irqchip: RISC-V per-HART local interrupt controller driver

The RISC-V per-HART local interrupt controller manages software
interrupts, timer interrupts, external interrupts (which are routed
via the platform level interrupt controller) and other per-HART
local interrupts.

We add a driver for the RISC-V local interrupt controller, which
eventually replaces the RISC-V architecture code, allowing for a
better split between arch code and drivers.

The driver is compliant with RISC-V Hart-Level Interrupt Controller
DT bindings located at:
Documentation/devicetree/bindings/interrupt-controller/riscv,cpu-intc.txt

Co-developed-by: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
[Palmer: Cleaned up warnings]
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

arch/riscv/Kconfig

@@ -40,6 +40,7 @@ config RISCV
 	select GENERIC_SMP_IDLE_THREAD
 	select GENERIC_STRNCPY_FROM_USER if MMU
 	select GENERIC_STRNLEN_USER if MMU
+	select HANDLE_DOMAIN_IRQ
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_KASAN if MMU && 64BIT
 	select HAVE_ARCH_KGDB

arch/riscv/include/asm/irq.h

@@ -10,8 +10,6 @@
 #include <linux/interrupt.h>
 #include <linux/linkage.h>
 
-#define NR_IRQS         0
-
 void riscv_timer_interrupt(void);
 
 #include <asm-generic/irq.h>

arch/riscv/kernel/irq.c

@@ -7,7 +7,6 @@
 
 #include <linux/interrupt.h>
 #include <linux/irqchip.h>
-#include <linux/irqdomain.h>
 #include <linux/seq_file.h>
 #include <asm/smp.h>
 
@@ -19,39 +18,13 @@ int arch_show_interrupts(struct seq_file *p, int prec)
 
 asmlinkage __visible void __irq_entry do_IRQ(struct pt_regs *regs)
 {
-	struct pt_regs *old_regs;
-
-	switch (regs->cause & ~CAUSE_IRQ_FLAG) {
-	case RV_IRQ_TIMER:
-		old_regs = set_irq_regs(regs);
-		irq_enter();
-		riscv_timer_interrupt();
-		irq_exit();
-		set_irq_regs(old_regs);
-		break;
-#ifdef CONFIG_SMP
-	case RV_IRQ_SOFT:
-		/*
-		 * We only use software interrupts to pass IPIs, so if a non-SMP
-		 * system gets one, then we don't know what to do.
-		 */
-		handle_IPI(regs);
-		break;
-#endif
-	case RV_IRQ_EXT:
-		old_regs = set_irq_regs(regs);
-		irq_enter();
+	if (handle_arch_irq)
 		handle_arch_irq(regs);
-		irq_exit();
-		set_irq_regs(old_regs);
-		break;
-	default:
-		pr_alert("unexpected interrupt cause 0x%lx", regs->cause);
-		BUG();
-	}
 }
 
 void __init init_IRQ(void)
 {
 	irqchip_init();
+	if (!handle_arch_irq)
+		panic("No interrupt controller found.");
 }

arch/riscv/kernel/traps.c

@@ -183,6 +183,4 @@ void trap_init(void)
 	csr_write(CSR_SCRATCH, 0);
 	/* Set the exception vector address */
 	csr_write(CSR_TVEC, &handle_exception);
-	/* Enable interrupts */
-	csr_write(CSR_IE, IE_SIE);
 }

drivers/irqchip/Kconfig

@@ -493,6 +493,19 @@ config TI_SCI_INTA_IRQCHIP
 	  If you wish to use interrupt aggregator irq resources managed by the
 	  TI System Controller, say Y here. Otherwise, say N.
 
+config RISCV_INTC
+	bool "RISC-V Local Interrupt Controller"
+	depends on RISCV
+	default y
+	help
+	   This enables support for the per-HART local interrupt controller
+	   found in standard RISC-V systems.  The per-HART local interrupt
+	   controller handles timer interrupts, software interrupts, and
+	   hardware interrupts. Without a per-HART local interrupt controller,
+	   a RISC-V system will be unable to handle any interrupts.
+
+	   If you don't know what to do here, say Y.
+
 config SIFIVE_PLIC
 	bool "SiFive Platform-Level Interrupt Controller"
 	depends on RISCV

drivers/irqchip/Makefile

@@ -98,6 +98,7 @@ obj-$(CONFIG_NDS32)			+= irq-ativic32.o
 obj-$(CONFIG_QCOM_PDC)			+= qcom-pdc.o
 obj-$(CONFIG_CSKY_MPINTC)		+= irq-csky-mpintc.o
 obj-$(CONFIG_CSKY_APB_INTC)		+= irq-csky-apb-intc.o
+obj-$(CONFIG_RISCV_INTC)		+= irq-riscv-intc.o
 obj-$(CONFIG_SIFIVE_PLIC)		+= irq-sifive-plic.o
 obj-$(CONFIG_IMX_IRQSTEER)		+= irq-imx-irqsteer.o
 obj-$(CONFIG_IMX_INTMUX)		+= irq-imx-intmux.o

drivers/irqchip/irq-riscv-intc.c

@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2012 Regents of the University of California
+ * Copyright (C) 2017-2018 SiFive
+ * Copyright (C) 2020 Western Digital Corporation or its affiliates.
+ */
+
+#define pr_fmt(fmt) "riscv-intc: " fmt
+#include <linux/atomic.h>
+#include <linux/bits.h>
+#include <linux/cpu.h>
+#include <linux/irq.h>
+#include <linux/irqchip.h>
+#include <linux/irqdomain.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/smp.h>
+
+static struct irq_domain *intc_domain;
+
+static asmlinkage void riscv_intc_irq(struct pt_regs *regs)
+{
+	struct pt_regs *old_regs;
+	unsigned long cause = regs->cause & ~CAUSE_IRQ_FLAG;
+
+	if (unlikely(cause >= BITS_PER_LONG))
+		panic("unexpected interrupt cause");
+
+	switch (cause) {
+	case RV_IRQ_TIMER:
+		old_regs = set_irq_regs(regs);
+		irq_enter();
+		riscv_timer_interrupt();
+		irq_exit();
+		set_irq_regs(old_regs);
+		break;
+#ifdef CONFIG_SMP
+	case RV_IRQ_SOFT:
+		/*
+		 * We only use software interrupts to pass IPIs, so if a
+		 * non-SMP system gets one, then we don't know what to do.
+		 */
+		handle_IPI(regs);
+		break;
+#endif
+	default:
+		handle_domain_irq(intc_domain, cause, regs);
+		break;
+	}
+}
+
+/*
+ * On RISC-V systems local interrupts are masked or unmasked by writing
+ * the SIE (Supervisor Interrupt Enable) CSR.  As CSRs can only be written
+ * on the local hart, these functions can only be called on the hart that
+ * corresponds to the IRQ chip.
+ */
+
+static void riscv_intc_irq_mask(struct irq_data *d)
+{
+	csr_clear(CSR_IE, BIT(d->hwirq));
+}
+
+static void riscv_intc_irq_unmask(struct irq_data *d)
+{
+	csr_set(CSR_IE, BIT(d->hwirq));
+}
+
+static int riscv_intc_cpu_starting(unsigned int cpu)
+{
+	csr_set(CSR_IE, BIT(RV_IRQ_SOFT));
+	return 0;
+}
+
+static int riscv_intc_cpu_dying(unsigned int cpu)
+{
+	csr_clear(CSR_IE, BIT(RV_IRQ_SOFT));
+	return 0;
+}
+
+static struct irq_chip riscv_intc_chip = {
+	.name = "RISC-V INTC",
+	.irq_mask = riscv_intc_irq_mask,
+	.irq_unmask = riscv_intc_irq_unmask,
+};
+
+static int riscv_intc_domain_map(struct irq_domain *d, unsigned int irq,
+				 irq_hw_number_t hwirq)
+{
+	irq_set_percpu_devid(irq);
+	irq_domain_set_info(d, irq, hwirq, &riscv_intc_chip, d->host_data,
+			    handle_percpu_devid_irq, NULL, NULL);
+
+	return 0;
+}
+
+static const struct irq_domain_ops riscv_intc_domain_ops = {
+	.map	= riscv_intc_domain_map,
+	.xlate	= irq_domain_xlate_onecell,
+};
+
+static int __init riscv_intc_init(struct device_node *node,
+				  struct device_node *parent)
+{
+	int rc, hartid;
+
+	hartid = riscv_of_parent_hartid(node);
+	if (hartid < 0) {
+		pr_warn("unable to fine hart id for %pOF\n", node);
+		return 0;
+	}
+
+	/*
+	 * The DT will have one INTC DT node under each CPU (or HART)
+	 * DT node so riscv_intc_init() function will be called once
+	 * for each INTC DT node. We only need to do INTC initialization
+	 * for the INTC DT node belonging to boot CPU (or boot HART).
+	 */
+	if (riscv_hartid_to_cpuid(hartid) != smp_processor_id())
+		return 0;
+
+	intc_domain = irq_domain_add_linear(node, BITS_PER_LONG,
+					    &riscv_intc_domain_ops, NULL);
+	if (!intc_domain) {
+		pr_err("unable to add IRQ domain\n");
+		return -ENXIO;
+	}
+
+	rc = set_handle_irq(&riscv_intc_irq);
+	if (rc) {
+		pr_err("failed to set irq handler\n");
+		return rc;
+	}
+
+	cpuhp_setup_state(CPUHP_AP_IRQ_RISCV_STARTING,
+			  "irqchip/riscv/intc:starting",
+			  riscv_intc_cpu_starting,
+			  riscv_intc_cpu_dying);
+
+	pr_info("%d local interrupts mapped\n", BITS_PER_LONG);
+
+	return 0;
+}
+
+IRQCHIP_DECLARE(riscv, "riscv,cpu-intc", riscv_intc_init);

drivers/irqchip/irq-sifive-plic.c

@@ -9,6 +9,7 @@
 #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>
@@ -76,6 +77,7 @@ struct plic_handler {
 	void __iomem		*enable_base;
 	struct plic_priv	*priv;
 };
+static int plic_parent_irq;
 static bool plic_cpuhp_setup_done;
 static DEFINE_PER_CPU(struct plic_handler, plic_handlers);
 
@@ -219,15 +221,17 @@ static const struct irq_domain_ops plic_irqdomain_ops = {
  * 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 pt_regs *regs)
+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);
 
-	csr_clear(CSR_IE, IE_EIE);
+	chained_irq_enter(chip, desc);
+
 	while ((hwirq = readl(claim))) {
 		int irq = irq_find_mapping(handler->priv->irqdomain, hwirq);
 
@@ -237,7 +241,8 @@ static void plic_handle_irq(struct pt_regs *regs)
 		else
 			generic_handle_irq(irq);
 	}
-	csr_set(CSR_IE, IE_EIE);
+
+	chained_irq_exit(chip, desc);
 }
 
 static void plic_set_threshold(struct plic_handler *handler, u32 threshold)
@@ -248,10 +253,8 @@ static void plic_set_threshold(struct plic_handler *handler, u32 threshold)
 
 static int plic_dying_cpu(unsigned int cpu)
 {
-	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
-
-	csr_clear(CSR_IE, IE_EIE);
-	plic_set_threshold(handler, PLIC_DISABLE_THRESHOLD);
+	if (plic_parent_irq)
+		disable_percpu_irq(plic_parent_irq);
 
 	return 0;
 }
@@ -260,7 +263,11 @@ static int plic_starting_cpu(unsigned int cpu)
 {
 	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
 
-	csr_set(CSR_IE, IE_EIE);
+	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;
@@ -328,6 +335,14 @@ static int __init plic_init(struct device_node *node,
 			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
@@ -368,7 +383,6 @@ done:
 
 	pr_info("%pOFP: mapped %d interrupts with %d handlers for"
 		" %d contexts.\n", node, nr_irqs, nr_handlers, nr_contexts);
-	set_handle_irq(plic_handle_irq);
 	return 0;
 
 out_iounmap:

include/linux/cpuhotplug.h

@@ -102,6 +102,7 @@ enum cpuhp_state {
 	CPUHP_AP_IRQ_ARMADA_XP_STARTING,
 	CPUHP_AP_IRQ_BCM2836_STARTING,
 	CPUHP_AP_IRQ_MIPS_GIC_STARTING,
+	CPUHP_AP_IRQ_RISCV_STARTING,
 	CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
 	CPUHP_AP_ARM_MVEBU_COHERENCY,
 	CPUHP_AP_MICROCODE_LOADER,