[PATCH v3 3/4] drivers: firmware: add riscv SSE support

[Clément Léger]

Add driver level interface to use RISC-V SSE arch support. This interface
allows registering SSE handlers, and receive them. This will be used by
PMU and GHES driver.

Signed-off-by: Himanshu Chauhan <hchauhan@xxxxxxxxxxxxxxxx>
Co-developed-by: Himanshu Chauhan <hchauhan@xxxxxxxxxxxxxxxx>
Signed-off-by: Clément Léger <cleger@xxxxxxxxxxxx>
---
 MAINTAINERS                        |  14 +
 drivers/firmware/Kconfig           |   1 +
 drivers/firmware/Makefile          |   1 +
 drivers/firmware/riscv/Kconfig     |  15 +
 drivers/firmware/riscv/Makefile    |   3 +
 drivers/firmware/riscv/riscv_sse.c | 691 +++++++++++++++++++++++++++++
 include/linux/riscv_sse.h          |  56 +++
 7 files changed, 781 insertions(+)
 create mode 100644 drivers/firmware/riscv/Kconfig
 create mode 100644 drivers/firmware/riscv/Makefile
 create mode 100644 drivers/firmware/riscv/riscv_sse.c
 create mode 100644 include/linux/riscv_sse.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 686109008d8e..a3ddde7fe9fb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20125,6 +20125,13 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/iommu/linux.git
 F:	Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
 F:	drivers/iommu/riscv/
 
+RISC-V FIRMWARE DRIVERS
+M:	Conor Dooley <conor@xxxxxxxxxx>
+L:	linux-riscv@xxxxxxxxxxxxxxxxxxx
+S:	Maintained
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/conor/linux.git
+F:	drivers/firmware/riscv/*
+
 RISC-V MICROCHIP FPGA SUPPORT
 M:	Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
 M:	Daire McNamara <daire.mcnamara@xxxxxxxxxxxxx>
@@ -20177,6 +20184,13 @@ F:	drivers/perf/riscv_pmu.c
 F:	drivers/perf/riscv_pmu_legacy.c
 F:	drivers/perf/riscv_pmu_sbi.c
 
+RISC-V SSE DRIVER
+M:	Clément Léger <cleger@xxxxxxxxxxxx>
+L:	linux-riscv@xxxxxxxxxxxxxxxxxxx
+S:	Maintained
+F:	drivers/firmware/riscv/riscv_sse.c
+F:	include/linux/riscv_sse.h
+
 RISC-V THEAD SoC SUPPORT
 M:	Drew Fustini <drew@xxxxxxxx>
 M:	Guo Ren <guoren@xxxxxxxxxx>
diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index 71d8b26c4103..9e996a1fd511 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -267,6 +267,7 @@ source "drivers/firmware/meson/Kconfig"
 source "drivers/firmware/microchip/Kconfig"
 source "drivers/firmware/psci/Kconfig"
 source "drivers/firmware/qcom/Kconfig"
+source "drivers/firmware/riscv/Kconfig"
 source "drivers/firmware/smccc/Kconfig"
 source "drivers/firmware/tegra/Kconfig"
 source "drivers/firmware/xilinx/Kconfig"
diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
index 7a8d486e718f..c0f5009949a8 100644
--- a/drivers/firmware/Makefile
+++ b/drivers/firmware/Makefile
@@ -33,6 +33,7 @@ obj-y				+= efi/
 obj-y				+= imx/
 obj-y				+= psci/
 obj-y				+= qcom/
+obj-y				+= riscv/
 obj-y				+= smccc/
 obj-y				+= tegra/
 obj-y				+= xilinx/
diff --git a/drivers/firmware/riscv/Kconfig b/drivers/firmware/riscv/Kconfig
new file mode 100644
index 000000000000..8056ed3262d9
--- /dev/null
+++ b/drivers/firmware/riscv/Kconfig
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menu "Risc-V Specific firmware drivers"
+depends on RISCV
+
+config RISCV_SSE
+	bool "Enable SBI Supervisor Software Events support"
+	depends on RISCV_SBI
+	default y
+	help
+	  The Supervisor Software Events support allow the SBI to deliver
+	  NMI-like notifications to the supervisor mode software. When enable,
+	  this option provides support to register callbacks on specific SSE
+	  events.
+
+endmenu
diff --git a/drivers/firmware/riscv/Makefile b/drivers/firmware/riscv/Makefile
new file mode 100644
index 000000000000..4ccfcbbc28ea
--- /dev/null
+++ b/drivers/firmware/riscv/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_RISCV_SSE)		+= riscv_sse.o
diff --git a/drivers/firmware/riscv/riscv_sse.c b/drivers/firmware/riscv/riscv_sse.c
new file mode 100644
index 000000000000..c165e32cc9a5
--- /dev/null
+++ b/drivers/firmware/riscv/riscv_sse.c
@@ -0,0 +1,691 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024 Rivos Inc.
+ */
+
+#define pr_fmt(fmt) "sse: " fmt
+
+#include <linux/cpu.h>
+#include <linux/cpuhotplug.h>
+#include <linux/cpu_pm.h>
+#include <linux/hardirq.h>
+#include <linux/list.h>
+#include <linux/percpu-defs.h>
+#include <linux/reboot.h>
+#include <linux/riscv_sse.h>
+#include <linux/slab.h>
+
+#include <asm/sbi.h>
+#include <asm/sse.h>
+
+struct sse_event {
+	struct list_head list;
+	u32 evt;
+	u32 priority;
+	sse_event_handler *handler;
+	void *handler_arg;
+	bool is_enabled;
+	/* Only valid for global events */
+	unsigned int cpu;
+
+	union {
+		struct sse_registered_event *global;
+		struct sse_registered_event __percpu *local;
+	};
+};
+
+static int sse_hp_state;
+static bool sse_available;
+static DEFINE_SPINLOCK(events_list_lock);
+static LIST_HEAD(events);
+static DEFINE_MUTEX(sse_mutex);
+
+struct sse_registered_event {
+	struct sse_event_arch_data arch;
+	struct sse_event *evt;
+	unsigned long attr_buf;
+};
+
+void sse_handle_event(struct sse_event_arch_data *arch_event,
+		      struct pt_regs *regs)
+{
+	int ret;
+	struct sse_registered_event *reg_evt =
+		container_of(arch_event, struct sse_registered_event, arch);
+	struct sse_event *evt = reg_evt->evt;
+
+	ret = evt->handler(evt->evt, evt->handler_arg, regs);
+	if (ret)
+		pr_warn("event %x handler failed with error %d\n", evt->evt,
+			ret);
+}
+
+static bool sse_event_is_global(u32 evt)
+{
+	return !!(evt & SBI_SSE_EVENT_GLOBAL);
+}
+
+static
+struct sse_event *sse_event_get(u32 evt)
+{
+	struct sse_event *sse_evt = NULL, *tmp;
+
+	scoped_guard(spinlock, &events_list_lock) {
+		list_for_each_entry(tmp, &events, list) {
+			if (tmp->evt == evt) {
+				return sse_evt;
+			}
+		}
+	}
+
+	return NULL;
+}
+
+static phys_addr_t sse_event_get_phys(struct sse_registered_event *reg_evt,
+				      void *addr)
+{
+	phys_addr_t phys;
+
+	if (sse_event_is_global(reg_evt->evt->evt))
+		phys = virt_to_phys(addr);
+	else
+		phys = per_cpu_ptr_to_phys(addr);
+
+	return phys;
+}
+
+static int sse_sbi_event_func(struct sse_event *event, unsigned long func)
+{
+	struct sbiret ret;
+	u32 evt = event->evt;
+
+	ret = sbi_ecall(SBI_EXT_SSE, func, evt, 0, 0, 0, 0, 0);
+	if (ret.error)
+		pr_debug("Failed to execute func %lx, event %x, error %ld\n",
+			 func, evt, ret.error);
+
+	return sbi_err_map_linux_errno(ret.error);
+}
+
+static int sse_sbi_disable_event(struct sse_event *event)
+{
+	return sse_sbi_event_func(event, SBI_SSE_EVENT_DISABLE);
+}
+
+static int sse_sbi_enable_event(struct sse_event *event)
+{
+	return sse_sbi_event_func(event, SBI_SSE_EVENT_ENABLE);
+}
+
+static int sse_event_attr_get_no_lock(struct sse_registered_event *reg_evt,
+				      unsigned long attr_id, unsigned long *val)
+{
+	struct sbiret sret;
+	u32 evt = reg_evt->evt->evt;
+	unsigned long phys;
+
+	phys = sse_event_get_phys(reg_evt, &reg_evt->attr_buf);
+
+	sret = sbi_ecall(SBI_EXT_SSE, SBI_SSE_EVENT_ATTR_READ, evt,
+				     attr_id, 1, phys, 0, 0);
+	if (sret.error) {
+		pr_debug("Failed to get event %x attr %lx, error %ld\n", evt,
+			 attr_id, sret.error);
+		return sbi_err_map_linux_errno(sret.error);
+	}
+
+	*val = reg_evt->attr_buf;
+
+	return 0;
+}
+
+static int sse_event_attr_set_nolock(struct sse_registered_event *reg_evt,
+				     unsigned long attr_id, unsigned long val)
+{
+	struct sbiret sret;
+	u32 evt = reg_evt->evt->evt;
+	unsigned long phys;
+
+	reg_evt->attr_buf = val;
+	phys = sse_event_get_phys(reg_evt, &reg_evt->attr_buf);
+
+	sret = sbi_ecall(SBI_EXT_SSE, SBI_SSE_EVENT_ATTR_WRITE, evt,
+				     attr_id, 1, phys, 0, 0);
+	if (sret.error && sret.error != SBI_ERR_INVALID_STATE) {
+		pr_debug("Failed to set event %x attr %lx, error %ld\n", evt,
+			 attr_id, sret.error);
+		return sbi_err_map_linux_errno(sret.error);
+	}
+
+	return 0;
+}
+
+static int sse_event_set_target_cpu_nolock(struct sse_event *event,
+					   unsigned int cpu)
+{
+	unsigned int hart_id = cpuid_to_hartid_map(cpu);
+	struct sse_registered_event *reg_evt = event->global;
+	u32 evt = event->evt;
+	bool was_enabled;
+	int ret;
+
+	if (!sse_event_is_global(evt))
+		return -EINVAL;
+
+	was_enabled = event->is_enabled;
+	if (was_enabled)
+		sse_sbi_disable_event(event);
+	do {
+		ret = sse_event_attr_set_nolock(reg_evt,
+						SBI_SSE_ATTR_PREFERRED_HART,
+						hart_id);
+	} while (ret == -EINVAL);
+
+	if (ret == 0)
+		event->cpu = cpu;
+
+	if (was_enabled)
+		sse_sbi_enable_event(event);
+
+	return 0;
+}
+
+int sse_event_set_target_cpu(struct sse_event *event, unsigned int cpu)
+{
+	int ret;
+
+	scoped_guard(mutex, &sse_mutex) {
+		cpus_read_lock();
+
+		if (!cpu_online(cpu))
+			return -EINVAL;
+
+		ret = sse_event_set_target_cpu_nolock(event, cpu);
+
+		cpus_read_unlock();
+	}
+
+	return ret;
+}
+
+static int sse_event_init_registered(unsigned int cpu,
+				     struct sse_registered_event *reg_evt,
+				     struct sse_event *event)
+{
+	reg_evt->evt = event;
+	arch_sse_init_event(&reg_evt->arch, event->evt, cpu);
+
+	return 0;
+}
+
+static void sse_event_free_registered(struct sse_registered_event *reg_evt)
+{
+	arch_sse_free_event(&reg_evt->arch);
+}
+
+static int sse_event_alloc_global(struct sse_event *event)
+{
+	int err;
+	struct sse_registered_event *reg_evt;
+
+	reg_evt = kzalloc(sizeof(*reg_evt), GFP_KERNEL);
+	if (!reg_evt)
+		return -ENOMEM;
+
+	event->global = reg_evt;
+	err = sse_event_init_registered(smp_processor_id(), reg_evt,
+					event);
+	if (err)
+		kfree(reg_evt);
+
+	return err;
+}
+
+static int sse_event_alloc_local(struct sse_event *event)
+{
+	int err;
+	unsigned int cpu, err_cpu;
+	struct sse_registered_event *reg_evt;
+	struct sse_registered_event __percpu *reg_evts;
+
+	reg_evts = alloc_percpu(struct sse_registered_event);
+	if (!reg_evts)
+		return -ENOMEM;
+
+	event->local = reg_evts;
+
+	for_each_possible_cpu(cpu) {
+		reg_evt = per_cpu_ptr(reg_evts, cpu);
+		err = sse_event_init_registered(cpu, reg_evt, event);
+		if (err) {
+			err_cpu = cpu;
+			goto err_free_per_cpu;
+		}
+	}
+
+	return 0;
+
+err_free_per_cpu:
+	for_each_possible_cpu(cpu) {
+		if (cpu == err_cpu)
+			break;
+		reg_evt = per_cpu_ptr(reg_evts, cpu);
+		sse_event_free_registered(reg_evt);
+	}
+
+	free_percpu(reg_evts);
+
+	return err;
+}
+
+static struct sse_event *sse_event_alloc(u32 evt,
+					 u32 priority,
+					 sse_event_handler *handler, void *arg)
+{
+	int err;
+	struct sse_event *event;
+
+	event = kzalloc(sizeof(*event), GFP_KERNEL);
+	if (!event)
+		return ERR_PTR(-ENOMEM);
+
+	event->evt = evt;
+	event->priority = priority;
+	event->handler_arg = arg;
+	event->handler = handler;
+
+	if (sse_event_is_global(evt)) {
+		err = sse_event_alloc_global(event);
+		if (err)
+			goto err_alloc_reg_evt;
+	} else {
+		err = sse_event_alloc_local(event);
+		if (err)
+			goto err_alloc_reg_evt;
+	}
+
+	return event;
+
+err_alloc_reg_evt:
+	kfree(event);
+
+	return ERR_PTR(err);
+}
+
+static int sse_sbi_register_event(struct sse_event *event,
+				  struct sse_registered_event *reg_evt)
+{
+	int ret;
+
+	ret = sse_event_attr_set_nolock(reg_evt, SBI_SSE_ATTR_PRIO,
+					event->priority);
+	if (ret)
+		return ret;
+
+	return arch_sse_register_event(&reg_evt->arch);
+}
+
+static int sse_event_register_local(struct sse_event *event)
+{
+	int ret;
+	struct sse_registered_event *reg_evt = per_cpu_ptr(event->local,
+							   smp_processor_id());
+
+	ret = sse_sbi_register_event(event, reg_evt);
+	if (ret)
+		pr_debug("Failed to register event %x: err %d\n", event->evt,
+			 ret);
+
+	return ret;
+}
+
+
+static int sse_sbi_unregister_event(struct sse_event *event)
+{
+	return sse_sbi_event_func(event, SBI_SSE_EVENT_UNREGISTER);
+}
+
+struct sse_per_cpu_evt {
+	struct sse_event *event;
+	unsigned long func;
+	atomic_t error;
+};
+
+static void sse_event_per_cpu_func(void *info)
+{
+	int ret;
+	struct sse_per_cpu_evt *cpu_evt = info;
+
+	if (cpu_evt->func == SBI_SSE_EVENT_REGISTER)
+		ret = sse_event_register_local(cpu_evt->event);
+	else
+		ret = sse_sbi_event_func(cpu_evt->event, cpu_evt->func);
+
+	if (ret)
+		atomic_set(&cpu_evt->error, ret);
+}
+
+static void sse_event_free(struct sse_event *event)
+{
+	unsigned int cpu;
+	struct sse_registered_event *reg_evt;
+
+	if (sse_event_is_global(event->evt)) {
+		sse_event_free_registered(event->global);
+		kfree(event->global);
+	} else {
+		for_each_possible_cpu(cpu) {
+			reg_evt = per_cpu_ptr(event->local, cpu);
+			sse_event_free_registered(reg_evt);
+		}
+		free_percpu(event->local);
+	}
+
+	kfree(event);
+}
+
+int sse_event_enable(struct sse_event *event)
+{
+	int ret = 0;
+	struct sse_per_cpu_evt cpu_evt;
+
+	scoped_guard(mutex, &sse_mutex) {
+		cpus_read_lock();
+		if (sse_event_is_global(event->evt)) {
+			ret = sse_sbi_enable_event(event);
+		} else {
+			cpu_evt.event = event;
+			atomic_set(&cpu_evt.error, 0);
+			cpu_evt.func = SBI_SSE_EVENT_ENABLE;
+			on_each_cpu(sse_event_per_cpu_func, &cpu_evt, 1);
+			ret = atomic_read(&cpu_evt.error);
+			if (ret) {
+				cpu_evt.func = SBI_SSE_EVENT_DISABLE;
+				on_each_cpu(sse_event_per_cpu_func, &cpu_evt,
+					    1);
+			}
+		}
+		cpus_read_unlock();
+
+		if (ret == 0)
+			event->is_enabled = true;
+	}
+
+	return ret;
+}
+
+static void sse_events_mask(void)
+{
+	sbi_ecall(SBI_EXT_SSE, SBI_SSE_EVENT_HART_MASK, 0, 0, 0, 0, 0, 0);
+}
+
+static void sse_events_unmask(void)
+{
+	sbi_ecall(SBI_EXT_SSE, SBI_SSE_EVENT_HART_UNMASK, 0, 0, 0, 0, 0, 0);
+}
+
+static void sse_event_disable_nolock(struct sse_event *event)
+{
+	struct sse_per_cpu_evt cpu_evt;
+
+	if (sse_event_is_global(event->evt)) {
+		sse_sbi_disable_event(event);
+	} else {
+		cpu_evt.event = event;
+		cpu_evt.func = SBI_SSE_EVENT_DISABLE;
+		on_each_cpu(sse_event_per_cpu_func, &cpu_evt, 1);
+	}
+}
+
+void sse_event_disable(struct sse_event *event)
+{
+	scoped_guard(mutex, &sse_mutex) {
+		cpus_read_lock();
+		sse_event_disable_nolock(event);
+		event->is_enabled = false;
+		cpus_read_unlock();
+	}
+}
+
+struct sse_event *sse_event_register(u32 evt, u32 priority,
+				     sse_event_handler *handler, void *arg)
+{
+	struct sse_per_cpu_evt cpu_evt;
+	struct sse_event *event;
+	int ret = 0;
+
+	if (!sse_available)
+		return ERR_PTR(-EOPNOTSUPP);
+
+	mutex_lock(&sse_mutex);
+	if (sse_event_get(evt)) {
+		pr_debug("Event %x already registered\n", evt);
+		ret = -EEXIST;
+		goto out_unlock;
+	}
+
+	event = sse_event_alloc(evt, priority, handler, arg);
+	if (IS_ERR(event)) {
+		ret = PTR_ERR(event);
+		goto out_unlock;
+	}
+
+	cpus_read_lock();
+	if (sse_event_is_global(evt)) {
+		unsigned long preferred_hart;
+
+		ret = sse_event_attr_get_no_lock(event->global,
+						 SBI_SSE_ATTR_PREFERRED_HART,
+						 &preferred_hart);
+		if (ret)
+			goto err_event_free;
+		event->cpu = riscv_hartid_to_cpuid(preferred_hart);
+
+		ret = sse_sbi_register_event(event, event->global);
+		if (ret)
+			goto err_event_free;
+
+	} else {
+		cpu_evt.event = event;
+		atomic_set(&cpu_evt.error, 0);
+		cpu_evt.func = SBI_SSE_EVENT_REGISTER;
+		on_each_cpu(sse_event_per_cpu_func, &cpu_evt, 1);
+		ret = atomic_read(&cpu_evt.error);
+		if (ret) {
+			cpu_evt.func = SBI_SSE_EVENT_UNREGISTER;
+			on_each_cpu(sse_event_per_cpu_func, &cpu_evt, 1);
+			goto err_event_free;
+		}
+	}
+	cpus_read_unlock();
+
+	scoped_guard(spinlock, &events_list_lock)
+		list_add(&event->list, &events);
+
+	mutex_unlock(&sse_mutex);
+
+	return event;
+
+err_event_free:
+	cpus_read_unlock();
+	sse_event_free(event);
+out_unlock:
+	mutex_unlock(&sse_mutex);
+
+	return ERR_PTR(ret);
+}
+
+static void sse_event_unregister_nolock(struct sse_event *event)
+{
+	struct sse_per_cpu_evt cpu_evt;
+
+	if (sse_event_is_global(event->evt)) {
+		sse_sbi_unregister_event(event);
+	} else {
+		cpu_evt.event = event;
+		cpu_evt.func = SBI_SSE_EVENT_UNREGISTER;
+		on_each_cpu(sse_event_per_cpu_func, &cpu_evt, 1);
+	}
+}
+
+void sse_event_unregister(struct sse_event *event)
+{
+	scoped_guard(mutex, &sse_mutex) {
+		cpus_read_lock();
+		sse_event_unregister_nolock(event);
+		cpus_read_unlock();
+
+		scoped_guard(spinlock, &events_list_lock)
+			list_del(&event->list);
+
+		sse_event_free(event);
+	}
+}
+
+static int sse_cpu_online(unsigned int cpu)
+{
+	struct sse_event *sse_evt;
+
+	scoped_guard(spinlock, &events_list_lock) {
+		list_for_each_entry(sse_evt, &events, list) {
+			if (sse_event_is_global(sse_evt->evt))
+				continue;
+
+			sse_event_register_local(sse_evt);
+			if (sse_evt->is_enabled)
+				sse_sbi_enable_event(sse_evt);
+		}
+	}
+
+	/* Ready to handle events. Unmask SSE. */
+	sse_events_unmask();
+
+	return 0;
+}
+
+static int sse_cpu_teardown(unsigned int cpu)
+{
+	unsigned int next_cpu;
+	struct sse_event *sse_evt;
+
+	/* Mask the sse events */
+	sse_events_mask();
+
+	scoped_guard(spinlock, &events_list_lock) {
+		list_for_each_entry(sse_evt, &events, list) {
+			if (!sse_event_is_global(sse_evt->evt)) {
+
+				if (sse_evt->is_enabled)
+					sse_sbi_disable_event(sse_evt);
+
+				sse_sbi_unregister_event(sse_evt);
+				continue;
+			}
+
+			if (sse_evt->cpu != smp_processor_id())
+				continue;
+
+			/* Update destination hart for global event */
+			next_cpu = cpumask_any_but(cpu_online_mask, cpu);
+			sse_event_set_target_cpu_nolock(sse_evt, next_cpu);
+		}
+	}
+
+	return 0;
+}
+
+static void sse_reset(void)
+{
+	struct sse_event *event = NULL;
+
+	list_for_each_entry(event, &events, list) {
+		sse_event_disable_nolock(event);
+		sse_event_unregister_nolock(event);
+	}
+}
+
+static int sse_pm_notifier(struct notifier_block *nb, unsigned long action,
+			   void *data)
+{
+	WARN_ON_ONCE(preemptible());
+
+	switch (action) {
+	case CPU_PM_ENTER:
+		sse_events_mask();
+		break;
+	case CPU_PM_EXIT:
+	case CPU_PM_ENTER_FAILED:
+		sse_events_unmask();
+		break;
+	default:
+		return NOTIFY_DONE;
+	}
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block sse_pm_nb = {
+	.notifier_call = sse_pm_notifier,
+};
+
+/*
+ * Mask all CPUs and unregister all events on panic, reboot or kexec.
+ */
+static int sse_reboot_notifier(struct notifier_block *nb, unsigned long action,
+				void *data)
+{
+	cpuhp_remove_state(sse_hp_state);
+
+	sse_reset();
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block sse_reboot_nb = {
+	.notifier_call = sse_reboot_notifier,
+};
+
+static int __init sse_init(void)
+{
+	int cpu, ret;
+
+	if (sbi_probe_extension(SBI_EXT_SSE) <= 0) {
+		pr_err("Missing SBI SSE extension\n");
+		return -EOPNOTSUPP;
+	}
+	pr_info("SBI SSE extension detected\n");
+
+	for_each_possible_cpu(cpu)
+		INIT_LIST_HEAD(&events);
+
+	ret = cpu_pm_register_notifier(&sse_pm_nb);
+	if (ret) {
+		pr_warn("Failed to register CPU PM notifier...\n");
+		return ret;
+	}
+
+	ret = register_reboot_notifier(&sse_reboot_nb);
+	if (ret) {
+		pr_warn("Failed to register reboot notifier...\n");
+		goto remove_cpupm;
+	}
+
+	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "riscv/sse:online",
+				sse_cpu_online, sse_cpu_teardown);
+	if (ret < 0)
+		goto remove_reboot;
+
+	sse_hp_state = ret;
+	sse_available = true;
+
+	return 0;
+
+remove_reboot:
+	unregister_reboot_notifier(&sse_reboot_nb);
+
+remove_cpupm:
+	cpu_pm_unregister_notifier(&sse_pm_nb);
+
+	return ret;
+}
+arch_initcall(sse_init);
diff --git a/include/linux/riscv_sse.h b/include/linux/riscv_sse.h
new file mode 100644
index 000000000000..c73184074b8c
--- /dev/null
+++ b/include/linux/riscv_sse.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2024 Rivos Inc.
+ */
+
+#ifndef __LINUX_RISCV_SSE_H
+#define __LINUX_RISCV_SSE_H
+
+#include <linux/types.h>
+#include <linux/linkage.h>
+
+struct sse_event;
+struct pt_regs;
+
+typedef int (sse_event_handler)(u32 event_num, void *arg, struct pt_regs *regs);
+
+#ifdef CONFIG_RISCV_SSE
+
+struct sse_event *sse_event_register(u32 event_num, u32 priority,
+				     sse_event_handler *handler, void *arg);
+
+void sse_event_unregister(struct sse_event *evt);
+
+int sse_event_set_target_cpu(struct sse_event *sse_evt, unsigned int cpu);
+
+int sse_event_enable(struct sse_event *sse_evt);
+
+void sse_event_disable(struct sse_event *sse_evt);
+
+#else
+static inline struct sse_event *sse_event_register(u32 event_num, u32 priority,
+						   sse_event_handler *handler,
+						   void *arg)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline void sse_event_unregister(struct sse_event *evt) {}
+
+static inline int sse_event_set_target_cpu(struct sse_event *sse_evt,
+					   unsigned int cpu)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int sse_event_enable(struct sse_event *sse_evt)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void sse_event_disable(struct sse_event *sse_evt) {}
+
+
+#endif
+
+#endif /* __LINUX_RISCV_SSE_H */
-- 
2.45.2