Messages in this thread | | | Date | Thu, 21 Jul 2022 12:00:23 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH v7 3/7] genirq: Add mechanism to multiplex a single HW IPI |
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On Wed, 20 Jul 2022 16:23:44 +0100, Anup Patel <apatel@ventanamicro.com> wrote: > > 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 shared among various RISC-V > irqchip drivers. > > Signed-off-by: Anup Patel <apatel@ventanamicro.com> > --- > include/linux/irq.h | 16 ++++ > kernel/irq/Kconfig | 4 + > kernel/irq/Makefile | 1 + > kernel/irq/ipi-mux.c | 199 +++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 220 insertions(+) > create mode 100644 kernel/irq/ipi-mux.c > > diff --git a/include/linux/irq.h b/include/linux/irq.h > index 505308253d23..a97bf13a8965 100644 > --- a/include/linux/irq.h > +++ b/include/linux/irq.h > @@ -1249,6 +1249,22 @@ 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_clear: Optional function to clear parent IPI > + * @ipi_mux_send: Trigger parent IPI on target CPUs > + */ > +struct ipi_mux_ops { > + void (*ipi_mux_clear)(unsigned int parent_virq); > + void (*ipi_mux_send)(unsigned int parent_virq, > + 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); > + > #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 10929eda9825..2388e7d40ed3 100644 > --- a/kernel/irq/Kconfig > +++ b/kernel/irq/Kconfig > @@ -84,6 +84,10 @@ config GENERIC_IRQ_IPI > bool > select IRQ_DOMAIN_HIERARCHY > > +# Generic IRQ IPI Mux support > +config GENERIC_IRQ_IPI_MUX > + bool > + > # 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..bd6b31ca588b > --- /dev/null > +++ b/kernel/irq/ipi-mux.c > @@ -0,0 +1,199 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * Multiplex several virtual IPIs over a single HW IPI. > + * > + * 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/smp.h> > + > +static unsigned int ipi_mux_nr; > +static unsigned int ipi_mux_parent_virq; > +static struct irq_domain *ipi_mux_domain; > +static const struct ipi_mux_ops *ipi_mux_ops; > +static DEFINE_PER_CPU(unsigned long, ipi_mux_bits); > + > +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(); > + > + /* Trigger the parent IPI */ > + ipi_mux_ops->ipi_mux_send(ipi_mux_parent_virq, mask); > +} > + > +static const struct irq_chip ipi_mux_chip = { > + .name = "IPI Mux", > + .ipi_send_mask = ipi_mux_send_mask,
I've given this a bit more though, and I came to the conclusion that we really should have the full masking semantics here, even if Linux currently doesn't really use it.
It makes the handling a bit more complex, and unmasking a pending IPI must be handled gracefully, but we already have implemented most of that code in the irq-apple-aic driver.
And if we go down this road, such a driver should be very easy to move over this infrastructure, making the change a lot more palatable.
M.
-- Without deviation from the norm, progress is not possible.
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