drivers/irqchip/irq-sifive-plic.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2017 SiFive
  * Copyright (C) 2018 Christoph Hellwig
  */
 #define pr_fmt(fmt) "plic: " fmt
 #include <linux/cpu.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/irq.h>
 #include <linux/irqchip.h>
 #include <linux/irqchip/chained_irq.h>
 #include <linux/irqdomain.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
 #include <linux/platform_device.h>
 #include <linux/spinlock.h>
 #include <asm/smp.h>

 /*
  * This driver implements a version of the RISC-V PLIC with the actual layout
  * specified in chapter 8 of the SiFive U5 Coreplex Series Manual:
  *
  *     https://static.dev.sifive.com/U54-MC-RVCoreIP.pdf
  *
  * The largest number supported by devices marked as 'sifive,plic-1.0.0', is
  * 1024, of which device 0 is defined as non-existent by the RISC-V Privileged
  * Spec.
  */

 #define MAX_DEVICES			1024
 #define MAX_CONTEXTS			15872

 /*
  * Each interrupt source has a priority register associated with it.
  * We always hardwire it to one in Linux.
  */
 #define PRIORITY_BASE			0
 #define     PRIORITY_PER_ID		4

 /*
  * Each hart context has a vector of interrupt enable bits associated with it.
  * There's one bit for each interrupt source.
  */
 #define ENABLE_BASE			0x2000
 #define     ENABLE_PER_HART		0x80

 /*
  * Each hart context has a set of control registers associated with it.  Right
  * now there's only two: a source priority threshold over which the hart will
  * take an interrupt, and a register to claim interrupts.
  */
 #define CONTEXT_BASE			0x200000
 #define     CONTEXT_PER_HART		0x1000
 #define     CONTEXT_THRESHOLD		0x00
 #define     CONTEXT_CLAIM		0x04

 #define	PLIC_DISABLE_THRESHOLD		0x7
 #define	PLIC_ENABLE_THRESHOLD		0

 struct plic_priv {
 	struct cpumask lmask;
 	struct irq_domain *irqdomain;
 	void __iomem *regs;
 };

 struct plic_handler {
 	bool			present;
 	void __iomem		*hart_base;
 	/*
 	 * Protect mask operations on the registers given that we can't
 	 * assume atomic memory operations work on them.
 	 */
 	raw_spinlock_t		enable_lock;
 	void __iomem		*enable_base;
 	struct plic_priv	*priv;
 };
 static int plic_parent_irq __ro_after_init;
 static bool plic_cpuhp_setup_done __ro_after_init;
 static DEFINE_PER_CPU(struct plic_handler, plic_handlers);

 static inline void plic_toggle(struct plic_handler *handler,
 				int hwirq, int enable)
 {
 	u32 __iomem *reg = handler->enable_base + (hwirq / 32) * sizeof(u32);
 	u32 hwirq_mask = 1 << (hwirq % 32);

 	raw_spin_lock(&handler->enable_lock);
 	if (enable)
 		writel(readl(reg) | hwirq_mask, reg);
 	else
 		writel(readl(reg) & ~hwirq_mask, reg);
 	raw_spin_unlock(&handler->enable_lock);
 }

 static inline void plic_irq_toggle(const struct cpumask *mask,
 				   struct irq_data *d, int enable)
 {
 	int cpu;
 	struct plic_priv *priv = irq_data_get_irq_chip_data(d);

 	writel(enable, priv->regs + PRIORITY_BASE + d->hwirq * PRIORITY_PER_ID);
 	for_each_cpu(cpu, mask) {
 		struct plic_handler *handler = per_cpu_ptr(&plic_handlers, cpu);

 		if (handler->present &&
 		    cpumask_test_cpu(cpu, &handler->priv->lmask))
 			plic_toggle(handler, d->hwirq, enable);
 	}
 }

 static void plic_irq_unmask(struct irq_data *d)
 {
 	struct cpumask amask;
 	unsigned int cpu;
 	struct plic_priv *priv = irq_data_get_irq_chip_data(d);

 	cpumask_and(&amask, &priv->lmask, cpu_online_mask);
 	cpu = cpumask_any_and(irq_data_get_affinity_mask(d),
 					   &amask);
 	if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
 		return;
 	plic_irq_toggle(cpumask_of(cpu), d, 1);
 }

 static void plic_irq_mask(struct irq_data *d)
 {
 	struct plic_priv *priv = irq_data_get_irq_chip_data(d);

 	plic_irq_toggle(&priv->lmask, d, 0);
 }

 #ifdef CONFIG_SMP
 static int plic_set_affinity(struct irq_data *d,
 			     const struct cpumask *mask_val, bool force)
 {
 	unsigned int cpu;
 	struct cpumask amask;
 	struct plic_priv *priv = irq_data_get_irq_chip_data(d);

 	cpumask_and(&amask, &priv->lmask, mask_val);

 	if (force)
 		cpu = cpumask_first(&amask);
 	else
 		cpu = cpumask_any_and(&amask, cpu_online_mask);

 	if (cpu >= nr_cpu_ids)
 		return -EINVAL;

 	plic_irq_toggle(&priv->lmask, d, 0);
 	plic_irq_toggle(cpumask_of(cpu), d, !irqd_irq_masked(d));

 	irq_data_update_effective_affinity(d, cpumask_of(cpu));

 	return IRQ_SET_MASK_OK_DONE;
 }
 #endif

 static void plic_irq_eoi(struct irq_data *d)
 {
 	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);

 	writel(d->hwirq, handler->hart_base + CONTEXT_CLAIM);
 }

 static struct irq_chip plic_chip = {
 	.name		= "SiFive PLIC",
 	.irq_mask	= plic_irq_mask,
 	.irq_unmask	= plic_irq_unmask,
 	.irq_eoi	= plic_irq_eoi,
 #ifdef CONFIG_SMP
 	.irq_set_affinity = plic_set_affinity,
 #endif
 };

 static int plic_irqdomain_map(struct irq_domain *d, unsigned int irq,
 			      irq_hw_number_t hwirq)
 {
 	struct plic_priv *priv = d->host_data;

 	irq_domain_set_info(d, irq, hwirq, &plic_chip, d->host_data,
 			    handle_fasteoi_irq, NULL, NULL);
 	irq_set_noprobe(irq);
 	irq_set_affinity(irq, &priv->lmask);
 	return 0;
 }

 static int plic_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
 				 unsigned int nr_irqs, void *arg)
 {
 	int i, ret;
 	irq_hw_number_t hwirq;
 	unsigned int type;
 	struct irq_fwspec *fwspec = arg;

 	ret = irq_domain_translate_onecell(domain, fwspec, &hwirq, &type);
 	if (ret)
 		return ret;

 	for (i = 0; i < nr_irqs; i++) {
 		ret = plic_irqdomain_map(domain, virq + i, hwirq + i);
 		if (ret)
 			return ret;
 	}

 	return 0;
 }

 static const struct irq_domain_ops plic_irqdomain_ops = {
 	.translate	= irq_domain_translate_onecell,
 	.alloc		= plic_irq_domain_alloc,
 	.free		= irq_domain_free_irqs_top,
 };

 /*
  * Handling an interrupt is a two-step process: first you claim the interrupt
  * by reading the claim register, then you complete the interrupt by writing
  * that source ID back to the same claim register.  This automatically enables
  * and disables the interrupt, so there's nothing else to do.
  */
 static void plic_handle_irq(struct irq_desc *desc)
 {
 	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
 	struct irq_chip *chip = irq_desc_get_chip(desc);
 	void __iomem *claim = handler->hart_base + CONTEXT_CLAIM;
 	irq_hw_number_t hwirq;

 	WARN_ON_ONCE(!handler->present);

 	chained_irq_enter(chip, desc);

 	while ((hwirq = readl(claim))) {
 		int irq = irq_find_mapping(handler->priv->irqdomain, hwirq);

 		if (unlikely(irq <= 0))
 			pr_warn_ratelimited("can't find mapping for hwirq %lu\n",
 					hwirq);
 		else
 			generic_handle_irq(irq);
 	}

 	chained_irq_exit(chip, desc);
 }

 static void plic_set_threshold(struct plic_handler *handler, u32 threshold)
 {
 	/* priority must be > threshold to trigger an interrupt */
 	writel(threshold, handler->hart_base + CONTEXT_THRESHOLD);
 }

 static int plic_dying_cpu(unsigned int cpu)
 {
 	if (plic_parent_irq)
 		disable_percpu_irq(plic_parent_irq);

 	return 0;
 }

 static int plic_starting_cpu(unsigned int cpu)
 {
 	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);

 	if (plic_parent_irq)
 		enable_percpu_irq(plic_parent_irq,
 				  irq_get_trigger_type(plic_parent_irq));
 	else
 		pr_warn("cpu%d: parent irq not available\n", cpu);
 	plic_set_threshold(handler, PLIC_ENABLE_THRESHOLD);

 	return 0;
 }

 static int __init plic_init(struct device_node *node,
 		struct device_node *parent)
 {
 	int error = 0, nr_contexts, nr_handlers = 0, i;
 	u32 nr_irqs;
 	struct plic_priv *priv;
 	struct plic_handler *handler;

 	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 	if (!priv)
 		return -ENOMEM;

 	priv->regs = of_iomap(node, 0);
 	if (WARN_ON(!priv->regs)) {
 		error = -EIO;
 		goto out_free_priv;
 	}

 	error = -EINVAL;
 	of_property_read_u32(node, "riscv,ndev", &nr_irqs);
 	if (WARN_ON(!nr_irqs))
 		goto out_iounmap;

 	nr_contexts = of_irq_count(node);
 	if (WARN_ON(!nr_contexts))
 		goto out_iounmap;

 	error = -ENOMEM;
 	priv->irqdomain = irq_domain_add_linear(node, nr_irqs + 1,
 			&plic_irqdomain_ops, priv);
 	if (WARN_ON(!priv->irqdomain))
 		goto out_iounmap;

 	for (i = 0; i < nr_contexts; i++) {
 		struct of_phandle_args parent;
 		irq_hw_number_t hwirq;
 		int cpu, hartid;

 		if (of_irq_parse_one(node, i, &parent)) {
 			pr_err("failed to parse parent for context %d.\n", i);
 			continue;
 		}

 		/*
 		 * Skip contexts other than external interrupts for our
 		 * privilege level.
 		 */
 		if (parent.args[0] != RV_IRQ_EXT)
 			continue;

 		hartid = riscv_of_parent_hartid(parent.np);
 		if (hartid < 0) {
 			pr_warn("failed to parse hart ID for context %d.\n", i);
 			continue;
 		}

 		cpu = riscv_hartid_to_cpuid(hartid);
 		if (cpu < 0) {
 			pr_warn("Invalid cpuid for context %d\n", i);
 			continue;
 		}

 		/* Find parent domain and register chained handler */
 		if (!plic_parent_irq && irq_find_host(parent.np)) {
 			plic_parent_irq = irq_of_parse_and_map(node, i);
 			if (plic_parent_irq)
 				irq_set_chained_handler(plic_parent_irq,
 							plic_handle_irq);
 		}

 		/*
 		 * When running in M-mode we need to ignore the S-mode handler.
 		 * Here we assume it always comes later, but that might be a
 		 * little fragile.
 		 */
 		handler = per_cpu_ptr(&plic_handlers, cpu);
 		if (handler->present) {
 			pr_warn("handler already present for context %d.\n", i);
 			plic_set_threshold(handler, PLIC_DISABLE_THRESHOLD);
 			goto done;
 		}

 		cpumask_set_cpu(cpu, &priv->lmask);
 		handler->present = true;
 		handler->hart_base =
 			priv->regs + CONTEXT_BASE + i * CONTEXT_PER_HART;
 		raw_spin_lock_init(&handler->enable_lock);
 		handler->enable_base =
 			priv->regs + ENABLE_BASE + i * ENABLE_PER_HART;
 		handler->priv = priv;
 done:
 		for (hwirq = 1; hwirq <= nr_irqs; hwirq++)
 			plic_toggle(handler, hwirq, 0);
 		nr_handlers++;
 	}

 	/*
 	 * We can have multiple PLIC instances so setup cpuhp state only
 	 * when context handler for current/boot CPU is present.
 	 */
 	handler = this_cpu_ptr(&plic_handlers);
 	if (handler->present && !plic_cpuhp_setup_done) {
 		cpuhp_setup_state(CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
 				  "irqchip/sifive/plic:starting",
 				  plic_starting_cpu, plic_dying_cpu);
 		plic_cpuhp_setup_done = true;
 	}

 	pr_info("%pOFP: mapped %d interrupts with %d handlers for"
 		" %d contexts.\n", node, nr_irqs, nr_handlers, nr_contexts);
 	return 0;

 out_iounmap:
 	iounmap(priv->regs);
 out_free_priv:
 	kfree(priv);
 	return error;
 }

 IRQCHIP_DECLARE(sifive_plic, "sifive,plic-1.0.0", plic_init);
 IRQCHIP_DECLARE(riscv_plic0, "riscv,plic0", plic_init); /* for legacy systems */
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Copyright (C) 2017 SiFive
	* Copyright (C) 2018 Christoph Hellwig
	*/
	#define pr_fmt(fmt) "plic: " fmt
	#include <linux/cpu.h>
	#include <linux/interrupt.h>
	#include <linux/io.h>
	#include <linux/irq.h>
	#include <linux/irqchip.h>
	#include <linux/irqchip/chained_irq.h>
	#include <linux/irqdomain.h>
	#include <linux/module.h>
	#include <linux/of.h>
	#include <linux/of_address.h>
	#include <linux/of_irq.h>
	#include <linux/platform_device.h>
	#include <linux/spinlock.h>
	#include <asm/smp.h>

	/*
	* This driver implements a version of the RISC-V PLIC with the actual layout
	* specified in chapter 8 of the SiFive U5 Coreplex Series Manual:
	*
	* https://static.dev.sifive.com/U54-MC-RVCoreIP.pdf
	*
	* The largest number supported by devices marked as 'sifive,plic-1.0.0', is
	* 1024, of which device 0 is defined as non-existent by the RISC-V Privileged
	* Spec.
	*/

	#define MAX_DEVICES 1024
	#define MAX_CONTEXTS 15872

	/*
	* Each interrupt source has a priority register associated with it.
	* We always hardwire it to one in Linux.
	*/
	#define PRIORITY_BASE 0
	#define PRIORITY_PER_ID 4

	/*
	* Each hart context has a vector of interrupt enable bits associated with it.
	* There's one bit for each interrupt source.
	*/
	#define ENABLE_BASE 0x2000
	#define ENABLE_PER_HART 0x80

	/*
	* Each hart context has a set of control registers associated with it. Right
	* now there's only two: a source priority threshold over which the hart will
	* take an interrupt, and a register to claim interrupts.
	*/
	#define CONTEXT_BASE 0x200000
	#define CONTEXT_PER_HART 0x1000
	#define CONTEXT_THRESHOLD 0x00
	#define CONTEXT_CLAIM 0x04

	#define PLIC_DISABLE_THRESHOLD 0x7
	#define PLIC_ENABLE_THRESHOLD 0

	struct plic_priv {
	struct cpumask lmask;
	struct irq_domain *irqdomain;
	void __iomem *regs;
	};

	struct plic_handler {
	bool present;
	void __iomem *hart_base;
	/*
	* Protect mask operations on the registers given that we can't
	* assume atomic memory operations work on them.
	*/
	raw_spinlock_t enable_lock;
	void __iomem *enable_base;
	struct plic_priv *priv;
	};
	static int plic_parent_irq __ro_after_init;
	static bool plic_cpuhp_setup_done __ro_after_init;
	static DEFINE_PER_CPU(struct plic_handler, plic_handlers);

	static inline void plic_toggle(struct plic_handler *handler,
	int hwirq, int enable)
	{
	u32 __iomem reg = handler->enable_base + (hwirq / 32) sizeof(u32);
	u32 hwirq_mask = 1 << (hwirq % 32);

	raw_spin_lock(&handler->enable_lock);
	if (enable)
	writel(readl(reg) \| hwirq_mask, reg);
	else
	writel(readl(reg) & ~hwirq_mask, reg);
	raw_spin_unlock(&handler->enable_lock);
	}

	static inline void plic_irq_toggle(const struct cpumask *mask,
	struct irq_data *d, int enable)
	{
	int cpu;
	struct plic_priv *priv = irq_data_get_irq_chip_data(d);

	writel(enable, priv->regs + PRIORITY_BASE + d->hwirq * PRIORITY_PER_ID);
	for_each_cpu(cpu, mask) {
	struct plic_handler *handler = per_cpu_ptr(&plic_handlers, cpu);

	if (handler->present &&
	cpumask_test_cpu(cpu, &handler->priv->lmask))
	plic_toggle(handler, d->hwirq, enable);
	}
	}

	static void plic_irq_unmask(struct irq_data *d)
	{
	struct cpumask amask;
	unsigned int cpu;
	struct plic_priv *priv = irq_data_get_irq_chip_data(d);

	cpumask_and(&amask, &priv->lmask, cpu_online_mask);
	cpu = cpumask_any_and(irq_data_get_affinity_mask(d),
	&amask);
	if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
	return;
	plic_irq_toggle(cpumask_of(cpu), d, 1);
	}

	static void plic_irq_mask(struct irq_data *d)
	{
	struct plic_priv *priv = irq_data_get_irq_chip_data(d);

	plic_irq_toggle(&priv->lmask, d, 0);
	}

	#ifdef CONFIG_SMP
	static int plic_set_affinity(struct irq_data *d,
	const struct cpumask *mask_val, bool force)
	{
	unsigned int cpu;
	struct cpumask amask;
	struct plic_priv *priv = irq_data_get_irq_chip_data(d);

	cpumask_and(&amask, &priv->lmask, mask_val);

	if (force)
	cpu = cpumask_first(&amask);
	else
	cpu = cpumask_any_and(&amask, cpu_online_mask);

	if (cpu >= nr_cpu_ids)
	return -EINVAL;

	plic_irq_toggle(&priv->lmask, d, 0);
	plic_irq_toggle(cpumask_of(cpu), d, !irqd_irq_masked(d));

	irq_data_update_effective_affinity(d, cpumask_of(cpu));

	return IRQ_SET_MASK_OK_DONE;
	}
	#endif

	static void plic_irq_eoi(struct irq_data *d)
	{
	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);

	writel(d->hwirq, handler->hart_base + CONTEXT_CLAIM);
	}

	static struct irq_chip plic_chip = {
	.name = "SiFive PLIC",
	.irq_mask = plic_irq_mask,
	.irq_unmask = plic_irq_unmask,
	.irq_eoi = plic_irq_eoi,
	#ifdef CONFIG_SMP
	.irq_set_affinity = plic_set_affinity,
	#endif
	};

	static int plic_irqdomain_map(struct irq_domain *d, unsigned int irq,
	irq_hw_number_t hwirq)
	{
	struct plic_priv *priv = d->host_data;

	irq_domain_set_info(d, irq, hwirq, &plic_chip, d->host_data,
	handle_fasteoi_irq, NULL, NULL);
	irq_set_noprobe(irq);
	irq_set_affinity(irq, &priv->lmask);
	return 0;
	}

	static int plic_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
	unsigned int nr_irqs, void *arg)
	{
	int i, ret;
	irq_hw_number_t hwirq;
	unsigned int type;
	struct irq_fwspec *fwspec = arg;

	ret = irq_domain_translate_onecell(domain, fwspec, &hwirq, &type);
	if (ret)
	return ret;

	for (i = 0; i < nr_irqs; i++) {
	ret = plic_irqdomain_map(domain, virq + i, hwirq + i);
	if (ret)
	return ret;
	}

	return 0;
	}

	static const struct irq_domain_ops plic_irqdomain_ops = {
	.translate = irq_domain_translate_onecell,
	.alloc = plic_irq_domain_alloc,
	.free = irq_domain_free_irqs_top,
	};

	/*
	* Handling an interrupt is a two-step process: first you claim the interrupt
	* by reading the claim register, then you complete the interrupt by writing
	* that source ID back to the same claim register. This automatically enables
	* and disables the interrupt, so there's nothing else to do.
	*/
	static void plic_handle_irq(struct irq_desc *desc)
	{
	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
	struct irq_chip *chip = irq_desc_get_chip(desc);
	void __iomem *claim = handler->hart_base + CONTEXT_CLAIM;
	irq_hw_number_t hwirq;

	WARN_ON_ONCE(!handler->present);

	chained_irq_enter(chip, desc);

	while ((hwirq = readl(claim))) {
	int irq = irq_find_mapping(handler->priv->irqdomain, hwirq);

	if (unlikely(irq <= 0))
	pr_warn_ratelimited("can't find mapping for hwirq %lu\n",
	hwirq);
	else
	generic_handle_irq(irq);
	}

	chained_irq_exit(chip, desc);
	}

	static void plic_set_threshold(struct plic_handler *handler, u32 threshold)
	{
	/* priority must be > threshold to trigger an interrupt */
	writel(threshold, handler->hart_base + CONTEXT_THRESHOLD);
	}

	static int plic_dying_cpu(unsigned int cpu)
	{
	if (plic_parent_irq)
	disable_percpu_irq(plic_parent_irq);

	return 0;
	}

	static int plic_starting_cpu(unsigned int cpu)
	{
	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);

	if (plic_parent_irq)
	enable_percpu_irq(plic_parent_irq,
	irq_get_trigger_type(plic_parent_irq));
	else
	pr_warn("cpu%d: parent irq not available\n", cpu);
	plic_set_threshold(handler, PLIC_ENABLE_THRESHOLD);

	return 0;
	}

	static int __init plic_init(struct device_node *node,
	struct device_node *parent)
	{
	int error = 0, nr_contexts, nr_handlers = 0, i;
	u32 nr_irqs;
	struct plic_priv *priv;
	struct plic_handler *handler;

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv)
	return -ENOMEM;

	priv->regs = of_iomap(node, 0);
	if (WARN_ON(!priv->regs)) {
	error = -EIO;
	goto out_free_priv;
	}

	error = -EINVAL;
	of_property_read_u32(node, "riscv,ndev", &nr_irqs);
	if (WARN_ON(!nr_irqs))
	goto out_iounmap;

	nr_contexts = of_irq_count(node);
	if (WARN_ON(!nr_contexts))
	goto out_iounmap;

	error = -ENOMEM;
	priv->irqdomain = irq_domain_add_linear(node, nr_irqs + 1,
	&plic_irqdomain_ops, priv);
	if (WARN_ON(!priv->irqdomain))
	goto out_iounmap;

	for (i = 0; i < nr_contexts; i++) {
	struct of_phandle_args parent;
	irq_hw_number_t hwirq;
	int cpu, hartid;

	if (of_irq_parse_one(node, i, &parent)) {
	pr_err("failed to parse parent for context %d.\n", i);
	continue;
	}

	/*
	* Skip contexts other than external interrupts for our
	* privilege level.
	*/
	if (parent.args[0] != RV_IRQ_EXT)
	continue;

	hartid = riscv_of_parent_hartid(parent.np);
	if (hartid < 0) {
	pr_warn("failed to parse hart ID for context %d.\n", i);
	continue;
	}

	cpu = riscv_hartid_to_cpuid(hartid);
	if (cpu < 0) {
	pr_warn("Invalid cpuid for context %d\n", i);
	continue;
	}

	/* Find parent domain and register chained handler */
	if (!plic_parent_irq && irq_find_host(parent.np)) {
	plic_parent_irq = irq_of_parse_and_map(node, i);
	if (plic_parent_irq)
	irq_set_chained_handler(plic_parent_irq,
	plic_handle_irq);
	}

	/*
	* When running in M-mode we need to ignore the S-mode handler.
	* Here we assume it always comes later, but that might be a
	* little fragile.
	*/
	handler = per_cpu_ptr(&plic_handlers, cpu);
	if (handler->present) {
	pr_warn("handler already present for context %d.\n", i);
	plic_set_threshold(handler, PLIC_DISABLE_THRESHOLD);
	goto done;
	}

	cpumask_set_cpu(cpu, &priv->lmask);
	handler->present = true;
	handler->hart_base =
	priv->regs + CONTEXT_BASE + i * CONTEXT_PER_HART;
	raw_spin_lock_init(&handler->enable_lock);
	handler->enable_base =
	priv->regs + ENABLE_BASE + i * ENABLE_PER_HART;
	handler->priv = priv;
	done:
	for (hwirq = 1; hwirq <= nr_irqs; hwirq++)
	plic_toggle(handler, hwirq, 0);
	nr_handlers++;
	}

	/*
	* We can have multiple PLIC instances so setup cpuhp state only
	* when context handler for current/boot CPU is present.
	*/
	handler = this_cpu_ptr(&plic_handlers);
	if (handler->present && !plic_cpuhp_setup_done) {
	cpuhp_setup_state(CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
	"irqchip/sifive/plic:starting",
	plic_starting_cpu, plic_dying_cpu);
	plic_cpuhp_setup_done = true;
	}

	pr_info("%pOFP: mapped %d interrupts with %d handlers for"
	" %d contexts.\n", node, nr_irqs, nr_handlers, nr_contexts);
	return 0;

	out_iounmap:
	iounmap(priv->regs);
	out_free_priv:
	kfree(priv);
	return error;
	}

	IRQCHIP_DECLARE(sifive_plic, "sifive,plic-1.0.0", plic_init);
	IRQCHIP_DECLARE(riscv_plic0, "riscv,plic0", plic_init); /* for legacy systems */