Re: [PATCH v4 3/6] RISC-V: Treat IPIs as normal Linux IRQs

Marc Zyngier
2022-03-01T14:37:27Z

On Tue, 01 Mar 2022 04:27:19 +0000,
Anup Patel <apatel@ventanamicro.com> wrote:
>
> Currently, the RISC-V kernel provides arch specific hooks (i.e.
> struct riscv_ipi_ops) to register IPI handling methods. The stats
> gathering of IPIs is also arch specific in the RISC-V kernel.
>
> Other architectures (such as ARM, ARM64, and MIPS) have moved away
> from custom arch specific IPI handling methods. Currently, these
> architectures have Linux irqchip drivers providing a range of Linux
> IRQ numbers to be used as IPIs and IPI triggering is done using
> generic IPI APIs. This approach allows architectures to treat IPIs
> as normal Linux IRQs and IPI stats gathering is done by the generic
> Linux IRQ subsystem.
>
> We extend the RISC-V IPI handling as-per above approach so that arch
> specific IPI handling methods (struct riscv_ipi_ops) can be removed
> and the IPI handling is done through the Linux IRQ subsystem.
>
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> ---
> arch/riscv/Kconfig | 1 +
> arch/riscv/include/asm/ipi-mux.h | 43 ++++++
> arch/riscv/include/asm/sbi.h | 2 +
> arch/riscv/include/asm/smp.h | 35 +++--
> arch/riscv/kernel/Makefile | 1 +
> arch/riscv/kernel/cpu-hotplug.c | 3 +-
> arch/riscv/kernel/ipi-mux.c | 222 ++++++++++++++++++++++++++++++
> arch/riscv/kernel/irq.c | 3 +-
> arch/riscv/kernel/sbi.c | 13 +-
> arch/riscv/kernel/smp.c | 153 ++++++++++----------
> arch/riscv/kernel/smpboot.c | 5 +-
> drivers/clocksource/timer-clint.c | 8 +-
> drivers/irqchip/irq-riscv-intc.c | 55 ++++----
> 13 files changed, 405 insertions(+), 139 deletions(-)

This patch is huge and touches way too many things to be reviewed as
such. Please split arch-specific stuff from clocksource and irqchip,
going through a transition phase.

More below.

> create mode 100644 arch/riscv/include/asm/ipi-mux.h
> create mode 100644 arch/riscv/kernel/ipi-mux.c
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 5adcbd9b5e88..167681d6d3f8 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -54,6 +54,7 @@ config RISCV
> select GENERIC_GETTIMEOFDAY if HAVE_GENERIC_VDSO
> select GENERIC_IDLE_POLL_SETUP
> select GENERIC_IOREMAP if MMU
> + select GENERIC_IRQ_IPI
> select GENERIC_IRQ_MULTI_HANDLER
> select GENERIC_IRQ_SHOW
> select GENERIC_IRQ_SHOW_LEVEL
> diff --git a/arch/riscv/include/asm/ipi-mux.h b/arch/riscv/include/asm/ipi-mux.h
> new file mode 100644
> index 000000000000..988e2bba372a
> --- /dev/null
> +++ b/arch/riscv/include/asm/ipi-mux.h
> @@ -0,0 +1,43 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) 2022 Ventana Micro Systems Inc.
> + */
> +
> +#ifndef _ASM_RISCV_IPI_MUX_H
> +#define _ASM_RISCV_IPI_MUX_H
> +
> +struct cpumask;
> +
> +#ifdef CONFIG_SMP
> +
> +/* Handle muxed IPIs */
> +void riscv_ipi_mux_handle_irq(void);
> +
> +/* Create irq_domain for muxed IPIs */
> +struct irq_domain *riscv_ipi_mux_create(bool use_soft_irq,
> + void (*clear_ipi)(void),
> + void (*send_ipi)(const struct cpumask *mask));
> +
> +/* Destroy irq_domain for muxed IPIs */
> +void riscv_ipi_mux_destroy(struct irq_domain *d);
> +
> +#else
> +
> +static inline void riscv_ipi_mux_handle_irq(void)
> +{
> +}
> +
> +static inline struct irq_domain *riscv_ipi_mux_create(bool use_soft_irq,
> + void (*clear_ipi)(void),
> + void (*send_ipi)(const struct cpumask *mask))
> +{
> + return NULL;
> +}
> +
> +static inline void riscv_ipi_mux_destroy(struct irq_domain *d)
> +{
> +}
> +
> +#endif
> +
> +#endif /* _ASM_RISCV_IPI_MUX_H */
> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> index 06133b4f8e20..edd2c3135b4a 100644
> --- a/arch/riscv/include/asm/sbi.h
> +++ b/arch/riscv/include/asm/sbi.h
> @@ -133,6 +133,7 @@ struct sbiret {
> };
>
> void sbi_init(void);
> +void sbi_ipi_init(void);
> struct sbiret sbi_ecall(int ext, int fid, unsigned long arg0,
> unsigned long arg1, unsigned long arg2,
> unsigned long arg3, unsigned long arg4,
> @@ -202,6 +203,7 @@ static inline unsigned long sbi_mk_version(unsigned long major,
> int sbi_err_map_linux_errno(int err);
> #else /* CONFIG_RISCV_SBI */
> static inline int sbi_remote_fence_i(const struct cpumask *cpu_mask) { return -1; }
> +static inline void sbi_ipi_init(void) { }
> static inline void sbi_init(void) {}
> #endif /* CONFIG_RISCV_SBI */
> #endif /* _ASM_RISCV_SBI_H */
> diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
> index 23170c933d73..178fe4ada592 100644
> --- a/arch/riscv/include/asm/smp.h
> +++ b/arch/riscv/include/asm/smp.h
> @@ -15,11 +15,6 @@
> struct seq_file;
> extern unsigned long boot_cpu_hartid;
>
> -struct riscv_ipi_ops {
> - void (*ipi_inject)(const struct cpumask *target);
> - void (*ipi_clear)(void);
> -};
> -
> #ifdef CONFIG_SMP
> /*
> * Mapping between linux logical cpu index and hartid.
> @@ -33,9 +28,6 @@ void show_ipi_stats(struct seq_file *p, int prec);
> /* SMP initialization hook for setup_arch */
> void __init setup_smp(void);
>
> -/* Called from C code, this handles an IPI. */
> -void handle_IPI(struct pt_regs *regs);
> -
> /* Hook for the generic smp_call_function_many() routine. */
> void arch_send_call_function_ipi_mask(struct cpumask *mask);
>
> @@ -44,11 +36,17 @@ void arch_send_call_function_single_ipi(int cpu);
>
> int riscv_hartid_to_cpuid(int hartid);
>
> -/* Set custom IPI operations */
> -void riscv_set_ipi_ops(const struct riscv_ipi_ops *ops);
> +/* Enable IPI for CPU hotplug */
> +void riscv_ipi_enable(void);
> +
> +/* Disable IPI for CPU hotplug */
> +void riscv_ipi_disable(void);
>
> -/* Clear IPI for current CPU */
> -void riscv_clear_ipi(void);
> +/* Check if IPI interrupt numbers are available */
> +bool riscv_ipi_have_virq_range(void);
> +
> +/* Set the IPI interrupt numbers for arch (called by irqchip drivers) */
> +void riscv_ipi_set_virq_range(int virq, int nr_irqs);
>
> /* Secondary hart entry */
> asmlinkage void smp_callin(void);
> @@ -82,11 +80,20 @@ static inline unsigned long cpuid_to_hartid_map(int cpu)
> return boot_cpu_hartid;
> }
>
> -static inline void riscv_set_ipi_ops(const struct riscv_ipi_ops *ops)
> +static inline void riscv_ipi_enable(void)
> {
> }
>
> -static inline void riscv_clear_ipi(void)
> +static inline void riscv_ipi_disable(void)
> +{
> +}
> +
> +static inline bool riscv_ipi_have_virq_range(void)
> +{
> + return false;
> +}
> +
> +static inline void riscv_ipi_set_virq_range(int virq, int nr)
> {
> }
>
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index ffc87e76b1dd..5047723e5527 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -42,6 +42,7 @@ obj-$(CONFIG_RISCV_M_MODE) += traps_misaligned.o
> obj-$(CONFIG_FPU) += fpu.o
> obj-$(CONFIG_SMP) += smpboot.o
> obj-$(CONFIG_SMP) += smp.o
> +obj-$(CONFIG_SMP) += ipi-mux.o
> obj-$(CONFIG_SMP) += cpu_ops.o
>
> obj-$(CONFIG_RISCV_BOOT_SPINWAIT) += cpu_ops_spinwait.o
> diff --git a/arch/riscv/kernel/cpu-hotplug.c b/arch/riscv/kernel/cpu-hotplug.c
> index f7a832e3a1d1..39235cf50652 100644
> --- a/arch/riscv/kernel/cpu-hotplug.c
> +++ b/arch/riscv/kernel/cpu-hotplug.c
> @@ -13,7 +13,7 @@
> #include <asm/irq.h>
> #include <asm/cpu_ops.h>
> #include <asm/numa.h>
> -#include <asm/sbi.h>
> +#include <asm/smp.h>
>
> bool cpu_has_hotplug(unsigned int cpu)
> {
> @@ -43,6 +43,7 @@ int __cpu_disable(void)
> remove_cpu_topology(cpu);
> numa_remove_cpu(cpu);
> set_cpu_online(cpu, false);
> + riscv_ipi_disable();
> irq_migrate_all_off_this_cpu();
>
> return ret;
> diff --git a/arch/riscv/kernel/ipi-mux.c b/arch/riscv/kernel/ipi-mux.c
> new file mode 100644
> index 000000000000..3a0405f0e0de
> --- /dev/null
> +++ b/arch/riscv/kernel/ipi-mux.c
> @@ -0,0 +1,222 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Multiplex several IPIs over a single HW IPI.
> + *
> + * Copyright (c) 2022 Ventana Micro Systems Inc.
> + */
> +
> +#define pr_fmt(fmt) "riscv-ipi-mux: " fmt
> +#include <linux/cpu.h>
> +#include <linux/cpumask.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/smp.h>
> +#include <asm/ipi-mux.h>
> +
> +struct ipi_mux {
> + struct irq_domain *domain;
> + int parent_virq;
> + void (*clear_ipi)(void);
> + void (*send_ipi)(const struct cpumask *mask);
> +};

Why do you need this in the arch code? It really looks like something
that is irqchip specific (single IPI signal on which actual IPIs are
overlayed). It is also something that other irqchips are already
implementing, so there is potential for consolidation.

> +
> +static struct ipi_mux ipi_mux_priv;
> +static DEFINE_PER_CPU(unsigned long, ipi_mux_bits);
> +
> +static void ipi_mux_dummy(struct irq_data *d)
> +{
> +}
> +
> +static void ipi_mux_send_mask(struct irq_data *d, const struct cpumask *mask)
> +{
> + int cpu;
> +
> + /* Barrier before doing atomic bit update to IPI bits */
> + smp_mb__before_atomic();
> +
> + for_each_cpu(cpu, mask)
> + set_bit(d->hwirq, per_cpu_ptr(&ipi_mux_bits, cpu));
> +
> + /* Barrier after doing atomic bit update to IPI bits */
> + smp_mb__after_atomic();
> +
> + if (ipi_mux_priv.send_ipi)
> + ipi_mux_priv.send_ipi(mask);
> +}
> +
> +static struct irq_chip ipi_mux_chip = {
> + .name = "RISC-V IPI Mux",
> + .irq_mask = ipi_mux_dummy,
> + .irq_unmask = ipi_mux_dummy,
> + .ipi_send_mask = ipi_mux_send_mask,
> +};
> +
> +static int ipi_mux_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, &ipi_mux_chip, d->host_data,
> + handle_percpu_devid_irq, NULL, NULL);
> +
> + return 0;
> +}
> +
> +static int ipi_mux_domain_alloc(struct irq_domain *d, unsigned int virq,
> + unsigned int nr_irqs, void *arg)
> +{
> + int i, ret;
> + irq_hw_number_t hwirq;
> + unsigned int type = IRQ_TYPE_NONE;
> + struct irq_fwspec *fwspec = arg;
> +
> + ret = irq_domain_translate_onecell(d, fwspec, &hwirq, &type);
> + if (ret)
> + return ret;
> +
> + for (i = 0; i < nr_irqs; i++) {
> + ret = ipi_mux_domain_map(d, virq + i, hwirq + i);
> + if (ret)
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +static const struct irq_domain_ops ipi_mux_domain_ops = {
> + .translate = irq_domain_translate_onecell,
> + .alloc = ipi_mux_domain_alloc,
> + .free = irq_domain_free_irqs_top,
> +};
> +
> +void riscv_ipi_mux_handle_irq(void)
> +{
> + int err;
> + unsigned long irqs, *bits = this_cpu_ptr(&ipi_mux_bits);
> + irq_hw_number_t hwirq;
> +
> + while (true) {
> + if (ipi_mux_priv.clear_ipi)
> + ipi_mux_priv.clear_ipi();
> +
> + /* Order bit clearing and data access. */
> + mb();
> +
> + irqs = xchg(bits, 0);
> + if (!irqs)
> + break;
> +
> + for_each_set_bit(hwirq, &irqs, BITS_PER_LONG) {
> + err = generic_handle_domain_irq(ipi_mux_priv.domain,
> + hwirq);
> + if (unlikely(err))
> + pr_warn_ratelimited(
> + "can't find mapping for hwirq %lu\n",
> + hwirq);
> + }
> + }
> +}
> +
> +static void ipi_mux_handle_irq(struct irq_desc *desc)
> +{
> + struct irq_chip *chip = irq_desc_get_chip(desc);
> +
> + chained_irq_enter(chip, desc);
> + riscv_ipi_mux_handle_irq();
> + chained_irq_exit(chip, desc);
> +}
> +
> +static int ipi_mux_dying_cpu(unsigned int cpu)
> +{
> + if (ipi_mux_priv.parent_virq)
> + disable_percpu_irq(ipi_mux_priv.parent_virq);
> + return 0;
> +}
> +
> +static int ipi_mux_starting_cpu(unsigned int cpu)
> +{
> + if (ipi_mux_priv.parent_virq)
> + enable_percpu_irq(ipi_mux_priv.parent_virq,
> + irq_get_trigger_type(ipi_mux_priv.parent_virq));
> + return 0;
> +}
> +
> +struct irq_domain *riscv_ipi_mux_create(bool use_soft_irq,
> + void (*clear_ipi)(void),
> + void (*send_ipi)(const struct cpumask *mask))
> +{

There really shouldn't be a need for such a registration interface
anyway (the current idiom is to allocate IPIs in the root irqchip, and
pass them to the arch code).

Why can't you model it after the existing architectures?

> + int virq, parent_virq = 0;
> + struct irq_domain *domain;
> + struct irq_fwspec ipi;
> +
> + if (ipi_mux_priv.domain || riscv_ipi_have_virq_range())
> + return NULL;
> +
> + if (use_soft_irq) {
> + domain = irq_find_matching_fwnode(riscv_get_intc_hwnode(),
> + DOMAIN_BUS_ANY);
> + if (!domain) {
> + pr_err("unable to find INTC IRQ domain\n");
> + return NULL;
> + }
> +
> + parent_virq = irq_create_mapping(domain, RV_IRQ_SOFT);
> + if (!parent_virq) {
> + pr_err("unable to create INTC IRQ mapping\n");
> + return NULL;
> + }
> + }
> +
> + domain = irq_domain_add_linear(NULL, BITS_PER_LONG,
> + &ipi_mux_domain_ops, NULL);
> + if (!domain) {
> + pr_err("unable to add IPI Mux domain\n");
> + goto fail_dispose_mapping;
> + }
> +
> + ipi.fwnode = domain->fwnode;
> + ipi.param_count = 1;
> + ipi.param[0] = 0;
> + virq = __irq_domain_alloc_irqs(domain, -1, BITS_PER_LONG,
> + NUMA_NO_NODE, &ipi, false, NULL);
> + if (virq <= 0) {
> + pr_err("unable to alloc IRQs from IPI Mux domain\n");
> + goto fail_domain_remove;
> + }
> +
> + ipi_mux_priv.domain = domain;
> + ipi_mux_priv.parent_virq = parent_virq;
> + ipi_mux_priv.clear_ipi = clear_ipi;
> + ipi_mux_priv.send_ipi = send_ipi;
> +
> + if (parent_virq)
> + irq_set_chained_handler(parent_virq, ipi_mux_handle_irq);
> +
> + cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
> + "irqchip/riscv/ipi-mux:starting",
> + ipi_mux_starting_cpu, ipi_mux_dying_cpu);
> +
> + riscv_ipi_set_virq_range(virq, BITS_PER_LONG);
> +
> + return ipi_mux_priv.domain;
> +
> +fail_domain_remove:
> + irq_domain_remove(domain);
> +fail_dispose_mapping:
> + if (parent_virq)
> + irq_dispose_mapping(parent_virq);
> + return NULL;
> +}
> +
> +void riscv_ipi_mux_destroy(struct irq_domain *d)
> +{
> + if (!d || ipi_mux_priv.domain != d)
> + return;
> +
> + irq_domain_remove(ipi_mux_priv.domain);
> + if (ipi_mux_priv.parent_virq)
> + irq_dispose_mapping(ipi_mux_priv.parent_virq);
> + memset(&ipi_mux_priv, 0, sizeof(ipi_mux_priv));
> +}

Err... Under which circumstances do you destroy such an irqdomain?
Once all the CPUs have been removed from the machine?

I really think you should aim for a simpler abstraction. The arch code
should deal with the interrupts themselves, and leave the
*implementation* of the IPI to the driver code, potentially shared
across irqchips. This would avoid creating more new interfaces that
are specific to one architecture or another.

M.

--
Without deviation from the norm, progress is not possible.