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Subject[RFC PATCH 4/5] irqchip: RISC-V Local Interrupt Controller Driver
Date
The RISC-V local interrupt controller manages software interrupts,
timer interrupts, external interrupts (which are routed via the
platform level interrupt controller) and per-HART local interrupts.

This patch add a driver for RISC-V local interrupt controller. It's
a major re-write over perviously submitted version.
(Refer, https://www.spinics.net/lists/devicetree/msg241230.html)

Few advantages of this new driver over previous one are:
1. It registers all local interrupts as per-CPU interrupts
2. We can develop drivers for devices with per-CPU local interrupts
without changing arch code or this driver
3. It allows local interrupt controller DT node under each CPU DT node
as well as single system-wide DT node for local interrupt controller.

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

Signed-off-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
---
arch/riscv/include/asm/irq.h | 15 ++-
arch/riscv/kernel/irq.c | 59 +----------
drivers/irqchip/Kconfig | 15 ++-
drivers/irqchip/Makefile | 1 +
drivers/irqchip/irq-riscv-intc.c | 164 ++++++++++++++++++++++++++++++
drivers/irqchip/irq-sifive-plic.c | 21 +++-
include/linux/cpuhotplug.h | 1 +
7 files changed, 214 insertions(+), 62 deletions(-)
create mode 100644 drivers/irqchip/irq-riscv-intc.c

diff --git a/arch/riscv/include/asm/irq.h b/arch/riscv/include/asm/irq.h
index 93eb75eac4ff..fe503d71876a 100644
--- a/arch/riscv/include/asm/irq.h
+++ b/arch/riscv/include/asm/irq.h
@@ -15,7 +15,20 @@
#ifndef _ASM_RISCV_IRQ_H
#define _ASM_RISCV_IRQ_H

-#define NR_IRQS 0
+/*
+ * Possible interrupt causes:
+ */
+#define INTERRUPT_CAUSE_SOFTWARE 1
+#define INTERRUPT_CAUSE_TIMER 5
+#define INTERRUPT_CAUSE_EXTERNAL 9
+
+/*
+ * The high order bit of the trap cause register is always set for
+ * interrupts, which allows us to differentiate them from exceptions
+ * quickly. The INTERRUPT_CAUSE_* macros don't contain that bit, so we
+ * need to mask it off.
+ */
+#define INTERRUPT_CAUSE_FLAG (1UL << (__riscv_xlen - 1))

void riscv_timer_interrupt(void);

diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
index c51c9b402e87..46a311e5f0f6 100644
--- a/arch/riscv/kernel/irq.c
+++ b/arch/riscv/kernel/irq.c
@@ -7,69 +7,16 @@

#include <linux/interrupt.h>
#include <linux/irqchip.h>
-#include <linux/irqdomain.h>
-
-#include <asm/sbi.h>
-
-/*
- * Possible interrupt causes:
- */
-#define INTERRUPT_CAUSE_SOFTWARE 1
-#define INTERRUPT_CAUSE_TIMER 5
-#define INTERRUPT_CAUSE_EXTERNAL 9
-
-/*
- * The high order bit of the trap cause register is always set for
- * interrupts, which allows us to differentiate them from exceptions
- * quickly. The INTERRUPT_CAUSE_* macros don't contain that bit, so we
- * need to mask it off.
- */
-#define INTERRUPT_CAUSE_FLAG (1UL << (__riscv_xlen - 1))

asmlinkage void __irq_entry do_IRQ(struct pt_regs *regs)
{
- struct pt_regs *old_regs;
-
- switch (regs->scause & ~INTERRUPT_CAUSE_FLAG) {
- case INTERRUPT_CAUSE_TIMER:
- old_regs = set_irq_regs(regs);
- irq_enter();
- riscv_timer_interrupt();
- irq_exit();
- set_irq_regs(old_regs);
- break;
-#ifdef CONFIG_SMP
- case INTERRUPT_CAUSE_SOFTWARE:
- /*
- * 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 INTERRUPT_CAUSE_EXTERNAL:
- 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:
- panic("unexpected interrupt cause");
- }
-}
-
-#ifdef CONFIG_SMP
-static void smp_ipi_trigger_sbi(const struct cpumask *to_whom)
-{
- sbi_send_ipi(cpumask_bits(to_whom));
}
-#endif

void __init init_IRQ(void)
{
irqchip_init();
-#ifdef CONFIG_SMP
- set_smp_ipi_trigger(smp_ipi_trigger_sbi);
-#endif
+ if (!handle_arch_irq)
+ panic("No interrupt controller found.");
}
diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
index 383e7b70221d..885e182586f4 100644
--- a/drivers/irqchip/Kconfig
+++ b/drivers/irqchip/Kconfig
@@ -371,7 +371,18 @@ config QCOM_PDC
Power Domain Controller driver to manage and configure wakeup
IRQs for Qualcomm Technologies Inc (QTI) mobile chips.

-endmenu
+config RISCV_INTC
+ bool "RISC-V Interrupt Controller"
+ depends on RISCV
+ default y
+ help
+ This enables support for the local interrupt controller found in
+ standard RISC-V systems. The local interrupt controller handles
+ timer interrupts, software interrupts, and hardware interrupts.
+ Without a local interrupt controller the system will be unable to
+ handle any interrupts, including those passed via the PLIC.
+
+ If you don't know what to do here, say Y.

config SIFIVE_PLIC
bool "SiFive Platform-Level Interrupt Controller"
@@ -384,3 +395,5 @@ config SIFIVE_PLIC
interrupt sources are subordinate to the PLIC.

If you don't know what to do here, say Y.
+
+endmenu
diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
index fbd1ec8070ef..e638ee5c4452 100644
--- a/drivers/irqchip/Makefile
+++ b/drivers/irqchip/Makefile
@@ -87,4 +87,5 @@ obj-$(CONFIG_MESON_IRQ_GPIO) += irq-meson-gpio.o
obj-$(CONFIG_GOLDFISH_PIC) += irq-goldfish-pic.o
obj-$(CONFIG_NDS32) += irq-ativic32.o
obj-$(CONFIG_QCOM_PDC) += qcom-pdc.o
+obj-$(CONFIG_RISCV_INTC) += irq-riscv-intc.o
obj-$(CONFIG_SIFIVE_PLIC) += irq-sifive-plic.o
diff --git a/drivers/irqchip/irq-riscv-intc.c b/drivers/irqchip/irq-riscv-intc.c
new file mode 100644
index 000000000000..c80502a1e12b
--- /dev/null
+++ b/drivers/irqchip/irq-riscv-intc.c
@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2012 Regents of the University of California
+ * Copyright (C) 2017-2018 SiFive
+ * Copyright (C) 2018 Anup Patel
+ */
+
+#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/of.h>
+#include <linux/smp.h>
+#include <asm/sbi.h>
+
+static struct irq_domain *intc_domain;
+static atomic_t intc_init = ATOMIC_INIT(0);
+
+static void riscv_intc_irq(struct pt_regs *regs)
+{
+ struct pt_regs *old_regs;
+ unsigned long cause = regs->scause & ~INTERRUPT_CAUSE_FLAG;
+
+ if (unlikely(cause >= BITS_PER_LONG))
+ panic("unexpected interrupt cause");
+
+ switch (cause) {
+ case INTERRUPT_CAUSE_TIMER:
+ old_regs = set_irq_regs(regs);
+ irq_enter();
+ riscv_timer_interrupt();
+ irq_exit();
+ set_irq_regs(old_regs);
+ break;
+#ifdef CONFIG_SMP
+ case INTERRUPT_CAUSE_SOFTWARE:
+ /*
+ * 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. They are only called internally to this module, so they BUG_ON if
+ * this condition is violated rather than attempting to handle the error by
+ * forwarding to the target hart, as that's already expected to have been done.
+ */
+static void riscv_intc_irq_mask(struct irq_data *d)
+{
+ csr_clear(sie, 1 << (long)d->hwirq);
+}
+
+static void riscv_intc_irq_unmask(struct irq_data *d)
+{
+ csr_set(sie, 1 << (long)d->hwirq);
+}
+
+#ifdef CONFIG_SMP
+static void riscv_intc_ipi_trigger(const struct cpumask *to_whom)
+{
+ sbi_send_ipi(cpumask_bits(to_whom));
+}
+
+static int riscv_intc_cpu_starting(unsigned int cpu)
+{
+ csr_set(sie, 1 << INTERRUPT_CAUSE_SOFTWARE);
+ return 0;
+}
+
+static int riscv_intc_cpu_dying(unsigned int cpu)
+{
+ csr_clear(sie, 1 << INTERRUPT_CAUSE_SOFTWARE);
+ return 0;
+}
+
+static void riscv_intc_smp_init(void)
+{
+ csr_write(sie, 0);
+ csr_write(sip, 0);
+
+ set_smp_ipi_trigger(riscv_intc_ipi_trigger);
+
+ cpuhp_setup_state(CPUHP_AP_IRQ_RISCV_STARTING,
+ "irqchip/riscv/intc:starting",
+ riscv_intc_cpu_starting,
+ riscv_intc_cpu_dying);
+
+}
+#else
+static void riscv_intc_smp_init(void)
+{
+ csr_write(sie, 0);
+ csr_write(sip, 0);
+}
+#endif
+
+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);
+ irq_set_status_flags(irq, IRQ_NOAUTOEN);
+
+ 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)
+{
+ /*
+ * RISC-V device trees can have one INTC DT node under
+ * each CPU DT node so INTC init function will be called
+ * once for each INTC DT node. We only need to do INTC
+ * init once for boot CPU so we use atomic counter to
+ * achieve this.
+ */
+ if (atomic_inc_return(&intc_init) > 1)
+ return 0;
+
+ intc_domain = irq_domain_add_linear(node, BITS_PER_LONG,
+ &riscv_intc_domain_ops, NULL);
+ if (!intc_domain)
+ goto error_add_linear;
+
+ set_handle_irq(&riscv_intc_irq);
+
+ riscv_intc_smp_init();
+
+ pr_info("%lu local interrupts mapped\n", (long)BITS_PER_LONG);
+
+ return 0;
+
+error_add_linear:
+ pr_warn("unable to add IRQ domain\n");
+ return -ENXIO;
+}
+
+IRQCHIP_DECLARE(riscv, "riscv,cpu-intc", riscv_intc_init);
diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index 532e9d68c704..ab9614d5a2b4 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -8,6 +8,7 @@
#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>
@@ -146,14 +147,17 @@ static struct irq_domain *plic_irqdomain;
* 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 = plic_hart_offset(handler->ctxid) + CONTEXT_CLAIM;
irq_hw_number_t hwirq;

WARN_ON_ONCE(!handler->present);

+ chained_irq_enter(chip, desc);
+
csr_clear(sie, SIE_SEIE);
while ((hwirq = readl(claim))) {
int irq = irq_find_mapping(plic_irqdomain, hwirq);
@@ -166,6 +170,8 @@ static void plic_handle_irq(struct pt_regs *regs)
writel(hwirq, claim);
}
csr_set(sie, SIE_SEIE);
+
+ chained_irq_exit(chip, desc);
}

/*
@@ -183,7 +189,7 @@ static int plic_find_hart_id(struct device_node *node)
}

static int __init plic_init(struct device_node *node,
- struct device_node *parent)
+ struct device_node *parent)
{
int error = 0, nr_handlers, nr_mapped = 0, i;
u32 nr_irqs;
@@ -218,7 +224,7 @@ static int __init plic_init(struct device_node *node,
struct of_phandle_args parent;
struct plic_handler *handler;
irq_hw_number_t hwirq;
- int cpu;
+ int cpu, parent_irq;

if (of_irq_parse_one(node, i, &parent)) {
pr_err("failed to parse parent for context %d.\n", i);
@@ -229,6 +235,13 @@ static int __init plic_init(struct device_node *node,
if (parent.args[0] == -1)
continue;

+ if (irq_find_host(parent.np)) {
+ parent_irq = irq_of_parse_and_map(node, i);
+ if (parent_irq)
+ irq_set_chained_handler(parent_irq,
+ plic_handle_irq);
+ }
+
cpu = plic_find_hart_id(parent.np);
if (cpu < 0) {
pr_warn("failed to parse hart ID for context %d.\n", i);
@@ -248,7 +261,7 @@ static int __init plic_init(struct device_node *node,

pr_info("mapped %d interrupts to %d (out of %d) handlers.\n",
nr_irqs, nr_mapped, nr_handlers);
- set_handle_irq(plic_handle_irq);
+
return 0;

out_iounmap:
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index caf40ad0bbc6..ca7268a38cef 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -100,6 +100,7 @@ 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_ARM_MVEBU_COHERENCY,
CPUHP_AP_PERF_X86_AMD_UNCORE_STARTING,
CPUHP_AP_PERF_X86_STARTING,
--
2.17.1
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