Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH v14 3/8] genirq: Add mechanism to multiplex a single HW IPI | Date | Thu, 01 Dec 2022 18:20:25 +0100 |
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On Thu, Dec 01 2022 at 18:31, Anup Patel 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
s/we//
> mechanism which help us create multiple virtual IPIs using a single > HW IPI. This generic IPI multiplexing is inspired from the Apple AIC
s/from/by/
> irqchip driver and it is shared by various RISC-V irqchip drivers.
Sure, but now we have two copies of this. One in the Apple AIC and one here. The obvious thing to do is:
1) Provide generic infrastructure
2) Convert AIC to use it
3) Add RISCV users
No?
> +static void ipi_mux_mask(struct irq_data *d) > +{ > + struct ipi_mux_cpu *icpu = this_cpu_ptr(ipi_mux_pcpu); > + > + 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(ipi_mux_pcpu);
The AIC code got the variable ordering correct ...
https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#variable-declarations
> + 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) > + ipi_mux_send(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(ipi_mux_pcpu); > + unsigned long pending; > + int cpu; > + > + for_each_cpu(cpu, mask) { > + icpu = per_cpu_ptr(ipi_mux_pcpu, cpu); > + pending = atomic_fetch_or_release(ibit, &icpu->bits); > + > + /* > + * The atomic_fetch_or_release() above must complete > + * before the atomic_read() below to avoid racing with > + * ipi_mux_unmask(). > + */ > + smp_mb__after_atomic(); > + > + /* > + * The flag writes must complete before the physical IPI is > + * issued to another CPU. This is implied by the control > + * dependency on the result of atomic_read() below, which is > + * itself already ordered after the vIPI flag write. > + */ > + if (!(pending & ibit) && (atomic_read(&icpu->enable) & ibit)) > + ipi_mux_send(cpu); > + } > +} > + > +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, NULL, > + 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(ipi_mux_pcpu); > + irq_hw_number_t hwirq; > + unsigned long ipis; > + unsigned int en; > + > + /* > + * 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().
The comments in the AIC code where you copied from are definitely better...
Thanks,
tglx
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