Messages in this thread | | | From | Rob Herring <> | Date | Thu, 21 Jan 2021 10:40:17 -0600 | Subject | Re: [RFC PATCH 7/7] irqchip/apple-aic: add SMP support to the Apple AIC driver. |
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On Thu, Jan 21, 2021 at 6:52 AM Mohamed Mediouni <mohamed.mediouni@caramail.com> wrote: > > > > > On 21 Jan 2021, at 13:44, Arnd Bergmann <arnd@kernel.org> wrote: > > > > On Wed, Jan 20, 2021 at 2:27 PM Mohamed Mediouni > > <mohamed.mediouni@caramail.com> wrote: > > > >> +#ifdef CONFIG_SMP > >> +static void apple_aic_ipi_send_mask(struct irq_data *d, > >> + const struct cpumask *mask) > > > > Not sure we care about the #ifdef here, given that arch/arm64 does not > > allow building a kernel without CONFIG_SMP. > > > >> + /* > >> + * Ensure that stores to Normal memory are visible to the > >> + * other CPUs before issuing the IPI. > >> + */ > >> + wmb(); > >> + > >> + for_each_cpu (cpu, mask) { > >> + smp_mb__before_atomic(); > >> + atomic_or(1u << irqnr, per_cpu_ptr(&aic_ipi_mask, cpu)); > >> + smp_mb__after_atomic(); > >> + lcpu = get_cpu(); > >> + if (aic.fast_ipi) { > >> + if ((lcpu >> 2) == (cpu >> 2)) > >> + write_sysreg(cpu & 3, SR_APPLE_IPI_LOCAL); > >> + else > >> + write_sysreg((cpu & 3) | ((cpu >> 2) << 16), > >> + SR_APPLE_IPI_REMOTE); > >> + } else > >> + writel(lcpu == cpu ? REG_IPI_FLAG_SELF : > >> + (REG_IPI_FLAG_OTHER << cpu), > >> + aic.base + REG_IPI_SET); > >> + put_cpu(); > >> + } > >> + > >> + /* Force the above writes to be executed */ > >> + if (aic.fast_ipi) > >> + isb(); > >> +} > > > > Since this just loops over all CPUs, I'd probably just turn it into > > an ipi_send_single() callback and have the caller do the > > loop for simplicity. > > > > I also have the feeling that splitting one hardware IPI into multiple > > logical interrupts, which are then all registered by the same irq > > handler adds a little more complexity than necessary. > > > > Changing this would of course require modifications to > > arch/arm64/kernel/smp.c, which is hardwired to use > > CONFIG_GENERIC_IRQ_IPI in smp_cross_call(), and allowing > > a different code path there may be worse than emulating an > > irqchip. > > > >> @@ -186,8 +325,11 @@ static int __init apple_aic_init(struct device_node *node, > >> if (WARN(!aic.base, "unable to map aic registers\n")) > >> return -EINVAL; > >> > >> + aic.fast_ipi = of_property_read_bool(node, "fast-ipi"); > > > > Where is this property documented, and what decides which one to use? > It’s getting documented in the next patch set. > > This property is there to enable support for older iPhone processors > later on, some of which do not have fast IPI support. > > On Apple M1, fast-ipi is always on.
This should be implied by the compatible string which needs to be more specific and include the SoC name.
Rob
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