Message-ID: <86d0rq35o1.wl-marc.zyngier@arm.com>
Date:   Wed, 31 Oct 2018 08:02:22 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Phil Edworthy <phil.edworthy@...esas.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        <linux-renesas-soc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] irqchip: Add support for Renesas RZ/N1 GPIO interrupt multiplexer

Hi Phil,

On Tue, 30 Oct 2018 10:44:38 +0000,
Phil Edworthy <phil.edworthy@...esas.com> wrote:
> 
> On RZ/N1 devices, there are 3 Synopsys DesignWare GPIO blocks each
> configured to have 32 interrupt outputs, so we have a total of 96 GPIO
> interrupts. All of these are passed to the GPIO IRQ Muxer, which selects
> 8 of the GPIO interrupts to pass onto the GIC. The interrupt signals
> aren't latched, so there is nothing to do in this driver when an interrupt
> is received, other than tell the corresponding GPIO block.
> 
> Signed-off-by: Phil Edworthy <phil.edworthy@...esas.com>
> ---
> v2:
>  - Use interrupt-map to allow the GPIO controller info to be specified
>    as part of the irq.
>  - Renamed struct and funcs from 'girq' to a more comprehenisble 'irqmux'.
> ---
>  drivers/irqchip/Kconfig        |  10 ++
>  drivers/irqchip/Makefile       |   1 +
>  drivers/irqchip/rzn1-irq-mux.c | 235 +++++++++++++++++++++++++++++++++
>  3 files changed, 246 insertions(+)
>  create mode 100644 drivers/irqchip/rzn1-irq-mux.c
> 
> diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
> index 96451b581452..3a60a8af60dd 100644
> --- a/drivers/irqchip/Kconfig
> +++ b/drivers/irqchip/Kconfig
> @@ -204,6 +204,16 @@ config RENESAS_IRQC
>  	select GENERIC_IRQ_CHIP
>  	select IRQ_DOMAIN
>  
> +config RENESAS_RZN1_IRQ_MUX
> +	bool "Renesas RZ/N1 GPIO IRQ multiplexer support"
> +	depends on ARCH_RZN1
> +	select IRQ_DOMAIN
> +	select IRQ_DOMAIN_HIERARCHY
> +	help
> +	  Say yes here to add support for the GPIO IRQ multiplexer embedded
> +	  in Renesas RZ/N1 SoC devices. The GPIO IRQ Muxer selects which of
> +	  the interrupts coming from the GPIO controllers are used.
> +
>  config ST_IRQCHIP
>  	bool
>  	select REGMAP
> diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
> index b822199445ff..b090f84dd42e 100644
> --- a/drivers/irqchip/Makefile
> +++ b/drivers/irqchip/Makefile
> @@ -45,6 +45,7 @@ obj-$(CONFIG_SIRF_IRQ)			+= irq-sirfsoc.o
>  obj-$(CONFIG_JCORE_AIC)			+= irq-jcore-aic.o
>  obj-$(CONFIG_RENESAS_INTC_IRQPIN)	+= irq-renesas-intc-irqpin.o
>  obj-$(CONFIG_RENESAS_IRQC)		+= irq-renesas-irqc.o
> +obj-$(CONFIG_RENESAS_RZN1_IRQ_MUX)	+= rzn1-irq-mux.o
>  obj-$(CONFIG_VERSATILE_FPGA_IRQ)	+= irq-versatile-fpga.o
>  obj-$(CONFIG_ARCH_NSPIRE)		+= irq-zevio.o
>  obj-$(CONFIG_ARCH_VT8500)		+= irq-vt8500.o
> diff --git a/drivers/irqchip/rzn1-irq-mux.c b/drivers/irqchip/rzn1-irq-mux.c
> new file mode 100644
> index 000000000000..767ce67e34d2
> --- /dev/null
> +++ b/drivers/irqchip/rzn1-irq-mux.c
> @@ -0,0 +1,235 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * RZ/N1 GPIO Interrupt Multiplexer
> + *
> + * Copyright (C) 2018 Renesas Electronics Europe Limited
> + *
> + * On RZ/N1 devices, there are 3 Synopsys DesignWare GPIO blocks each configured
> + * to have 32 interrupt outputs, so we have a total of 96 GPIO interrupts.
> + * All of these are passed to the GPIO IRQ Muxer, which selects 8 of the GPIO
> + * interrupts to pass onto the GIC.
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/irqchip/chained_irq.h>
> +#include <linux/irqdomain.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of_irq.h>
> +#include <linux/of_platform.h>
> +
> +#define GPIO_IRQ_SPEC_SIZE	3
> +#define MAX_NR_GPIO_CONTROLLERS	3
> +#define MAX_NR_GPIO_IRQ		32
> +#define MAX_NR_INPUT_IRQS	(MAX_NR_GPIO_CONTROLLERS * MAX_NR_GPIO_IRQ)
> +#define MAX_NR_OUTPUT_IRQS	8
> +
> +struct irqmux_priv;
> +struct irqmux_one {
> +	unsigned int mapped_irq;
> +	unsigned int input_irq_nr;
> +	struct irqmux_priv *priv;
> +};
> +
> +struct irqmux_priv {
> +	struct device *dev;
> +	struct irq_chip irq_chip;

Do we really need this to be per-device? See below.

> +	struct irq_domain *irq_domain;
> +	unsigned int nr_irqs;
> +	struct irqmux_one irq[MAX_NR_OUTPUT_IRQS];
> +};
> +
> +static void irqmux_handler(struct irq_desc *desc)
> +{
> +	struct irq_chip *chip = irq_desc_get_chip(desc);
> +	struct irqmux_one *girq = irq_desc_get_handler_data(desc);
> +	struct irqmux_priv *priv = girq->priv;
> +	unsigned int irq;
> +
> +	chained_irq_enter(chip, desc);
> +
> +	irq = irq_find_mapping(priv->irq_domain, girq->input_irq_nr);
> +	generic_handle_irq(irq);

No error handling? See below again, as I think this outline a
fundamental flaw in the driver.

> +
> +	chained_irq_exit(chip, desc);
> +}
> +
> +static int irqmux_domain_map(struct irq_domain *h, unsigned int irq,
> +			     irq_hw_number_t hwirq)
> +{
> +	struct irqmux_priv *priv = h->host_data;
> +
> +	irq_set_chip_data(irq, h->host_data);
> +	irq_set_chip_and_handler(irq, &priv->irq_chip, handle_simple_irq);
> +
> +	return 0;
> +}
> +
> +static const struct irq_domain_ops irqmux_domain_ops = {
> +	.map	= irqmux_domain_map,
> +};
> +
> +static int irqmux_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct device_node *np = dev->of_node;
> +	struct resource *res;
> +	u32 __iomem *regs;
> +	struct irqmux_priv *priv;
> +	u32 int_specs[MAX_NR_OUTPUT_IRQS][GPIO_IRQ_SPEC_SIZE];
> +	DECLARE_BITMAP(irqs_in_used, MAX_NR_INPUT_IRQS);
> +	unsigned int irqs_out_used = 0;
> +	unsigned int i;
> +	int nr_irqs;
> +	int ret;
> +
> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->dev = dev;
> +	platform_set_drvdata(pdev, priv);
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	regs = devm_ioremap_resource(dev, res);
> +	if (IS_ERR(regs))
> +		return PTR_ERR(regs);
> +
> +	nr_irqs = of_irq_count(np);
> +	if (nr_irqs < 0)
> +		return nr_irqs;
> +
> +	if (nr_irqs > MAX_NR_OUTPUT_IRQS) {
> +		dev_err(dev, "too many output interrupts\n");
> +		return -ENOENT;
> +	}
> +
> +	priv->nr_irqs = nr_irqs;
> +
> +	/* Get the interrupt specifers */
> +	if (of_property_read_u32_array(dev->of_node, "interrupts",
> +				       (u32 *)int_specs,
> +				       priv->nr_irqs * GPIO_IRQ_SPEC_SIZE)) {
> +		dev_err(dev, "cannot get interrupt specifiers\n");
> +		return -ENOENT;
> +	}
> +
> +	bitmap_zero(irqs_in_used, MAX_NR_INPUT_IRQS);
> +
> +	/* Check the interrupt specifiers */
> +	for (i = 0; i < priv->nr_irqs; i++) {
> +		u32 *int_spec = int_specs[i];
> +		u32 input_irq = int_spec[1] * MAX_NR_GPIO_IRQ + int_spec[2];
> +
> +		dev_info(dev, "irq %u=gpio%ua:%u\n", int_spec[0], int_spec[1],
> +			 int_spec[2]);
> +
> +		if (int_spec[0] >= MAX_NR_OUTPUT_IRQS ||
> +		    int_spec[1] >= MAX_NR_GPIO_CONTROLLERS ||
> +		    int_spec[2] >= MAX_NR_GPIO_IRQ) {
> +			dev_err(dev, "invalid interrupt args\n");
> +			return -ENOENT;
> +		}
> +
> +		if (irqs_out_used & BIT(int_spec[0]) ||
> +		    test_bit(input_irq, irqs_in_used)) {
> +			dev_err(dev, "irq %d already used\n", i);
> +			return -ENOENT;
> +		}

I don't think the driver should be in the business of DT validation,
and that you should simply drop this code.

> +
> +		irqs_out_used |= BIT(int_spec[0]);
> +		set_bit(input_irq, irqs_in_used);
> +	}
> +
> +	/* Create IRQ domain for the interrupts coming from the GPIO blocks */
> +	priv->irq_chip.name = dev_name(dev);

OK, that's where I think we have a problem. Your irqchip structure
seem to only be used to display a name?!?

To start with, that's not really the primary use for this object, and
I'd like it to be a single static structure for the whole
driver. Userspace doesn't need to know about the name, so please get
rid of this.

The real issue is that you build the whole thing as a chained
interrupt controller, meaning that nothing controls the masking of the
interrupt. If, as I understand it, this IP is an interrupt router that
selects 8 out of 32 interrupts and passes them onto the GIC, then a
noisy device can just take the whole CPU down by keeping the line
asserted, and SW cannot mask it.

By the look of it, this should be turned into an interrupt hierarchy,
and not a chained interrupt. You do select IRQ_DOMAIN_HIERARCHY, and
completely fail to use the API...

> +	priv->irq_domain = irq_domain_add_linear(np, MAX_NR_INPUT_IRQS,
> +						 &irqmux_domain_ops, priv);
> +	if (!priv->irq_domain)
> +		return -ENOMEM;
> +
> +	/* Setup the interrupts */
> +	for (i = 0; i < priv->nr_irqs; i++) {
> +		struct of_phandle_args ofirq;
> +		u32 *int_spec = int_specs[i];
> +		u32 input_irq = int_spec[1] * MAX_NR_GPIO_IRQ + int_spec[2];
> +		struct irqmux_one *irq = &priv->irq[i];
> +
> +		if (of_irq_parse_one(dev->of_node, i, &ofirq)) {
> +			ret = -ENOENT;
> +			goto err;
> +		}

Why isn't this irq_of_parse_and_map, so that we get rid of the below
create_of_mapping? And if you turn this into a full interrupt
hierarchy, this will completely go away.

> +
> +		priv->irq[i].mapped_irq = irq_create_of_mapping(&ofirq);
> +		if (!priv->irq[i].mapped_irq) {
> +			dev_err(dev, "cannot get interrupt\n");
> +			ret = -ENOENT;
> +			goto err;
> +		}
> +
> +		irq->priv = priv;
> +		irq->input_irq_nr = input_irq;
> +
> +		irq_set_chained_handler_and_data(irq->mapped_irq,
> +						 irqmux_handler, irq);
> +
> +		/* Set up the hardware to pass the interrupt through */
> +		writel(irq->input_irq_nr, &regs[int_spec[0]]);
> +	}
> +
> +	dev_info(dev, "probed, %d gpio interrupts\n", priv->nr_irqs);
> +
> +	return 0;
> +
> +err:
> +	while (i--) {
> +		struct irqmux_one *irq = &priv->irq[i];
> +
> +		irq_set_chained_handler_and_data(irq->mapped_irq, NULL, NULL);
> +		irq_dispose_mapping(irq->mapped_irq);
> +	}
> +	irq_domain_remove(priv->irq_domain);
> +
> +	return 0;
> +}
> +
> +static int irqmux_remove(struct platform_device *pdev)
> +{
> +	struct irqmux_priv *priv = platform_get_drvdata(pdev);
> +	unsigned int i;
> +
> +	for (i = 0; i < priv->nr_irqs; i++) {
> +		struct irqmux_one *irq = &priv->irq[i];
> +
> +		irq_set_chained_handler_and_data(irq->mapped_irq, NULL, NULL);
> +		irq_dispose_mapping(irq->mapped_irq);
> +	}
> +	irq_domain_remove(priv->irq_domain);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id irqmux_match[] = {
> +	{ .compatible = "renesas,rzn1-gpioirqmux", },
> +	{ /* sentinel */ },
> +};
> +
> +MODULE_DEVICE_TABLE(of, irqmux_match);
> +
> +static struct platform_driver irqmux_driver = {
> +	.driver = {
> +		.name = "gpio_irq_mux",
> +		.owner = THIS_MODULE,
> +		.of_match_table = irqmux_match,
> +	},
> +	.probe = irqmux_probe,
> +	.remove = irqmux_remove,
> +};
> +
> +module_platform_driver(irqmux_driver);
> +
> +MODULE_DESCRIPTION("Renesas RZ/N1 GPIO IRQ Multiplexer Driver");
> +MODULE_AUTHOR("Phil Edworthy <phil.edworthy@...esas.com>");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.17.1
> 

To sum it up, I think the structure of this driver is flawed. Please
turn it into a full hierarchy, or alternatively tell me that I have
the wrong end of the stick!

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.

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