[RFC PATCH v2 6/8] cpuidle: Add RISC-V SBI CPU idle driver

[Anup Patel]

The RISC-V SBI HSM extension provides HSM suspend call which can
be used by Linux RISC-V to enter platform specific low-power state.

This patch adds a CPU idle driver based on RISC-V SBI calls which
will populate idle states from device tree and use SBI calls to
entry these idle states.

Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
---
 MAINTAINERS                   |   8 +
 drivers/cpuidle/Kconfig       |   5 +
 drivers/cpuidle/Kconfig.riscv |  15 +
 drivers/cpuidle/Makefile      |   4 +
 drivers/cpuidle/cpuidle-sbi.c | 502 ++++++++++++++++++++++++++++++++++
 5 files changed, 534 insertions(+)
 create mode 100644 drivers/cpuidle/Kconfig.riscv
 create mode 100644 drivers/cpuidle/cpuidle-sbi.c

diff --git a/MAINTAINERS b/MAINTAINERS
index aa84121c5611..4954112efdb4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4679,6 +4679,14 @@ S:	Supported
 F:	drivers/cpuidle/cpuidle-psci.h
 F:	drivers/cpuidle/cpuidle-psci-domain.c
 
+CPUIDLE DRIVER - RISC-V SBI
+M:	Anup Patel <anup.patel@xxxxxxx>
+R:	Sandeep Tripathy <milun.tripathy@xxxxxxxxx>
+L:	linux-pm@xxxxxxxxxxxxxxx
+L:	linux-riscv@xxxxxxxxxxxxxxxxxxx
+S:	Supported
+F:	drivers/cpuidle/cpuidle-sbi.c
+
 CRAMFS FILESYSTEM
 M:	Nicolas Pitre <nico@xxxxxxxxxxx>
 S:	Maintained
diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index f1afe7ab6b54..ff71dd662880 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig
@@ -66,6 +66,11 @@ depends on PPC
 source "drivers/cpuidle/Kconfig.powerpc"
 endmenu
 
+menu "RISC-V CPU Idle Drivers"
+depends on RISCV
+source "drivers/cpuidle/Kconfig.riscv"
+endmenu
+
 config HALTPOLL_CPUIDLE
 	tristate "Halt poll cpuidle driver"
 	depends on X86 && KVM_GUEST
diff --git a/drivers/cpuidle/Kconfig.riscv b/drivers/cpuidle/Kconfig.riscv
new file mode 100644
index 000000000000..78518c26af74
--- /dev/null
+++ b/drivers/cpuidle/Kconfig.riscv
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# RISC-V CPU Idle drivers
+#
+
+config RISCV_SBI_CPUIDLE
+	bool "RISC-V SBI CPU idle Driver"
+	depends on RISCV_SBI
+	select DT_IDLE_STATES
+	select CPU_IDLE_MULTIPLE_DRIVERS
+	select DT_IDLE_GENPD if PM_GENERIC_DOMAINS_OF
+	help
+	  Select this option to enable RISC-V SBI firmware based CPU idle
+	  driver for RISC-V systems. This drivers also supports hierarchical
+	  DT based layout of the idle state.
diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
index 11a26cef279f..a36922c18510 100644
--- a/drivers/cpuidle/Makefile
+++ b/drivers/cpuidle/Makefile
@@ -35,3 +35,7 @@ obj-$(CONFIG_MIPS_CPS_CPUIDLE)		+= cpuidle-cps.o
 # POWERPC drivers
 obj-$(CONFIG_PSERIES_CPUIDLE)		+= cpuidle-pseries.o
 obj-$(CONFIG_POWERNV_CPUIDLE)		+= cpuidle-powernv.o
+
+###############################################################################
+# RISC-V drivers
+obj-$(CONFIG_RISCV_SBI_CPUIDLE)		+= cpuidle-sbi.o
diff --git a/drivers/cpuidle/cpuidle-sbi.c b/drivers/cpuidle/cpuidle-sbi.c
new file mode 100644
index 000000000000..47938fff61e1
--- /dev/null
+++ b/drivers/cpuidle/cpuidle-sbi.c
@@ -0,0 +1,502 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * RISC-V SBI CPU idle driver.
+ *
+ * Copyright (c) 2021 Western Digital Corporation or its affiliates.
+ */
+
+#define pr_fmt(fmt) "cpuidle-sbi: " fmt
+
+#include <linux/cpuidle.h>
+#include <linux/cpumask.h>
+#include <linux/cpu_pm.h>
+#include <linux/cpu_cooling.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/slab.h>
+#include <linux/platform_device.h>
+#include <linux/pm_domain.h>
+#include <linux/pm_runtime.h>
+#include <asm/cpuidle.h>
+#include <asm/sbi.h>
+#include <asm/suspend.h>
+
+#include "dt_idle_states.h"
+#include "dt_idle_genpd.h"
+
+struct sbi_cpuidle_data {
+	u32 *states;
+	struct device *dev;
+};
+
+struct sbi_domain_state {
+	bool available;
+	u32 state;
+};
+
+static DEFINE_PER_CPU_READ_MOSTLY(struct sbi_cpuidle_data, sbi_cpuidle_data);
+static DEFINE_PER_CPU(struct sbi_domain_state, domain_state);
+static bool sbi_cpuidle_use_osi;
+static bool sbi_cpuidle_use_cpuhp;
+static bool sbi_cpuidle_pd_allow_domain_state;
+
+static inline void sbi_set_domain_state(u32 state)
+{
+	struct sbi_domain_state *data = this_cpu_ptr(&domain_state);
+
+	data->available = true;
+	data->state = state;
+}
+
+static inline u32 sbi_get_domain_state(void)
+{
+	struct sbi_domain_state *data = this_cpu_ptr(&domain_state);
+
+	return data->state;
+}
+
+static inline void sbi_clear_domain_state(void)
+{
+	struct sbi_domain_state *data = this_cpu_ptr(&domain_state);
+
+	data->available = false;
+}
+
+static inline bool sbi_is_domain_state_available(void)
+{
+	struct sbi_domain_state *data = this_cpu_ptr(&domain_state);
+
+	return data->available;
+}
+
+static int sbi_suspend_finisher(unsigned long suspend_type,
+				unsigned long resume_addr,
+				unsigned long opaque)
+{
+	struct sbiret ret;
+
+	ret = sbi_ecall(SBI_EXT_HSM, SBI_EXT_HSM_HART_SUSPEND,
+			suspend_type, resume_addr, opaque, 0, 0, 0);
+
+	return (ret.error) ? sbi_err_map_linux_errno(ret.error) : 0;
+}
+
+static int sbi_suspend(u32 state)
+{
+	if (state & SBI_HSM_SUSP_NON_RET_BIT)
+		return cpu_suspend(state, sbi_suspend_finisher);
+	else
+		return sbi_suspend_finisher(state, 0, 0);
+}
+
+static int sbi_cpuidle_enter_state(struct cpuidle_device *dev,
+				   struct cpuidle_driver *drv, int idx)
+{
+	u32 *states = __this_cpu_read(sbi_cpuidle_data.states);
+
+	return CPU_PM_CPU_IDLE_ENTER_PARAM(sbi_suspend, idx, states[idx]);
+}
+
+static int __sbi_enter_domain_idle_state(struct cpuidle_device *dev,
+					  struct cpuidle_driver *drv, int idx,
+					  bool s2idle)
+{
+	struct sbi_cpuidle_data *data = this_cpu_ptr(&sbi_cpuidle_data);
+	u32 *states = data->states;
+	struct device *pd_dev = data->dev;
+	u32 state;
+	int ret;
+
+	ret = cpu_pm_enter();
+	if (ret)
+		return -1;
+
+	/* Do runtime PM to manage a hierarchical CPU toplogy. */
+	rcu_irq_enter_irqson();
+	if (s2idle)
+		dev_pm_genpd_suspend(pd_dev);
+	else
+		pm_runtime_put_sync_suspend(pd_dev);
+	rcu_irq_exit_irqson();
+
+	if (sbi_is_domain_state_available())
+		state = sbi_get_domain_state();
+	else
+		state = states[idx];
+
+	ret = sbi_suspend(state) ? -1 : idx;
+
+	rcu_irq_enter_irqson();
+	if (s2idle)
+		dev_pm_genpd_resume(pd_dev);
+	else
+		pm_runtime_get_sync(pd_dev);
+	rcu_irq_exit_irqson();
+
+	cpu_pm_exit();
+
+	/* Clear the domain state to start fresh when back from idle. */
+	sbi_clear_domain_state();
+	return ret;
+}
+
+static int sbi_enter_domain_idle_state(struct cpuidle_device *dev,
+				       struct cpuidle_driver *drv, int idx)
+{
+	return __sbi_enter_domain_idle_state(dev, drv, idx, false);
+}
+
+static int sbi_enter_s2idle_domain_idle_state(struct cpuidle_device *dev,
+					      struct cpuidle_driver *drv,
+					      int idx)
+{
+	return __sbi_enter_domain_idle_state(dev, drv, idx, true);
+}
+
+static int sbi_cpuidle_cpuhp_up(unsigned int cpu)
+{
+	struct device *pd_dev = __this_cpu_read(sbi_cpuidle_data.dev);
+
+	if (pd_dev)
+		pm_runtime_get_sync(pd_dev);
+
+	return 0;
+}
+
+static int sbi_cpuidle_cpuhp_down(unsigned int cpu)
+{
+	struct device *pd_dev = __this_cpu_read(sbi_cpuidle_data.dev);
+
+	if (pd_dev) {
+		pm_runtime_put_sync(pd_dev);
+		/* Clear domain state to start fresh at next online. */
+		sbi_clear_domain_state();
+	}
+
+	return 0;
+}
+
+static void sbi_idle_init_cpuhp(void)
+{
+	int err;
+
+	if (!sbi_cpuidle_use_cpuhp)
+		return;
+
+	err = cpuhp_setup_state_nocalls(CPUHP_AP_CPU_PM_STARTING,
+					"cpuidle/sbi:online",
+					sbi_cpuidle_cpuhp_up,
+					sbi_cpuidle_cpuhp_down);
+	if (err)
+		pr_warn("Failed %d while setup cpuhp state\n", err);
+}
+
+static const struct of_device_id sbi_cpuidle_state_match[] = {
+	{ .compatible = "riscv,idle-state",
+	  .data = sbi_cpuidle_enter_state },
+	{ },
+};
+
+static bool sbi_suspend_state_is_valid(u32 state)
+{
+	if (state > SBI_HSM_SUSPEND_RET_DEFAULT &&
+	    state < SBI_HSM_SUSPEND_RET_PLATFORM)
+		return false;
+	if (state > SBI_HSM_SUSPEND_NON_RET_DEFAULT &&
+	    state < SBI_HSM_SUSPEND_NON_RET_PLATFORM)
+		return false;
+	return true;
+}
+
+static int sbi_dt_parse_state_node(struct device_node *np, u32 *state)
+{
+	int err = of_property_read_u32(np, "riscv,sbi-suspend-param", state);
+
+	if (err) {
+		pr_warn("%pOF missing riscv,sbi-suspend-param property\n", np);
+		return err;
+	}
+
+	if (!sbi_suspend_state_is_valid(*state)) {
+		pr_warn("Invalid SBI suspend state %#x\n", *state);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int sbi_dt_cpu_init_topology(struct cpuidle_driver *drv,
+				     struct sbi_cpuidle_data *data,
+				     unsigned int state_count, int cpu)
+{
+	/* Currently limit the hierarchical topology to be used in OSI mode. */
+	if (!sbi_cpuidle_use_osi)
+		return 0;
+
+	data->dev = dt_idle_genpd_attach_cpu(cpu, "sbi");
+	if (IS_ERR_OR_NULL(data->dev))
+		return PTR_ERR_OR_ZERO(data->dev);
+
+	/*
+	 * Using the deepest state for the CPU to trigger a potential selection
+	 * of a shared state for the domain, assumes the domain states are all
+	 * deeper states.
+	 */
+	drv->states[state_count - 1].enter = sbi_enter_domain_idle_state;
+	drv->states[state_count - 1].enter_s2idle = sbi_enter_s2idle_domain_idle_state;
+	sbi_cpuidle_use_cpuhp = true;
+
+	return 0;
+}
+
+static int sbi_cpuidle_dt_init_states(struct device *dev,
+					struct cpuidle_driver *drv,
+					unsigned int cpu,
+					unsigned int state_count)
+{
+	struct sbi_cpuidle_data *data = per_cpu_ptr(&sbi_cpuidle_data, cpu);
+	struct device_node *state_node;
+	struct device_node *cpu_node;
+	u32 *states;
+	int i, ret;
+
+	cpu_node = of_cpu_device_node_get(cpu);
+	if (!cpu_node)
+		return -ENODEV;
+
+	states = devm_kcalloc(dev, state_count, sizeof(*states), GFP_KERNEL);
+	if (!states) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	/* Parse SBI specific details from state DT nodes */
+	for (i = 1; i < state_count; i++) {
+		state_node = of_get_cpu_state_node(cpu_node, i - 1);
+		if (!state_node)
+			break;
+
+		ret = sbi_dt_parse_state_node(state_node, &states[i]);
+		of_node_put(state_node);
+
+		if (ret)
+			return ret;
+
+		pr_debug("sbi-state %#x index %d\n", states[i], i);
+	}
+	if (i != state_count) {
+		ret = -ENODEV;
+		goto fail;
+	}
+
+	/* Initialize optional data, used for the hierarchical topology. */
+	ret = sbi_dt_cpu_init_topology(drv, data, state_count, cpu);
+	if (ret < 0)
+		return ret;
+
+	/* Store states in the per-cpu struct. */
+	data->states = states;
+
+fail:
+	of_node_put(cpu_node);
+
+	return ret;
+}
+
+static void sbi_cpuidle_deinit_cpu(int cpu)
+{
+	struct sbi_cpuidle_data *data = per_cpu_ptr(&sbi_cpuidle_data, cpu);
+
+	dt_idle_genpd_detach_cpu(data->dev);
+	sbi_cpuidle_use_cpuhp = false;
+}
+
+static int sbi_cpuidle_init_cpu(struct device *dev, int cpu)
+{
+	struct cpuidle_driver *drv;
+	unsigned int state_count = 0;
+	int ret = 0;
+
+	drv = devm_kzalloc(dev, sizeof(*drv), GFP_KERNEL);
+	if (!drv)
+		return -ENOMEM;
+
+	drv->name = "sbi_cpuidle";
+	drv->owner = THIS_MODULE;
+	drv->cpumask = (struct cpumask *)cpumask_of(cpu);
+
+	/* RISC-V architectural WFI to be represented as state index 0. */
+	drv->states[0].enter = sbi_cpuidle_enter_state;
+	drv->states[0].exit_latency = 1;
+	drv->states[0].target_residency = 1;
+	drv->states[0].power_usage = UINT_MAX;
+	strcpy(drv->states[0].name, "WFI");
+	strcpy(drv->states[0].desc, "RISC-V WFI");
+
+	/*
+	 * If no DT idle states are detected (ret == 0) let the driver
+	 * initialization fail accordingly since there is no reason to
+	 * initialize the idle driver if only wfi is supported, the
+	 * default archictectural back-end already executes wfi
+	 * on idle entry.
+	 */
+	ret = dt_init_idle_driver(drv, sbi_cpuidle_state_match, 1);
+	if (ret <= 0) {
+		pr_debug("HART%ld: failed to parse DT idle states\n",
+			 cpuid_to_hartid_map(cpu));
+		return ret ? : -ENODEV;
+	}
+	state_count = ret + 1; /* Include WFI state as well */
+
+	/* Initialize idle states from DT. */
+	ret = sbi_cpuidle_dt_init_states(dev, drv, cpu, state_count);
+	if (ret) {
+		pr_err("HART%ld: failed to init idle states\n",
+		       cpuid_to_hartid_map(cpu));
+		return ret;
+	}
+
+	ret = cpuidle_register(drv, NULL);
+	if (ret)
+		goto deinit;
+
+	cpuidle_cooling_register(drv);
+
+	return 0;
+deinit:
+	sbi_cpuidle_deinit_cpu(cpu);
+	return ret;
+}
+
+static int sbi_cpuidle_pd_power_off(struct generic_pm_domain *pd)
+{
+	struct genpd_power_state *state = &pd->states[pd->state_idx];
+	u32 *pd_state;
+
+	if (!state->data)
+		return 0;
+
+	if (!sbi_cpuidle_pd_allow_domain_state)
+		return -EBUSY;
+
+	/* OSI mode is enabled, set the corresponding domain state. */
+	pd_state = state->data;
+	sbi_set_domain_state(*pd_state);
+
+	return 0;
+}
+
+static void sbi_cpuidle_domain_sync_state(struct device *dev)
+{
+	/*
+	 * All devices have now been attached/probed to the PM domain
+	 * topology, hence it's fine to allow domain states to be picked.
+	 */
+	sbi_cpuidle_pd_allow_domain_state = true;
+}
+
+static struct dt_idle_genpd_ops sbi_genpd_ops = {
+	.parse_state_node = sbi_dt_parse_state_node,
+};
+
+static int sbi_cpuidle_probe(struct platform_device *pdev)
+{
+	int cpu, ret;
+	struct cpuidle_driver *drv;
+	struct cpuidle_device *dev;
+	struct device_node *np, *pds_node;
+
+	/* Detect OSI support based on CPU DT nodes */
+	sbi_cpuidle_use_osi = true;
+	for_each_possible_cpu(cpu) {
+		np = of_cpu_device_node_get(cpu);
+		if (np &&
+		    of_find_property(np, "power-domains", NULL) &&
+		    of_find_property(np, "power-domain-names", NULL)) {
+			continue;
+		} else {
+			sbi_cpuidle_use_osi = false;
+			break;
+		}
+	}
+
+	if (sbi_cpuidle_use_osi)
+		sbi_genpd_ops.power_off = sbi_cpuidle_pd_power_off;
+
+	/* Populate generic power domains from DT nodes */
+	pds_node = of_find_node_by_path("/cpus/power-domains");
+	if (pds_node) {
+		ret = dt_idle_genpd_probe(&sbi_genpd_ops, pds_node);
+		of_node_put(pds_node);
+		if (ret)
+			return ret;
+	}
+
+	/* Initialize CPU idle driver for each CPU */
+	for_each_possible_cpu(cpu) {
+		ret = sbi_cpuidle_init_cpu(&pdev->dev, cpu);
+		if (ret) {
+			pr_debug("HART%ld: idle driver init failed\n",
+				 cpuid_to_hartid_map(cpu));
+			goto out_fail;
+		}
+	}
+
+	/* Setup CPU hotplut notifiers */
+	sbi_idle_init_cpuhp();
+
+	pr_info("idle driver registered for all CPUs\n");
+
+	return 0;
+
+out_fail:
+	while (--cpu >= 0) {
+		dev = per_cpu(cpuidle_devices, cpu);
+		drv = cpuidle_get_cpu_driver(dev);
+		cpuidle_unregister(drv);
+		sbi_cpuidle_deinit_cpu(cpu);
+	}
+
+	return ret;
+}
+
+static struct platform_driver sbi_cpuidle_driver = {
+	.probe = sbi_cpuidle_probe,
+	.driver = {
+		.name = "sbi-cpuidle",
+		.sync_state = sbi_cpuidle_domain_sync_state,
+	},
+};
+
+static int __init sbi_cpuidle_init(void)
+{
+	int ret;
+	struct platform_device *pdev;
+
+	/*
+	 * The SBI HSM suspend function is only available when:
+	 * 1) SBI version is 0.3 or higher
+	 * 2) SBI HSM extension is available
+	 */
+	if ((sbi_spec_version < sbi_mk_version(0, 3)) ||
+	    sbi_probe_extension(SBI_EXT_HSM) <= 0) {
+		pr_info("HSM suspend not available\n");
+		return 0;
+	}
+
+	ret = platform_driver_register(&sbi_cpuidle_driver);
+	if (ret)
+		return ret;
+
+	pdev = platform_device_register_simple("sbi-cpuidle",
+						-1, NULL, 0);
+	if (IS_ERR(pdev)) {
+		platform_driver_unregister(&sbi_cpuidle_driver);
+		return PTR_ERR(pdev);
+	}
+
+	return 0;
+}
+device_initcall(sbi_cpuidle_init);
-- 
2.25.1