irqchip: Add RISC-V incoming MSI controller early driver

The RISC-V advanced interrupt architecture (AIA) specification
defines a new MSI controller called incoming message signalled
interrupt controller (IMSIC) which manages MSI on per-HART (or
per-CPU) basis. It also supports IPIs as software injected MSIs.
(For more details refer https://github.com/riscv/riscv-aia)

Add an early irqchip driver for RISC-V IMSIC which sets up the
IMSIC state and provide IPIs.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20240307140307.646078-3-apatel@ventanamicro.com

drivers/irqchip/Kconfig

@@ -540,6 +540,13 @@ config RISCV_INTC
 	depends on RISCV
 	select IRQ_DOMAIN_HIERARCHY
 
+config RISCV_IMSIC
+	bool
+	depends on RISCV
+	select IRQ_DOMAIN_HIERARCHY
+	select GENERIC_IRQ_MATRIX_ALLOCATOR
+	select GENERIC_MSI_IRQ
+
 config SIFIVE_PLIC
 	bool
 	depends on RISCV

drivers/irqchip/Makefile

@@ -95,6 +95,7 @@ obj-$(CONFIG_QCOM_MPM)			+= irq-qcom-mpm.o
 obj-$(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-$(CONFIG_RISCV_IMSIC)		+= irq-riscv-imsic-state.o irq-riscv-imsic-early.o
 obj-$(CONFIG_SIFIVE_PLIC)		+= irq-sifive-plic.o
 obj-$(CONFIG_STARFIVE_JH8100_INTC)	+= irq-starfive-jh8100-intc.o
 obj-$(CONFIG_IMX_IRQSTEER)		+= irq-imx-irqsteer.o

drivers/irqchip/irq-riscv-imsic-early.c

@@ -0,0 +1,201 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 Western Digital Corporation or its affiliates.
+ * Copyright (C) 2022 Ventana Micro Systems Inc.
+ */
+
+#define pr_fmt(fmt) "riscv-imsic: " 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/module.h>
+#include <linux/spinlock.h>
+#include <linux/smp.h>
+
+#include "irq-riscv-imsic-state.h"
+
+static int imsic_parent_irq;
+
+#ifdef CONFIG_SMP
+static void imsic_ipi_send(unsigned int cpu)
+{
+	struct imsic_local_config *local = per_cpu_ptr(imsic->global.local, cpu);
+
+	writel_relaxed(IMSIC_IPI_ID, local->msi_va);
+}
+
+static void imsic_ipi_starting_cpu(void)
+{
+	/* Enable IPIs for current CPU. */
+	__imsic_id_set_enable(IMSIC_IPI_ID);
+}
+
+static void imsic_ipi_dying_cpu(void)
+{
+	/* Disable IPIs for current CPU. */
+	__imsic_id_clear_enable(IMSIC_IPI_ID);
+}
+
+static int __init imsic_ipi_domain_init(void)
+{
+	int virq;
+
+	/* Create IMSIC IPI multiplexing */
+	virq = ipi_mux_create(IMSIC_NR_IPI, imsic_ipi_send);
+	if (virq <= 0)
+		return virq < 0 ? virq : -ENOMEM;
+
+	/* Set vIRQ range */
+	riscv_ipi_set_virq_range(virq, IMSIC_NR_IPI, true);
+
+	/* Announce that IMSIC is providing IPIs */
+	pr_info("%pfwP: providing IPIs using interrupt %d\n", imsic->fwnode, IMSIC_IPI_ID);
+
+	return 0;
+}
+#else
+static void imsic_ipi_starting_cpu(void) { }
+static void imsic_ipi_dying_cpu(void) { }
+static int __init imsic_ipi_domain_init(void) { return 0; }
+#endif
+
+/*
+ * To handle an interrupt, we read the TOPEI CSR and write zero in one
+ * instruction. If TOPEI CSR is non-zero then we translate TOPEI.ID to
+ * Linux interrupt number and let Linux IRQ subsystem handle it.
+ */
+static void imsic_handle_irq(struct irq_desc *desc)
+{
+	struct irq_chip *chip = irq_desc_get_chip(desc);
+	int err, cpu = smp_processor_id();
+	struct imsic_vector *vec;
+	unsigned long local_id;
+
+	chained_irq_enter(chip, desc);
+
+	while ((local_id = csr_swap(CSR_TOPEI, 0))) {
+		local_id >>= TOPEI_ID_SHIFT;
+
+		if (local_id == IMSIC_IPI_ID) {
+			if (IS_ENABLED(CONFIG_SMP))
+				ipi_mux_process();
+			continue;
+		}
+
+		if (unlikely(!imsic->base_domain))
+			continue;
+
+		vec = imsic_vector_from_local_id(cpu, local_id);
+		if (!vec) {
+			pr_warn_ratelimited("vector not found for local ID 0x%lx\n", local_id);
+			continue;
+		}
+
+		err = generic_handle_domain_irq(imsic->base_domain, vec->hwirq);
+		if (unlikely(err))
+			pr_warn_ratelimited("hwirq 0x%x mapping not found\n", vec->hwirq);
+	}
+
+	chained_irq_exit(chip, desc);
+}
+
+static int imsic_starting_cpu(unsigned int cpu)
+{
+	/* Mark per-CPU IMSIC state as online */
+	imsic_state_online();
+
+	/* Enable per-CPU parent interrupt */
+	enable_percpu_irq(imsic_parent_irq, irq_get_trigger_type(imsic_parent_irq));
+
+	/* Setup IPIs */
+	imsic_ipi_starting_cpu();
+
+	/*
+	 * Interrupts identities might have been enabled/disabled while
+	 * this CPU was not running so sync-up local enable/disable state.
+	 */
+	imsic_local_sync_all();
+
+	/* Enable local interrupt delivery */
+	imsic_local_delivery(true);
+
+	return 0;
+}
+
+static int imsic_dying_cpu(unsigned int cpu)
+{
+	/* Cleanup IPIs */
+	imsic_ipi_dying_cpu();
+
+	/* Mark per-CPU IMSIC state as offline */
+	imsic_state_offline();
+
+	return 0;
+}
+
+static int __init imsic_early_probe(struct fwnode_handle *fwnode)
+{
+	struct irq_domain *domain;
+	int rc;
+
+	/* Find parent domain and register chained handler */
+	domain = irq_find_matching_fwnode(riscv_get_intc_hwnode(), DOMAIN_BUS_ANY);
+	if (!domain) {
+		pr_err("%pfwP: Failed to find INTC domain\n", fwnode);
+		return -ENOENT;
+	}
+	imsic_parent_irq = irq_create_mapping(domain, RV_IRQ_EXT);
+	if (!imsic_parent_irq) {
+		pr_err("%pfwP: Failed to create INTC mapping\n", fwnode);
+		return -ENOENT;
+	}
+
+	/* Initialize IPI domain */
+	rc = imsic_ipi_domain_init();
+	if (rc) {
+		pr_err("%pfwP: Failed to initialize IPI domain\n", fwnode);
+		return rc;
+	}
+
+	/* Setup chained handler to the parent domain interrupt */
+	irq_set_chained_handler(imsic_parent_irq, imsic_handle_irq);
+
+	/*
+	 * Setup cpuhp state (must be done after setting imsic_parent_irq)
+	 *
+	 * Don't disable per-CPU IMSIC file when CPU goes offline
+	 * because this affects IPI and the masking/unmasking of
+	 * virtual IPIs is done via generic IPI-Mux
+	 */
+	cpuhp_setup_state(CPUHP_AP_IRQ_RISCV_IMSIC_STARTING, "irqchip/riscv/imsic:starting",
+			  imsic_starting_cpu, imsic_dying_cpu);
+
+	return 0;
+}
+
+static int __init imsic_early_dt_init(struct device_node *node, struct device_node *parent)
+{
+	struct fwnode_handle *fwnode = &node->fwnode;
+	int rc;
+
+	/* Setup IMSIC state */
+	rc = imsic_setup_state(fwnode);
+	if (rc) {
+		pr_err("%pfwP: failed to setup state (error %d)\n", fwnode, rc);
+		return rc;
+	}
+
+	/* Do early setup of IPIs */
+	rc = imsic_early_probe(fwnode);
+	if (rc)
+		return rc;
+
+	/* Ensure that OF platform device gets probed */
+	of_node_clear_flag(node, OF_POPULATED);
+	return 0;
+}
+
+IRQCHIP_DECLARE(riscv_imsic, "riscv,imsics", imsic_early_dt_init);