out the PMU register
accesses that functionally overlap the existing arm_cspmu code, but it
very quickly became clear that that would end up far bigger and more
complex. This is not a big driver, even with a few dozen lines of
nominally-duplicate (but also simplified since the counter size etc.
is fixed and known) code, so this way it went.

Thanks,
Robin.

[1] https://developer.arm.com/documentation/den0093/latest/


Robin Murphy (2):
  dt-bindings: perf: Add Arm Bus Monitor Unit
  perf: Add Arm Bus Monitor Unit driver

 .../bindings/perf/arm,bus-monitor-unit.yaml   |  33 ++
 drivers/perf/arm_cspmu/Kconfig                |   6 +
 drivers/perf/arm_cspmu/Makefile               |   2 +
 drivers/perf/arm_cspmu/arm-bmu.c              | 538 ++++++++++++++++++
 4 files changed, 579 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/perf/arm,bus-monitor-unit.yaml
 create mode 100644 drivers/perf/arm_cspmu/arm-bmu.c

-- 
2.54.0.dirty

[PATCH 1/2] dt-bindings: perf: Add Arm Bus Monitor Unit

[Robin Murphy]

Arm's Bus Monitor Unit is a low-level performance analysis tool for
matching and counting transactions at interconnect interfaces. Typical
platforms will have multiple BMUs each measuring multiple interfaces in
various parts of the system, hence for the sake of usability we make it
mandatory for the platform to label each instance such that the end user
can correlate with platform documentation to know what's what.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 .../bindings/perf/arm,bus-monitor-unit.yaml   | 33 +++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/perf/arm,bus-monitor-unit.yaml

diff --git a/Documentation/devicetree/bindings/perf/arm,bus-monitor-unit.yaml b/Documentation/devicetree/bindings/perf/arm,bus-monitor-unit.yaml
new file mode 100644
index 000000000000..3cdc3a05b9a6
--- /dev/null
+++ b/Documentation/devicetree/bindings/perf/arm,bus-monitor-unit.yaml
@@ -0,0 +1,33 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/perf/arm,bus-monitor-unit.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Arm Bus Monitor Unit
+
+maintainers:
+  - Robin Murphy <robin.murphy@arm.com>
+
+properties:
+  compatible:
+    const: arm,bus-monitor-unit
+
+  reg:
+    items:
+      - description: Full BMU register space
+
+  interrupts:
+    items:
+      - description: PMU overflow interrupt
+
+  label:
+    description: BMU instance identifier (same as ACPI _UID), per the
+      platform optimisation guide
+
+required:
+  - compatible
+  - reg
+  - label
+
+additionalProperties: false
-- 
2.54.0.dirty

[PATCH 2/2] perf: Add Arm Bus Monitor Unit driver

[Robin Murphy]

Arm's Bus Monitor Unit is a low-level performance analysis tool for
matching and counting transactions at interconnect interfaces. Each
BMU consists of a number of "interface monitoring units", with some
global controls to synchronise them and so permit accurate calculation
of cross-interface metrics. Each IMU contains, among other things, its
own PMU largely based on the CoreSight PMU architecture, but with some
functional incompatibilities due to the nature of how much per-event
filtering needs to be crammed in to categorise AXI/CHI transactions at
the protocol level. As such it gets an honorary home in arm_cspmu/ in
order to share the common register definitions, but for simplicity does
not try to bend the functional abstraction to fit.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/perf/arm_cspmu/Kconfig   |   6 +
 drivers/perf/arm_cspmu/Makefile  |   2 +
 drivers/perf/arm_cspmu/arm-bmu.c | 538 +++++++++++++++++++++++++++++++
 3 files changed, 546 insertions(+)
 create mode 100644 drivers/perf/arm_cspmu/arm-bmu.c

diff --git a/drivers/perf/arm_cspmu/Kconfig b/drivers/perf/arm_cspmu/Kconfig
index 6f4e28fc84a2..8a7e2082b850 100644
--- a/drivers/perf/arm_cspmu/Kconfig
+++ b/drivers/perf/arm_cspmu/Kconfig
@@ -27,3 +27,9 @@ config AMPERE_CORESIGHT_PMU_ARCH_SYSTEM_PMU
 
 	  In the first phase, the driver enables support on MCU PMU used in
 	  AmpereOne SoC family.
+
+config ARM_BMU
+	tristate "ARM Bus Monitor Unit"
+	depends on ARM64 || COMPILE_TEST
+	help
+	  Support perf event counting on Arm Bus Monitor Unit devices.
diff --git a/drivers/perf/arm_cspmu/Makefile b/drivers/perf/arm_cspmu/Makefile
index 220a734efd54..622b8fc3d5dc 100644
--- a/drivers/perf/arm_cspmu/Makefile
+++ b/drivers/perf/arm_cspmu/Makefile
@@ -8,3 +8,5 @@ arm_cspmu_module-y := arm_cspmu.o
 
 obj-$(CONFIG_NVIDIA_CORESIGHT_PMU_ARCH_SYSTEM_PMU) += nvidia_cspmu.o
 obj-$(CONFIG_AMPERE_CORESIGHT_PMU_ARCH_SYSTEM_PMU) += ampere_cspmu.o
+
+obj-$(CONFIG_ARM_BMU) += arm-bmu.o
diff --git a/drivers/perf/arm_cspmu/arm-bmu.c b/drivers/perf/arm_cspmu/arm-bmu.c
new file mode 100644
index 000000000000..0ed9e34857ff
--- /dev/null
+++ b/drivers/perf/arm_cspmu/arm-bmu.c
@@ -0,0 +1,538 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2025-2026 Arm Limited
+
+#include <linux/acpi.h>
+#include <linux/bitfield.h>
+#include <linux/interrupt.h>
+#include <linux/io-64-nonatomic-lo-hi.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/perf_event.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+
+#include "arm_cspmu.h"
+
+#define MCU_CONFIG			0x0000
+#define MCU_PMU_GLOBAL_EN		0x0008
+#define MCU_PMU_INTERRUPT_STATUS	0x0090
+
+#define MCUCFG_NUM_IMU_MONITORS		GENMASK_ULL(63, 60)
+#define MCUCFG_PMU_ELEMENT_SIZE		GENMASK_ULL(11, 8)
+#define MCUCFG_PMU_ELEMENT_START	GENMASK_ULL(7, 0)
+
+#define BMU_PMIMPDEF			0x0200
+#define BMU_PMCR			0x0e10
+
+/* These are reasonable expectations for now */
+#define PMU_MAX_COUNTERS	16
+#define MAX_IMUS		16
+
+/* Event attributes */
+#define BMU_CONFIG_IMU		GENMASK_ULL(63, 56)
+#define BMU_CONFIG_EVENT	GENMASK_ULL(55, 0)
+#define BMU_CONFIG_FILTER	GENMASK_ULL(63, 0)
+#define BMU_CONFIG_MATCH	GENMASK_ULL(63, 0)
+#define BMU_CONFIG_MASK		GENMASK_ULL(63, 0)
+
+#define BMU_EVENT_IMU(e)	FIELD_GET(BMU_CONFIG_IMU, (e)->attr.config)
+#define BMU_EVENT_EVENT(e)	FIELD_GET(BMU_CONFIG_EVENT, (e)->attr.config)
+#define BMU_EVENT_FILTER(e)	FIELD_GET(BMU_CONFIG_FILTER, (e)->attr.config1)
+#define BMU_EVENT_MATCH(e)	FIELD_GET(BMU_CONFIG_MATCH, (e)->attr.config2)
+#define BMU_EVENT_MASK(e)	FIELD_GET(BMU_CONFIG_MASK, (e)->attr.config3)
+
+static unsigned long arm_bmu_cpuhp_state;
+
+struct arm_bmu_pmu {
+	void __iomem *base;
+	struct perf_event *evcnt[PMU_MAX_COUNTERS];
+	int num_counters;
+};
+
+struct arm_bmu {
+	struct device *dev;
+	void __iomem *base;
+	struct pmu pmu;
+	struct hlist_node cpuhp_node;
+	int cpu;
+	int irq;
+	int num_imus;
+	struct arm_bmu_pmu imus[] __counted_by(num_imus);
+};
+
+#define to_bmu(p)	container_of(p, struct arm_bmu, pmu)
+#define event_imu(e)	(e)->hw.event_base
+#define to_bmu_pmu(e)	&to_bmu(e->pmu)->imus[event_imu(e)]
+
+struct arm_bmu_format_attr {
+	struct device_attribute attr;
+	u64 field;
+	int config;
+};
+
+#define BMU_FORMAT_ATTR(_name, _cfg, _fld)				\
+	(&((struct arm_bmu_format_attr[]) {{				\
+		.attr = __ATTR(_name, 0444, arm_bmu_format_show, NULL),	\
+		.field = _fld,						\
+		.config = _cfg,						\
+	}})[0].attr.attr)
+
+static ssize_t arm_bmu_format_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct arm_bmu_format_attr *fmt = container_of(attr, typeof(*fmt), attr);
+
+	if (!fmt->config)
+		return sysfs_emit(buf, "config:%*pbl\n", 64, &fmt->field);
+
+	return sysfs_emit(buf, "config%d:%*pbl\n", fmt->config, 64, &fmt->field);
+}
+
+static struct attribute *arm_bmu_format_attrs[] = {
+	BMU_FORMAT_ATTR(imu, 0, BMU_CONFIG_IMU),
+	BMU_FORMAT_ATTR(event, 0, BMU_CONFIG_EVENT),
+	BMU_FORMAT_ATTR(filter, 1, BMU_CONFIG_FILTER),
+	BMU_FORMAT_ATTR(match, 2, BMU_CONFIG_MATCH),
+	BMU_FORMAT_ATTR(mask, 3, BMU_CONFIG_MASK),
+	NULL
+};
+
+static const struct attribute_group arm_bmu_format_attrs_group = {
+	.name = "format",
+	.attrs = arm_bmu_format_attrs,
+};
+
+static ssize_t arm_bmu_cpumask_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct arm_bmu *bmu = to_bmu(dev_get_drvdata(dev));
+
+	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpumask_of(bmu->cpu)));
+}
+
+static struct device_attribute arm_bmu_cpumask_attr =
+		__ATTR(cpumask, 0444, arm_bmu_cpumask_show, NULL);
+
+static ssize_t arm_bmu_identifier_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	struct arm_bmu *bmu = to_bmu(dev_get_drvdata(dev));
+	u32 reg = readl_relaxed(bmu->imus[0].base + PMIIDR);
+
+	return sysfs_emit(buf, "%x\n", reg);
+}
+
+static struct device_attribute arm_bmu_identifier_attr =
+		__ATTR(identifier, 0444, arm_bmu_identifier_show, NULL);
+
+static struct attribute *arm_bmu_other_attrs[] = {
+	&arm_bmu_cpumask_attr.attr,
+	&arm_bmu_identifier_attr.attr,
+	NULL
+};
+
+static const struct attribute_group arm_bmu_other_attr_group = {
+	.attrs = arm_bmu_other_attrs,
+};
+
+static const struct attribute_group *arm_bmu_attr_groups[] = {
+	&arm_bmu_format_attrs_group,
+	&arm_bmu_other_attr_group,
+	NULL
+};
+
+static void arm_bmu_enable(struct pmu *pmu)
+{
+	writel_relaxed(1, to_bmu(pmu)->base + MCU_PMU_GLOBAL_EN);
+}
+
+static void arm_bmu_disable(struct pmu *pmu)
+{
+	writel_relaxed(0, to_bmu(pmu)->base + MCU_PMU_GLOBAL_EN);
+}
+
+static int arm_bmu_validate_group(struct perf_event *event)
+{
+	struct arm_bmu *bmu = to_bmu(event->pmu);
+	struct perf_event *sibling, *leader = event->group_leader;
+	int num[MAX_IMUS] = { 0 };
+
+	++num[event_imu(event)];
+	if (leader != event) {
+		if (leader->pmu == &bmu->pmu)
+			++num[event_imu(leader)];
+		for_each_sibling_event(sibling, leader) {
+			if (sibling->pmu == &bmu->pmu)
+				++num[event_imu(sibling)];
+		}
+	}
+	for (int i = 0; i < bmu->num_imus; i++) {
+		if (++num[i] > bmu->imus[i].num_counters)
+			return -EINVAL;
+	}
+	return 0;
+}
+
+static int arm_bmu_event_init(struct perf_event *event)
+{
+	struct arm_bmu *bmu = to_bmu(event->pmu);
+
+	if (event->attr.type != event->pmu->type)
+		return -ENOENT;
+
+	if (is_sampling_event(event))
+		return -EINVAL;
+
+	event->cpu = bmu->cpu;
+	event_imu(event) = BMU_EVENT_IMU(event);
+	if (event_imu(event) >= bmu->num_imus)
+		return -EINVAL;
+
+	return arm_bmu_validate_group(event);
+}
+
+static u64 arm_bmu_read_evcnt(struct perf_event *event)
+{
+	struct arm_bmu_pmu *pmu = to_bmu_pmu(event);
+	void __iomem *reg_base = pmu->base + event->hw.idx * sizeof(u64);
+	u64 lo, hi_old, hi_new;
+	int retries = 3; /* 1st time unlucky, 2nd improbable, 3rd just broken */
+
+	hi_new = readl_relaxed(reg_base + PMEVCNTR_HI);
+	do {
+		hi_old = hi_new;
+		lo = readl_relaxed(reg_base + PMEVCNTR_LO);
+		hi_new = readl_relaxed(reg_base + PMEVCNTR_HI);
+	} while (hi_new != hi_old && --retries);
+	WARN_ON(!retries);
+
+	return (hi_new << 32) | lo;
+}
+
+static void arm_bmu_event_read(struct perf_event *event)
+{
+	struct hw_perf_event *hw = &event->hw;
+	u64 count, prev;
+
+	do {
+		prev = local64_read(&hw->prev_count);
+		count = arm_bmu_read_evcnt(event);
+	} while (local64_cmpxchg(&hw->prev_count, prev, count) != prev);
+
+	count -= prev;
+	local64_add(count, &event->count);
+}
+
+static void arm_bmu_event_start(struct perf_event *event, int flags)
+{
+	struct arm_bmu_pmu *pmu = to_bmu_pmu(event);
+
+	writel_relaxed(1ULL << event->hw.idx, pmu->base + PMCNTENSET);
+}
+
+static void arm_bmu_event_stop(struct perf_event *event, int flags)
+{
+	struct arm_bmu_pmu *pmu = to_bmu_pmu(event);
+
+	writel_relaxed(1ULL << event->hw.idx, pmu->base + PMCNTENCLR);
+	if (flags & PERF_EF_UPDATE)
+		arm_bmu_event_read(event);
+}
+
+static int arm_bmu_event_add(struct perf_event *event, int flags)
+{
+	struct arm_bmu_pmu *pmu = to_bmu_pmu(event);
+	struct hw_perf_event *hw = &event->hw;
+	void __iomem *reg_base;
+
+	hw->idx = 0;
+	while (pmu->evcnt[hw->idx]) {
+		if (++hw->idx == pmu->num_counters)
+			return -ENOSPC;
+	}
+	pmu->evcnt[hw->idx] = event;
+
+	reg_base = pmu->base + hw->idx * sizeof(u64);
+	lo_hi_writeq_relaxed(BMU_EVENT_EVENT(event), reg_base + PMEVTYPER);
+	lo_hi_writeq_relaxed(BMU_EVENT_FILTER(event), reg_base + PMEVFILTR);
+	lo_hi_writeq_relaxed(BMU_EVENT_MATCH(event), reg_base + PMEVFILT2R);
+	lo_hi_writeq_relaxed(BMU_EVENT_MASK(event), reg_base + BMU_PMIMPDEF);
+
+	local64_set(&hw->prev_count, S64_MIN);
+	lo_hi_writeq_relaxed(S64_MIN, reg_base + PMEVCNTR_LO);
+
+	if (flags & PERF_EF_START)
+		arm_bmu_event_start(event, 0);
+	return 0;
+}
+
+static void arm_bmu_event_del(struct perf_event *event, int flags)
+{
+	struct arm_bmu_pmu *pmu = to_bmu_pmu(event);
+
+	arm_bmu_event_stop(event, PERF_EF_UPDATE);
+	pmu->evcnt[event->hw.idx] = NULL;
+}
+
+static void arm_bmu_pmu_irq(struct arm_bmu_pmu *pmu)
+{
+	u32 reg = readl_relaxed(pmu->base + PMOVSCLR);
+	u64 __iomem *pmevcnt = pmu->base + PMEVCNTR_LO;
+
+	for (int i = 0; i < PMU_MAX_COUNTERS; i++) {
+		if (!(reg & (1U << i)))
+			continue;
+		if (WARN_ON(!pmu->evcnt[i]))
+			continue;
+		arm_bmu_event_read(pmu->evcnt[i]);
+		local64_set(&pmu->evcnt[i]->hw.prev_count, S64_MIN);
+		lo_hi_writeq_relaxed(S64_MIN, pmevcnt + i);
+	}
+	writel_relaxed(reg, pmu->base + PMOVSCLR);
+}
+
+static irqreturn_t arm_bmu_handle_irq(int irq, void *dev_id)
+{
+	struct arm_bmu *bmu = dev_id;
+	u32 reg = readl_relaxed(bmu->base + MCU_PMU_INTERRUPT_STATUS);
+	irqreturn_t ret = reg ? IRQ_HANDLED : IRQ_NONE;
+
+	for (int i = 0; i < bmu->num_imus && reg; i++, reg >>= 1) {
+		if (reg & 1)
+			arm_bmu_pmu_irq(bmu->imus + i);
+	}
+	return ret;
+}
+
+static int arm_bmu_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	const struct resource *res;
+	struct arm_bmu *bmu;
+	const char *name = NULL;
+	void __iomem *base;
+	static atomic_t n;
+	int err, num, sz, off;
+	u64 cfg;
+	u32 reg;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -EINVAL;
+
+	/* PMUs and MPAM MSCs are intermingled so we can't claim the whole resource */
+	base = devm_ioremap(dev, res->start, resource_size(res));
+	if (IS_ERR(base))
+		return PTR_ERR(base);
+
+	/* Global and per-PMU-page security all defaults to Root/Secure only */
+	writel_relaxed(1, base + MCU_PMU_GLOBAL_EN);
+	reg = readl_relaxed(base + MCU_PMU_GLOBAL_EN);
+	if (reg != 1)
+		return dev_err_probe(dev, -ENODEV, "Non-Secure access to BMU not enabled?\n");
+	writel_relaxed(0, base + MCU_PMU_GLOBAL_EN);
+
+	cfg = lo_hi_readq_relaxed(base + MCU_CONFIG);
+	num = 1 + FIELD_GET(MCUCFG_NUM_IMU_MONITORS, cfg);
+	/* We don't expect to have dual-page complications to worry about */
+	sz = FIELD_GET(MCUCFG_PMU_ELEMENT_SIZE, cfg);
+	if (sz != 1)
+		return dev_err_probe(dev, -EINVAL, "PMU_ELEMENT_SIZE 0x%x not supported\n", sz);
+
+	/* The PMU pages *are* exclusively ours */
+	off = SZ_4K * FIELD_GET(MCUCFG_PMU_ELEMENT_START, cfg);
+	if (!devm_request_mem_region(dev, res->start + off, num * SZ_4K, dev_name(dev)))
+		return dev_err_probe(dev, err, "Unable to request PMU region\n");
+
+	bmu = devm_kzalloc(dev, struct_size(bmu, imus, num), GFP_KERNEL);
+	if (!bmu)
+		return -ENOMEM;
+
+	bmu->dev = dev;
+	bmu->base = base;
+	bmu->num_imus = num;
+	platform_set_drvdata(pdev, bmu);
+
+	base += off;
+	for (int i = 0; i < bmu->num_imus; i++, base += SZ_4K) {
+		/* At least PMCFGR.SIZE should always be nonzero if visible */
+		reg = readl_relaxed(base + PMCFGR);
+		if (!reg) {
+			dev_warn(dev, "Non-Secure access to PMU %d not enabled?\n", i);
+			num = 0;
+		} else {
+			num = 1 + FIELD_GET(PMCFGR_N, reg);
+		}
+		if (num > PMU_MAX_COUNTERS) {
+			dev_notice(dev, "PMU %d has %d counters, only using %d\n",
+				   i, num, PMU_MAX_COUNTERS);
+			num = PMU_MAX_COUNTERS;
+		}
+		bmu->imus[i].base = base;
+		bmu->imus[i].num_counters = num;
+
+		writel_relaxed(PMCR_P | PMCR_E, base + BMU_PMCR);
+		writel_relaxed(U32_MAX, base + PMCNTENCLR);
+		writel_relaxed(U32_MAX, base + PMOVSCLR);
+		writel_relaxed(U32_MAX, base + PMINTENSET);
+	}
+
+	bmu->cpu = cpumask_local_spread(atomic_fetch_inc(&n), dev_to_node(dev));
+	bmu->irq = platform_get_irq(pdev, 0);
+	if (bmu->irq > 0) {
+		err = devm_request_irq(dev, bmu->irq, arm_bmu_handle_irq,
+				       IRQF_NOBALANCING | IRQF_NO_THREAD,
+				       dev_name(dev), bmu);
+		if (err)
+			bmu->irq = 0;
+		else
+			irq_set_affinity(bmu->irq, cpumask_of(bmu->cpu));
+	}
+	if (!bmu->irq)
+		dev_info(dev, "Continuing without IRQ\n");
+
+	bmu->pmu = (struct pmu) {
+		.module = THIS_MODULE,
+		.parent = dev,
+		.attr_groups = arm_bmu_attr_groups,
+		.capabilities = PERF_PMU_CAP_NO_EXCLUDE,
+		.task_ctx_nr = perf_invalid_context,
+		.pmu_enable = arm_bmu_enable,
+		.pmu_disable = arm_bmu_disable,
+		.event_init = arm_bmu_event_init,
+		.add = arm_bmu_event_add,
+		.del = arm_bmu_event_del,
+		.start = arm_bmu_event_start,
+		.stop = arm_bmu_event_stop,
+		.read = arm_bmu_event_read,
+	};
+
+	if (has_acpi_companion(dev))
+		name = acpi_device_uid(ACPI_COMPANION(dev));
+	else
+		device_property_read_string(dev, "label", &name);
+
+	if (name)
+		name = devm_kasprintf(dev, GFP_KERNEL, "arm_bmu_%s", name);
+	else
+		name = devm_kasprintf(dev, GFP_KERNEL, "arm_bmu_%llx", res->start >> 12);
+	if (!name)
+		return -ENOMEM;
+
+	err = cpuhp_state_add_instance_nocalls(arm_bmu_cpuhp_state, &bmu->cpuhp_node);
+	if (err)
+		return err;
+
+	err = perf_pmu_register(&bmu->pmu, name, -1);
+	if (err)
+		cpuhp_state_remove_instance_nocalls(arm_bmu_cpuhp_state, &bmu->cpuhp_node);
+
+	return err;
+}
+
+static void arm_bmu_remove(struct platform_device *pdev)
+{
+	struct arm_bmu *bmu = platform_get_drvdata(pdev);
+
+	for (int i = 0; i < bmu->num_imus; i++)
+		writel_relaxed(U32_MAX, bmu->imus[i].base + PMINTENCLR);
+
+	perf_pmu_unregister(&bmu->pmu);
+	cpuhp_state_remove_instance_nocalls(arm_bmu_cpuhp_state, &bmu->cpuhp_node);
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id arm_bmu_of_match[] = {
+	{ .compatible = "arm,bus-monitor-unit" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, arm_bmu_of_match);
+#endif
+
+#ifdef CONFIG_ACPI
+static const struct acpi_device_id arm_bmu_acpi_match[] = {
+	{ "ARMHB001" },
+	{}
+};
+MODULE_DEVICE_TABLE(acpi, arm_bmu_acpi_match);
+#endif
+
+static struct platform_driver arm_bmu_driver = {
+	.driver = {
+		.name = "arm-bmu",
+		.of_match_table = of_match_ptr(arm_bmu_of_match),
+		.acpi_match_table = ACPI_PTR(arm_bmu_acpi_match),
+		.suppress_bind_attrs = true,
+	},
+	.probe = arm_bmu_probe,
+	.remove = arm_bmu_remove,
+};
+
+static void arm_bmu_migrate(struct arm_bmu *bmu, unsigned int cpu)
+{
+	perf_pmu_migrate_context(&bmu->pmu, bmu->cpu, cpu);
+	if (bmu->irq)
+		irq_set_affinity(bmu->irq, cpumask_of(cpu));
+	bmu->cpu = cpu;
+}
+
+static int arm_bmu_online_cpu(unsigned int cpu, struct hlist_node *cpuhp_node)
+{
+	struct arm_bmu *bmu;
+	int node;
+
+	bmu = hlist_entry_safe(cpuhp_node, struct arm_bmu, cpuhp_node);
+	node = dev_to_node(bmu->dev);
+	if (cpu_to_node(bmu->cpu) != node && cpu_to_node(cpu) == node)
+		arm_bmu_migrate(bmu, cpu);
+	return 0;
+}
+
+static int arm_bmu_offline_cpu(unsigned int cpu, struct hlist_node *cpuhp_node)
+{
+	struct arm_bmu *bmu;
+	unsigned int target;
+	int node;
+
+	bmu = hlist_entry_safe(cpuhp_node, struct arm_bmu, cpuhp_node);
+	if (cpu != bmu->cpu)
+		return 0;
+
+	node = dev_to_node(bmu->dev);
+	target = cpumask_any_and_but(cpumask_of_node(node), cpu_online_mask, cpu);
+	if (target >= nr_cpu_ids)
+		target = cpumask_any_but(cpu_online_mask, cpu);
+
+	if (target < nr_cpu_ids)
+		arm_bmu_migrate(bmu, target);
+	return 0;
+}
+
+static int __init arm_bmu_init(void)
+{
+	int ret;
+
+	ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "perf/arm/bmu:online",
+				      arm_bmu_online_cpu, arm_bmu_offline_cpu);
+	if (ret < 0)
+		return ret;
+
+	arm_bmu_cpuhp_state = ret;
+
+	ret = platform_driver_register(&arm_bmu_driver);
+	if (ret)
+		cpuhp_remove_multi_state(arm_bmu_cpuhp_state);
+	return ret;
+}
+
+static void __exit arm_bmu_exit(void)
+{
+	platform_driver_unregister(&arm_bmu_driver);
+	cpuhp_remove_multi_state(arm_bmu_cpuhp_state);
+}
+
+module_init(arm_bmu_init);
+module_exit(arm_bmu_exit);
+
+MODULE_DESCRIPTION("ARM Bus Monitor Unit Driver");
+MODULE_LICENSE("GPL v2");
-- 
2.54.0.dirty