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

[Marc Zyngier <maz@kernel.org>]

On Thu, 04 Feb 2021 20:39:48 +0000,
Hector Martin <marcan@marcan.st> wrote:
> 
> This is the root interrupt controller used on Apple ARM SoCs such as the
> M1. This irqchip driver performs multiple functions:
> 
> * Discriminates between IRQs and FIQs
> 
> * Drives the AIC peripheral itself (which handles IRQs)
> 
> * Dispatches FIQs to downstream hard-wired clients (currently the ARM
>   timer).
> 
> This patch introduces basic UP irqchip support, without SMP/IPI support.
> 
> Signed-off-by: Hector Martin <marcan@marcan.st>
> ---
>  MAINTAINERS                     |   1 +
>  drivers/irqchip/Kconfig         |  10 +
>  drivers/irqchip/Makefile        |   1 +
>  drivers/irqchip/irq-apple-aic.c | 316 ++++++++++++++++++++++++++++++++
>  4 files changed, 328 insertions(+)
>  create mode 100644 drivers/irqchip/irq-apple-aic.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f3d4661731c8..3a54ee5747d3 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -1635,6 +1635,7 @@ C:	irc://chat.freenode.net/asahi-dev
>  T:	git https://github.com/AsahiLinux/linux.git
>  F:	Documentation/devicetree/bindings/arm/AAPL.yaml
>  F:	Documentation/devicetree/bindings/interrupt-controller/AAPL,aic.yaml
> +F:	drivers/irqchip/irq-apple-aic.c
>  F:	include/dt-bindings/interrupt-controller/apple-aic.h
>  
>  ARM/ARTPEC MACHINE SUPPORT
> diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
> index b147f22a78f4..288c01a9abd4 100644
> --- a/drivers/irqchip/Kconfig
> +++ b/drivers/irqchip/Kconfig
> @@ -590,4 +590,14 @@ config MST_IRQ
>  	help
>  	  Support MStar Interrupt Controller.
>  
> +config APPLE_AIC
> +	bool "Apple Interrupt Controller (AIC)"
> +	depends on ARCH_APPLE || COMPILE_TEST
> +	default ARCH_APPLE
> +	select IRQ_DOMAIN
> +	select IRQ_DOMAIN_HIERARCHY
> +	help
> +	  Support for the Apple Interrupt Controller found on Apple Silicon SoCs,
> +	  such as the M1.
> +
>  endmenu
> diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
> index 0ac93bfaec61..0e2ba7c2dce7 100644
> --- a/drivers/irqchip/Makefile
> +++ b/drivers/irqchip/Makefile
> @@ -113,3 +113,4 @@ obj-$(CONFIG_LOONGSON_PCH_PIC)		+= irq-loongson-pch-pic.o
>  obj-$(CONFIG_LOONGSON_PCH_MSI)		+= irq-loongson-pch-msi.o
>  obj-$(CONFIG_MST_IRQ)			+= irq-mst-intc.o
>  obj-$(CONFIG_SL28CPLD_INTC)		+= irq-sl28cpld.o
> +obj-$(CONFIG_APPLE_AIC)			+= irq-apple-aic.o
> diff --git a/drivers/irqchip/irq-apple-aic.c b/drivers/irqchip/irq-apple-aic.c
> new file mode 100644
> index 000000000000..533e3ce9f432
> --- /dev/null
> +++ b/drivers/irqchip/irq-apple-aic.c
> @@ -0,0 +1,316 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright 2021 Hector Martin <marcan@marcan.st>
> + *
> + * Based on irq-lpc32xx:
> + *   Copyright 2015-2016 Vladimir Zapolskiy <vz@mleia.com>
> + * Based on irq-bcm2836:
> + *   Copyright 2015 Broadcom
> + */
> +
> +/*
> + * AIC is a fairly simple interrupt controller with the following features:
> + *
> + * - 896 level-triggered hardware IRQs
> + *   - Single mask bit per IRQ
> + *   - Per-IRQ affinity setting
> + *   - Automatic masking on event delivery (auto-ack)
> + *   - Software triggering (ORed with hw line)
> + * - 2 per-CPU IPIs (meant as "self" and "other", but they are interchangeable if not symmetric)
> + * - Automatic prioritization (single event/ack register per CPU, lower IRQs = higher priority)
> + * - Automatic masking on ack
> + * - Default "this CPU" register view and explicit per-CPU views
> + *
> + * In addition, this driver also handles FIQs, as these are routed to the same IRQ vector. These
> + * are used for Fast IPIs (TODO) and the ARMv8 timer IRQs.
> + *
> + * Implementation notes:
> + *
> + * - This driver creates one IRQ domain for HW IRQs and the timer FIQs
> + * - FIQ hwirq numbers are assigned after true hwirqs, and are per-cpu
> + * - DT bindings use 3-cell form (like GIC):
> + *   - <0 nr flags> - hwirq #nr
> + *   - <1 nr flags> - FIQ #nr
> + *     - nr=0  physical timer
> + *     - nr=1  virtual timer
> + *   - <2 nr flags> - IPI #nr
> + *     - nr=0  other IPI
> + *     - nr=1  self IPI

I really do not want to expose IPIs in the DT. The OS defines what
IPIs are used for, not the firmware/HW. No other platform requires
this either, so is there any reason to do so?

> + *
> + */
> +
> +#define pr_fmt(fmt) "%s: " fmt, __func__
> +
> +#include <linux/io.h>
> +#include <linux/irqchip.h>
> +#include <linux/irqchip/chained_irq.h>

There isn't any chained interrupt controller here, AFAICT.

> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +#include <linux/of_platform.h>
> +#include <linux/slab.h>
> +#include <asm/exception.h>
> +
> +#include <dt-bindings/interrupt-controller/apple-aic.h>
> +
> +#define AIC_INFO		0x0004
> +#define AIC_INFO_NR_HW(i)	((i) & 0x0000ffff)
> +
> +#define AIC_CONFIG		0x0010
> +
> +#define AIC_WHOAMI		0x2000
> +#define AIC_EVENT		0x2004
> +
> +#define AIC_EVENT_TYPE_HW	1
> +#define AIC_EVENT_TYPE_IPI	4
> +#define AIC_EVENT_IPI_OTHER	1
> +#define AIC_EVENT_IPI_SELF	2
> +
> +#define AIC_IPI_SEND		0x2008
> +#define AIC_IPI_ACK		0x200c
> +#define AIC_IPI_MASK_SET	0x2024
> +#define AIC_IPI_MASK_CLR	0x2028
> +
> +#define AIC_IPI_SEND_CPU(cpu)	BIT(cpu)
> +
> +#define AIC_IPI_OTHER		BIT(0)
> +#define AIC_IPI_SELF		BIT(31)
> +
> +#define AIC_TARGET_CPU		0x3000
> +#define AIC_SW_SET		0x4000
> +#define AIC_SW_CLR		0x4080
> +#define AIC_MASK_SET		0x4100
> +#define AIC_MASK_CLR		0x4180
> +
> +#define AIC_CPU_IPI_SET(cpu)	(0x5008 + (cpu << 7))
> +#define AIC_CPU_IPI_CLR(cpu)	(0x500c + (cpu << 7))
> +#define AIC_CPU_IPI_MASK_SET(cpu) (0x5024 + (cpu << 7))
> +#define AIC_CPU_IPI_MASK_CLR(cpu) (0x5028 + (cpu << 7))
> +
> +#define MASK_REG(x)		(4 * ((x) >> 5))
> +#define MASK_BIT(x)		BIT((x) & 0x1f)
> +
> +#define AIC_NR_FIQ		2
> +#define AIC_NR_IPI		2
> +
> +/*
> + * Max 31 bits in IPI SEND register (top bit is self).
> + * >=32-core chips will need code changes anyway.
> + */
> +#define AIC_MAX_CPUS 31
> +
> +struct aic_irq_chip {
> +	void __iomem *base;
> +	struct irq_domain *hw_domain;
> +	int nr_hw;
> +};
> +
> +static struct aic_irq_chip *aic_irqc;
> +
> +static inline u32 aic_ic_read(struct aic_irq_chip *ic, u32 reg)

Please drop the inline, the compiler should manage this on its own
(and in most case will totally ignore that keyword one way or
another).

> +{
> +	return readl(ic->base + reg);

Please consider using the _relaxed accessors, as I don't think any of
these interacts with memory (apart from IPIs, of course).

> +}
> +
> +static inline void aic_ic_write(struct aic_irq_chip *ic, u32 reg, u32 val)
> +{
> +	writel(val, ic->base + reg);
> +}
> +
> +/* These functions do nothing for FIQs, because they have no masks */
> +static void aic_irq_mask(struct irq_data *d)
> +{
> +	struct aic_irq_chip *ic = irq_data_get_irq_chip_data(d);
> +
> +	if (d->hwirq < ic->nr_hw)
> +		aic_ic_write(ic, AIC_MASK_SET + MASK_REG(d->hwirq),
> +			     MASK_BIT(d->hwirq));
> +}

If these functions have no impact on the per-CPU interrupts, then
maybe these interrupts should be given a different irqchip.

> +
> +static void aic_irq_unmask(struct irq_data *d)
> +{
> +	struct aic_irq_chip *ic = irq_data_get_irq_chip_data(d);
> +
> +	if (d->hwirq < ic->nr_hw)
> +		aic_ic_write(ic, AIC_MASK_CLR + MASK_REG(d->hwirq),
> +			     MASK_BIT(d->hwirq));
> +}
> +
> +static void aic_irq_eoi(struct irq_data *d)
> +{
> +	/*
> +	 * Reading the interrupt reason automatically acknowledges and masks
> +	 * the IRQ, so we just unmask it here if needed.
> +	 */
> +	if (!irqd_irq_disabled(d) && !irqd_irq_masked(d))
> +		aic_irq_unmask(d);

This doesn't apply to per-CPU interrupts, right? Or does it?

> +}
> +
> +static void aic_handle_irq(struct pt_regs *regs)
> +{
> +	struct aic_irq_chip *ic = aic_irqc;
> +	u32 event = aic_ic_read(ic, AIC_EVENT);
> +
> +	while (event) {
> +		u32 type = event >> 16, irq = event & 0xffff;

Nit: please consider introducing masks and using the bitfield macros
to extract the various fields.

> +
> +		/* AIC_EVENT is read-sensitive, ensure it happens before we proceed */
> +		isb();

You seem to have a data dependency after this, so I can't see how the
ISB influences the read from AIC_EVENT. However you need to order it
with the read from the timer registers, and I believe it'd be better
to move the barrier there.

> +
> +		if (type == AIC_EVENT_TYPE_HW) {
> +			handle_domain_irq(aic_irqc->hw_domain, irq, regs);
> +		} else if (type == AIC_EVENT_TYPE_IPI) {
> +			handle_domain_irq(aic_irqc->hw_domain,
> +					  ic->nr_hw + AIC_NR_FIQ + irq - 1, regs);

nit: it would be slightly less cumbersome to compute the hwirq in a
switch, and have a single call to handle_domain_irq().

I also wonder whether using two top-level domains would be better. Not
a big deal though.

> +		} else {
> +			pr_err("spurious IRQ event %d, %d\n", type, irq);

Spurious interrupts aren't an error, in general. If you really want to
keep this, at the very least make it rate-limited.

> +		}
> +
> +		event = aic_ic_read(ic, AIC_EVENT);

Consider turning the whole thing into a do{}while() so that there is
only a single read of AIC_EVENT in the function.

> +	}
> +}
> +
> +#define TIMER_FIRING(x)                                                        \
> +	(((x) & (ARCH_TIMER_CTRL_ENABLE | ARCH_TIMER_CTRL_IT_MASK |            \
> +		 ARCH_TIMER_CTRL_IT_STAT)) ==                                  \
> +	 (ARCH_TIMER_CTRL_ENABLE | ARCH_TIMER_CTRL_IT_STAT))
> +
> +static void aic_handle_fiq(struct pt_regs *regs)
> +{
> +	/*
> +	 * It would be really nice to find a system register that lets us get the FIQ source
> +	 * state without having to peek down into clients...
> +	 */

nit: please try to keep comments within the 80 cols limit. I don't
mind code being wider, but comments benefit from being more rigorously
structured.

And yes, having to poll each end-point IP is really a drag. How does
the PMU work on this system? Is there any other per-CPU source?

> +	if (TIMER_FIRING(read_sysreg(cntp_ctl_el0))) {
> +		handle_domain_irq(aic_irqc->hw_domain,
> +				  aic_irqc->nr_hw + AIC_TMR_PHYS, regs);
> +	}
> +
> +	if (TIMER_FIRING(read_sysreg(cntv_ctl_el0))) {
> +		handle_domain_irq(aic_irqc->hw_domain,
> +				  aic_irqc->nr_hw + AIC_TMR_VIRT, regs);
> +	}

This system runs VHE, so there is also CNT{P,V}_CTL_EL02 to consider.
But I really wonder how the whole thing works once these two timers
are assigned to a guest. Somehow, something must control the masking,
otherwise you wouldn't be able to enter a guest with a timer firing.

It also means that there is no way to have threaded per-CPU
interrupts, which means no Preempt-RT. You could wire the mask/unmask
callbacks to mess with the IMASK bit in individual timers, but that
doesn't solve the problem for guests.

> +}
> +
> +static void __exception_irq_entry aic_handle_irq_or_fiq(struct pt_regs *regs)
> +{
> +	u64 isr = read_sysreg(isr_el1);
> +
> +	if (isr & PSR_F_BIT)
> +		aic_handle_fiq(regs);
> +
> +	if (isr & PSR_I_BIT)
> +		aic_handle_irq(regs);
> +}
> +
> +static struct irq_chip aic_chip = {
> +	.name = "AIC",
> +	.irq_mask = aic_irq_mask,
> +	.irq_unmask = aic_irq_unmask,
> +	.irq_eoi = aic_irq_eoi,
> +};
> +
> +static int aic_irq_domain_map(struct irq_domain *id, unsigned int irq,
> +			      irq_hw_number_t hw)
> +{
> +	struct aic_irq_chip *ic = id->host_data;
> +
> +	irq_set_chip_data(irq, ic);
> +	if (hw < ic->nr_hw) {
> +		irq_set_chip_and_handler(irq, &aic_chip, handle_fasteoi_irq);
> +	} else {
> +		irq_set_percpu_devid(irq);
> +		irq_set_chip_and_handler(irq, &aic_chip,
> +					 handle_percpu_devid_irq);
> +	}
> +	irq_set_status_flags(irq, IRQ_LEVEL);

Are all interrupts level? How are MSIs implemented?

> +	irq_set_noprobe(irq);
> +
> +	return 0;
> +}
> +
> +static void aic_irq_domain_unmap(struct irq_domain *id, unsigned int irq)
> +{
> +	irq_set_chip_and_handler(irq, NULL, NULL);
> +}
> +
> +static int aic_irq_domain_xlate(struct irq_domain *id,
> +				struct device_node *ctrlr, const u32 *intspec,
> +				unsigned int intsize,
> +				irq_hw_number_t *out_hwirq,
> +				unsigned int *out_type)
> +{
> +	struct aic_irq_chip *ic = id->host_data;
> +
> +	if (intsize != 3)
> +		return -EINVAL;
> +
> +	if (intspec[0] == AIC_IRQ && intspec[1] < ic->nr_hw)
> +		*out_hwirq = intspec[1];
> +	else if (intspec[0] == AIC_FIQ && intspec[1] < AIC_NR_FIQ)
> +		*out_hwirq = ic->nr_hw + intspec[1];
> +	else if (intspec[0] == AIC_IPI && intspec[1] < AIC_NR_IPI)
> +		*out_hwirq = ic->nr_hw + AIC_NR_FIQ + intspec[1];
> +	else
> +		return -EINVAL;
> +
> +	*out_type = intspec[2] & IRQ_TYPE_SENSE_MASK;
> +
> +	return 0;
> +}
> +
> +static const struct irq_domain_ops aic_irq_domain_ops = {
> +	.map = aic_irq_domain_map,
> +	.unmap = aic_irq_domain_unmap,
> +	.xlate = aic_irq_domain_xlate,
> +};
> +
> +static int __init aic_of_ic_init(struct device_node *node,
> +				 struct device_node *parent)
> +{
> +	int i;
> +	void __iomem *regs;
> +	u32 info;
> +	struct aic_irq_chip *irqc;
> +
> +	regs = of_iomap(node, 0);
> +	if (WARN_ON(!regs))
> +		return -EIO;
> +
> +	irqc = kzalloc(sizeof(*irqc), GFP_KERNEL);
> +	if (!irqc)
> +		return -ENOMEM;
> +
> +	aic_irqc = irqc;
> +	irqc->base = regs;
> +
> +	info = aic_ic_read(irqc, AIC_INFO);
> +	irqc->nr_hw = AIC_INFO_NR_HW(info);
> +
> +	irqc->hw_domain =
> +		irq_domain_add_linear(node,
> +				      irqc->nr_hw + AIC_NR_FIQ + AIC_NR_IPI,
> +				      &aic_irq_domain_ops, irqc);

Please keep assignments on a single line.

> +	if (WARN_ON(!irqc->hw_domain)) {
> +		iounmap(irqc->base);
> +		kfree(irqc);
> +		return -ENODEV;
> +	}
> +
> +	irq_domain_update_bus_token(irqc->hw_domain, DOMAIN_BUS_WIRED);
> +
> +	set_handle_irq(aic_handle_irq_or_fiq);
> +
> +	for (i = 0; i < BITS_TO_LONGS(irqc->nr_hw); i++)

long is 64bit on arm64, so this loop is unlikely to do what you
want. Consider using BITS_TO_U32.

> +		aic_ic_write(irqc, AIC_MASK_SET + i * 4, ~0);
> +	for (i = 0; i < BITS_TO_LONGS(irqc->nr_hw); i++)
> +		aic_ic_write(irqc, AIC_SW_CLR + i * 4, ~0);
> +	for (i = 0; i < irqc->nr_hw; i++)
> +		aic_ic_write(irqc, AIC_TARGET_CPU + i * 4, 1);
> +
> +	pr_info("AIC: initialized with %d IRQs, %d FIQs, %d IPIs\n",
> +		irqc->nr_hw, AIC_NR_FIQ, AIC_NR_IPI);
> +
> +	return 0;
> +}
> +
> +IRQCHIP_DECLARE(apple_m1_aic, "AAPL,aic", aic_of_ic_init);

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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