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 <redacted>
---
 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@kernel.org>

Will

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