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Subject[PATCH v11 3/7] genirq: Add mechanism to multiplex a single HW IPI
Date
All RISC-V platforms have a single HW IPI provided by the INTC local
interrupt controller. The HW method to trigger INTC IPI can be through
external irqchip (e.g. RISC-V AIA), through platform specific device
(e.g. SiFive CLINT timer), or through firmware (e.g. SBI IPI call).

To support multiple IPIs on RISC-V, we add a generic IPI multiplexing
mechanism which help us create multiple virtual IPIs using a single
HW IPI. This generic IPI multiplexing is inspired from the Apple AIC
irqchip driver and it is shared by various RISC-V irqchip drivers.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
---
include/linux/irq.h | 18 +++
kernel/irq/Kconfig | 5 +
kernel/irq/Makefile | 1 +
kernel/irq/ipi-mux.c | 268 +++++++++++++++++++++++++++++++++++++++++++
4 files changed, 292 insertions(+)
create mode 100644 kernel/irq/ipi-mux.c

diff --git a/include/linux/irq.h b/include/linux/irq.h
index c3eb89606c2b..5ab702cb0a5b 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -1266,6 +1266,24 @@ int __ipi_send_mask(struct irq_desc *desc, const struct cpumask *dest);
int ipi_send_single(unsigned int virq, unsigned int cpu);
int ipi_send_mask(unsigned int virq, const struct cpumask *dest);

+/**
+ * struct ipi_mux_ops - IPI multiplex operations
+ *
+ * @ipi_mux_pre_handle: Optional function called before handling parent IPI
+ * @ipi_mux_post_handle:Optional function called after handling parent IPI
+ * @ipi_mux_send: Trigger parent IPI on target CPUs
+ */
+struct ipi_mux_ops {
+ void (*ipi_mux_pre_handle)(unsigned int parent_virq, void *data);
+ void (*ipi_mux_post_handle)(unsigned int parent_virq, void *data);
+ void (*ipi_mux_send)(unsigned int parent_virq, void *data,
+ const struct cpumask *mask);
+};
+
+void ipi_mux_process(void);
+int ipi_mux_create(unsigned int parent_virq, unsigned int nr_ipi,
+ const struct ipi_mux_ops *ops, void *data);
+
#ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
/*
* Registers a generic IRQ handling function as the top-level IRQ handler in
diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
index db3d174c53d4..df17dbc54b02 100644
--- a/kernel/irq/Kconfig
+++ b/kernel/irq/Kconfig
@@ -86,6 +86,11 @@ config GENERIC_IRQ_IPI
depends on SMP
select IRQ_DOMAIN_HIERARCHY

+# Generic IRQ IPI Mux support
+config GENERIC_IRQ_IPI_MUX
+ bool
+ depends on SMP
+
# Generic MSI interrupt support
config GENERIC_MSI_IRQ
bool
diff --git a/kernel/irq/Makefile b/kernel/irq/Makefile
index b4f53717d143..f19d3080bf11 100644
--- a/kernel/irq/Makefile
+++ b/kernel/irq/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_GENERIC_IRQ_MIGRATION) += cpuhotplug.o
obj-$(CONFIG_PM_SLEEP) += pm.o
obj-$(CONFIG_GENERIC_MSI_IRQ) += msi.o
obj-$(CONFIG_GENERIC_IRQ_IPI) += ipi.o
+obj-$(CONFIG_GENERIC_IRQ_IPI_MUX) += ipi-mux.o
obj-$(CONFIG_SMP) += affinity.o
obj-$(CONFIG_GENERIC_IRQ_DEBUGFS) += debugfs.o
obj-$(CONFIG_GENERIC_IRQ_MATRIX_ALLOCATOR) += matrix.o
diff --git a/kernel/irq/ipi-mux.c b/kernel/irq/ipi-mux.c
new file mode 100644
index 000000000000..259e00366dd7
--- /dev/null
+++ b/kernel/irq/ipi-mux.c
@@ -0,0 +1,268 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Multiplex several virtual IPIs over a single HW IPI.
+ *
+ * Copyright The Asahi Linux Contributors
+ * Copyright (c) 2022 Ventana Micro Systems Inc.
+ */
+
+#define pr_fmt(fmt) "ipi-mux: " fmt
+#include <linux/cpu.h>
+#include <linux/init.h>
+#include <linux/irq.h>
+#include <linux/irqchip.h>
+#include <linux/irqchip/chained_irq.h>
+#include <linux/irqdomain.h>
+#include <linux/jump_label.h>
+#include <linux/percpu.h>
+#include <linux/smp.h>
+
+struct ipi_mux_cpu {
+ atomic_t enable;
+ atomic_t bits;
+ struct cpumask send_mask;
+};
+
+struct ipi_mux_control {
+ void *data;
+ unsigned int nr;
+ unsigned int parent_virq;
+ struct irq_domain *domain;
+ const struct ipi_mux_ops *ops;
+ struct ipi_mux_cpu __percpu *cpu;
+};
+
+static struct ipi_mux_control *imux;
+static DEFINE_STATIC_KEY_FALSE(imux_pre_handle);
+static DEFINE_STATIC_KEY_FALSE(imux_post_handle);
+
+static void ipi_mux_mask(struct irq_data *d)
+{
+ struct ipi_mux_cpu *icpu = this_cpu_ptr(imux->cpu);
+
+ atomic_andnot(BIT(irqd_to_hwirq(d)), &icpu->enable);
+}
+
+static void ipi_mux_unmask(struct irq_data *d)
+{
+ u32 ibit = BIT(irqd_to_hwirq(d));
+ struct ipi_mux_cpu *icpu = this_cpu_ptr(imux->cpu);
+
+ atomic_or(ibit, &icpu->enable);
+
+ /*
+ * The atomic_or() above must complete before the atomic_read()
+ * below to avoid racing ipi_mux_send_mask().
+ */
+ smp_mb__after_atomic();
+
+ /* If a pending IPI was unmasked, raise a parent IPI immediately. */
+ if (atomic_read(&icpu->bits) & ibit)
+ imux->ops->ipi_mux_send(imux->parent_virq, imux->data,
+ cpumask_of(smp_processor_id()));
+}
+
+static void ipi_mux_send_mask(struct irq_data *d, const struct cpumask *mask)
+{
+ u32 ibit = BIT(irqd_to_hwirq(d));
+ struct ipi_mux_cpu *icpu = this_cpu_ptr(imux->cpu);
+ struct cpumask *send_mask = &icpu->send_mask;
+ unsigned long flags;
+ int cpu;
+
+ /*
+ * We use send_mask as a per-CPU variable so disable local
+ * interrupts to avoid being preempted.
+ */
+ local_irq_save(flags);
+
+ cpumask_clear(send_mask);
+
+ for_each_cpu(cpu, mask) {
+ icpu = per_cpu_ptr(imux->cpu, cpu);
+ atomic_or(ibit, &icpu->bits);
+
+ /*
+ * The atomic_or() above must complete before
+ * the atomic_read() below to avoid racing with
+ * ipi_mux_unmask().
+ */
+ smp_mb__after_atomic();
+
+ if (atomic_read(&icpu->enable) & ibit)
+ cpumask_set_cpu(cpu, send_mask);
+ }
+
+ /* Trigger the parent IPI */
+ imux->ops->ipi_mux_send(imux->parent_virq, imux->data, send_mask);
+
+ local_irq_restore(flags);
+}
+
+static const struct irq_chip ipi_mux_chip = {
+ .name = "IPI Mux",
+ .irq_mask = ipi_mux_mask,
+ .irq_unmask = ipi_mux_unmask,
+ .ipi_send_mask = ipi_mux_send_mask,
+};
+
+static int ipi_mux_domain_alloc(struct irq_domain *d, unsigned int virq,
+ unsigned int nr_irqs, void *arg)
+{
+ int i;
+
+ for (i = 0; i < nr_irqs; i++) {
+ irq_set_percpu_devid(virq + i);
+ irq_domain_set_info(d, virq + i, i,
+ &ipi_mux_chip, d->host_data,
+ handle_percpu_devid_irq, NULL, NULL);
+ }
+
+ return 0;
+}
+
+static const struct irq_domain_ops ipi_mux_domain_ops = {
+ .alloc = ipi_mux_domain_alloc,
+ .free = irq_domain_free_irqs_top,
+};
+
+/**
+ * ipi_mux_process - Process multiplexed virtual IPIs
+ */
+void ipi_mux_process(void)
+{
+ struct ipi_mux_cpu *icpu = this_cpu_ptr(imux->cpu);
+ irq_hw_number_t hwirq;
+ unsigned long ipis;
+ int en;
+
+ if (static_branch_unlikely(&imux_pre_handle))
+ imux->ops->ipi_mux_pre_handle(imux->parent_virq, imux->data);
+
+ /*
+ * Reading enable mask does not need to be ordered as long as
+ * this function called from interrupt handler because only
+ * the CPU itself can change it's own enable mask.
+ */
+ en = atomic_read(&icpu->enable);
+
+ /*
+ * Clear the IPIs we are about to handle. This pairs with the
+ * atomic_fetch_or_release() in ipi_mux_send_mask().
+ */
+ ipis = atomic_fetch_andnot(en, &icpu->bits) & en;
+
+ for_each_set_bit(hwirq, &ipis, imux->nr)
+ generic_handle_domain_irq(imux->domain, hwirq);
+
+ if (static_branch_unlikely(&imux_post_handle))
+ imux->ops->ipi_mux_post_handle(imux->parent_virq, imux->data);
+}
+
+static void ipi_mux_handler(struct irq_desc *desc)
+{
+ struct irq_chip *chip = irq_desc_get_chip(desc);
+
+ chained_irq_enter(chip, desc);
+ ipi_mux_process();
+ chained_irq_exit(chip, desc);
+}
+
+/**
+ * ipi_mux_create - Create virtual IPIs multiplexed on top of a single
+ * parent IPI.
+ * @parent_virq: virq of the parent per-CPU IRQ
+ * @nr_ipi: number of virtual IPIs to create. This should
+ * be <= BITS_PER_TYPE(int)
+ * @ops: multiplexing operations for the parent IPI
+ * @data: opaque data used by the multiplexing operations
+ *
+ * If the parent IPI > 0 then ipi_mux_process() will be automatically
+ * called via chained handler.
+ *
+ * If the parent IPI <= 0 then it is responsibility of irqchip drivers
+ * to explicitly call ipi_mux_process() for processing muxed IPIs.
+ *
+ * Returns first virq of the newly created virtual IPIs upon success
+ * or <=0 upon failure
+ */
+int ipi_mux_create(unsigned int parent_virq, unsigned int nr_ipi,
+ const struct ipi_mux_ops *ops, void *data)
+{
+ struct fwnode_handle *fwnode;
+ struct irq_domain *domain;
+ int rc;
+
+ if (imux)
+ return -EEXIST;
+
+ if (BITS_PER_TYPE(int) < nr_ipi || !ops || !ops->ipi_mux_send)
+ return -EINVAL;
+
+ if (parent_virq &&
+ !irqd_is_per_cpu(irq_desc_get_irq_data(irq_to_desc(parent_virq))))
+ return -EINVAL;
+
+ imux = kzalloc(sizeof(*imux), GFP_KERNEL);
+ if (!imux)
+ return -ENOMEM;
+
+ imux->cpu = alloc_percpu(typeof(*imux->cpu));
+ if (!imux->cpu) {
+ rc = -ENOMEM;
+ goto fail_free_mux;
+ }
+
+ fwnode = irq_domain_alloc_named_fwnode("IPI-Mux");
+ if (!fwnode) {
+ pr_err("unable to create IPI Mux fwnode\n");
+ rc = -ENOMEM;
+ goto fail_free_cpu;
+ }
+
+ domain = irq_domain_create_simple(fwnode, nr_ipi, 0,
+ &ipi_mux_domain_ops, NULL);
+ if (!domain) {
+ pr_err("unable to add IPI Mux domain\n");
+ rc = -ENOMEM;
+ goto fail_free_fwnode;
+ }
+
+ domain->flags |= IRQ_DOMAIN_FLAG_IPI_SINGLE;
+ irq_domain_update_bus_token(domain, DOMAIN_BUS_IPI);
+
+ rc = __irq_domain_alloc_irqs(domain, -1, nr_ipi,
+ NUMA_NO_NODE, NULL, false, NULL);
+ if (rc <= 0) {
+ pr_err("unable to alloc IRQs from IPI Mux domain\n");
+ goto fail_free_domain;
+ }
+
+ imux->domain = domain;
+ imux->data = data;
+ imux->nr = nr_ipi;
+ imux->parent_virq = parent_virq;
+ imux->ops = ops;
+
+ if (imux->ops->ipi_mux_pre_handle)
+ static_branch_enable(&imux_pre_handle);
+
+ if (imux->ops->ipi_mux_post_handle)
+ static_branch_enable(&imux_post_handle);
+
+ if (parent_virq > 0)
+ irq_set_chained_handler(parent_virq, ipi_mux_handler);
+
+ return rc;
+
+fail_free_domain:
+ irq_domain_remove(domain);
+fail_free_fwnode:
+ irq_domain_free_fwnode(fwnode);
+fail_free_cpu:
+ free_percpu(imux->cpu);
+fail_free_mux:
+ kfree(imux);
+ imux = NULL;
+ return rc;
+}
--
2.34.1
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