linux-kernel - Re: [PATCH v4 15/18] irqchip/apple-aic: Add support for the Apple Interrupt Controller

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Message-ID: <20210407210940.GC16198@willie-the-truck>
Date:   Wed, 7 Apr 2021 22:09:41 +0100
From:   Will Deacon <will@...nel.org>
To:     Hector Martin <marcan@...can.st>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <maz@...nel.org>, Rob Herring <robh@...nel.org>,
        Arnd Bergmann <arnd@...nel.org>,
        Olof Johansson <olof@...om.net>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Tony Lindgren <tony@...mide.com>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Stan Skowronek <stan@...ellium.com>,
        Alexander Graf <graf@...zon.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Hellwig <hch@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 15/18] irqchip/apple-aic: Add support for the Apple
 Interrupt Controller

On Fri, Apr 02, 2021 at 06:05:39PM +0900, Hector Martin wrote:
> This is the root interrupt controller used on Apple ARM SoCs such as the
> M1. This irqchip driver performs multiple functions:
> 
> * Handles both IRQs and FIQs
> 
> * Drives the AIC peripheral itself (which handles IRQs)
> 
> * Dispatches FIQs to downstream hard-wired clients (currently the ARM
>   timer).
> 
> * Implements a virtual IPI multiplexer to funnel multiple Linux IPIs
>   into a single hardware IPI
> 
> Signed-off-by: Hector Martin <marcan@...can.st>
> ---
>  MAINTAINERS                     |   2 +
>  drivers/irqchip/Kconfig         |   8 +
>  drivers/irqchip/Makefile        |   1 +
>  drivers/irqchip/irq-apple-aic.c | 837 ++++++++++++++++++++++++++++++++
>  include/linux/cpuhotplug.h      |   1 +
>  5 files changed, 849 insertions(+)
>  create mode 100644 drivers/irqchip/irq-apple-aic.c

Couple of stale comment nits:

> +static void aic_ipi_unmask(struct irq_data *d)
> +{
> +	struct aic_irq_chip *ic = irq_data_get_irq_chip_data(d);
> +	u32 irq_bit = BIT(irqd_to_hwirq(d));
> +
> +	atomic_or(irq_bit, this_cpu_ptr(&aic_vipi_enable));
> +
> +	/*
> +	 * The atomic_or() above must complete before the atomic_read_acquire() below to avoid
> +	 * racing aic_ipi_send_mask().
> +	 */

(the atomic_read_acquire() is now an atomic_read())

> +	smp_mb__after_atomic();
> +
> +	/*
> +	 * If a pending vIPI was unmasked, raise a HW IPI to ourselves.
> +	 * No barriers needed here since this is a self-IPI.
> +	 */
> +	if (atomic_read(this_cpu_ptr(&aic_vipi_flag)) & irq_bit)
> +		aic_ic_write(ic, AIC_IPI_SEND, AIC_IPI_SEND_CPU(smp_processor_id()));
> +}
> +
> +static void aic_ipi_send_mask(struct irq_data *d, const struct cpumask *mask)
> +{
> +	struct aic_irq_chip *ic = irq_data_get_irq_chip_data(d);
> +	u32 irq_bit = BIT(irqd_to_hwirq(d));
> +	u32 send = 0;
> +	int cpu;
> +	unsigned long pending;
> +
> +	for_each_cpu(cpu, mask) {
> +		/*
> +		 * This sequence is the mirror of the one in aic_ipi_unmask();
> +		 * see the comment there. Additionally, release semantics
> +		 * ensure that the vIPI flag set is ordered after any shared
> +		 * memory accesses that precede it. This therefore also pairs
> +		 * with the atomic_fetch_andnot in aic_handle_ipi().
> +		 */
> +		pending = atomic_fetch_or_release(irq_bit, per_cpu_ptr(&aic_vipi_flag, cpu));
> +
> +		/*
> +		 * The atomic_fetch_or_release() above must complete before the
> +		 * atomic_read_acquire() below to avoid racing aic_ipi_unmask().
> +		 */

(same here)

> +		smp_mb__after_atomic();
> +
> +		if (!(pending & irq_bit) &&
> +		    (atomic_read(per_cpu_ptr(&aic_vipi_enable, cpu)) & irq_bit))
> +			send |= AIC_IPI_SEND_CPU(cpu);
> +	}

But with that:

Acked-by: Will Deacon <will@...nel.org>

Will