Re: [PATCH v2 3/4] irqchip: Add BCM2835 AUX interrupt controller

[Marc Zyngier <marc.zyngier@arm.com>]

On 12/06/17 15:25, Phil Elwell wrote:
> Devices in the BCM2835 AUX block share a common interrupt line, with a
> register indicating which devices have active IRQs. Expose this as a
> nested interrupt controller to avoid IRQ sharing problems (easily
> observed if UART1 and SPI1/2 are enabled simultaneously).
> 
> Signed-off-by: Phil Elwell <phil@raspberrypi.org>
> ---
>  drivers/irqchip/Makefile          |   2 +-
>  drivers/irqchip/irq-bcm2835-aux.c | 155 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 156 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/irqchip/irq-bcm2835-aux.c
> 
> diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
> index b64c59b..cf01920 100644
> --- a/drivers/irqchip/Makefile
> +++ b/drivers/irqchip/Makefile
> @@ -3,7 +3,7 @@ obj-$(CONFIG_IRQCHIP)			+= irqchip.o
>  obj-$(CONFIG_ALPINE_MSI)		+= irq-alpine-msi.o
>  obj-$(CONFIG_ATH79)			+= irq-ath79-cpu.o
>  obj-$(CONFIG_ATH79)			+= irq-ath79-misc.o
> -obj-$(CONFIG_ARCH_BCM2835)		+= irq-bcm2835.o
> +obj-$(CONFIG_ARCH_BCM2835)		+= irq-bcm2835.o irq-bcm2835-aux.o
>  obj-$(CONFIG_ARCH_BCM2835)		+= irq-bcm2836.o
>  obj-$(CONFIG_ARCH_EXYNOS)		+= exynos-combiner.o
>  obj-$(CONFIG_FARADAY_FTINTC010)		+= irq-ftintc010.o
> diff --git a/drivers/irqchip/irq-bcm2835-aux.c b/drivers/irqchip/irq-bcm2835-aux.c
> new file mode 100644
> index 0000000..545f12e
> --- /dev/null
> +++ b/drivers/irqchip/irq-bcm2835-aux.c
> @@ -0,0 +1,155 @@
> +/*
> + * Copyright (C) 2017 Raspberry Pi (Trading) Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/interrupt.h>
> +#include <linux/irqdomain.h>
> +#include <linux/module.h>
> +#include <linux/of_irq.h>
> +#include <linux/platform_device.h>
> +#include <dt-bindings/interrupt-controller/bcm2835-aux-intc.h>
> +
> +#define BCM2835_AUXIRQ		0x00
> +
> +#define BCM2835_AUX_IRQ_UART_MASK BIT(BCM2835_AUX_IRQ_UART)
> +#define BCM2835_AUX_IRQ_SPI1_MASK BIT(BCM2835_AUX_IRQ_SPI1)
> +#define BCM2835_AUX_IRQ_SPI2_MASK BIT(BCM2835_AUX_IRQ_SPI2)
> +
> +#define BCM2835_AUX_IRQ_ALL_MASK \
> +	(BCM2835_AUX_IRQ_UART_MASK | \
> +	 BCM2835_AUX_IRQ_SPI1_MASK | \
> +	 BCM2835_AUX_IRQ_SPI2_MASK)
> +
> +struct aux_irq_state {
> +	void __iomem      *status;
> +	struct irq_domain *domain;
> +};
> +
> +static struct aux_irq_state aux_irq __read_mostly;
> +
> +static irqreturn_t bcm2835_aux_irq_handler(int irq, void *dev_id)
> +{
> +	u32 stat = readl_relaxed(aux_irq.status);
> +
> +	if (stat & BCM2835_AUX_IRQ_UART_MASK)
> +		generic_handle_irq(irq_linear_revmap(aux_irq.domain,
> +						     BCM2835_AUX_IRQ_UART));
> +
> +	if (stat & BCM2835_AUX_IRQ_SPI1_MASK)
> +		generic_handle_irq(irq_linear_revmap(aux_irq.domain,
> +						     BCM2835_AUX_IRQ_SPI1));
> +
> +	if (stat & BCM2835_AUX_IRQ_SPI2_MASK)
> +		generic_handle_irq(irq_linear_revmap(aux_irq.domain,
> +						     BCM2835_AUX_IRQ_SPI2));
> +
> +	return (stat & BCM2835_AUX_IRQ_ALL_MASK) ? IRQ_HANDLED : IRQ_NONE;

I could understand the use of a normal interrupt handler instead of a
chained handler, as the HW doesn't have any way of masking interrupts
(whoever designed this should be forced to fix each and every SoC with a
magnifier and a tiny drill) if it wasn't for this last line.

Here, you're making sure that you always return IRQ_HANDLED if something
was pending, irrespective of whether it has been handled or not. How do
you recover when you have a screaming interrupt and no handler?

Why don't you simply request the interrupt as a shared one, and check
for the state in the handlers themselves? This way, the kernel will be
able to recover from a screaming interrupt by disabling it.

> +}
> +
> +static int bcm2835_aux_irq_xlate(struct irq_domain *d,
> +				 struct device_node *ctrlr,
> +				 const u32 *intspec, unsigned int intsize,
> +				 unsigned long *out_hwirq,
> +				 unsigned int *out_type)
> +{
> +	if (WARN_ON(intsize != 1))
> +		return -EINVAL;
> +
> +	if (WARN_ON(intspec[0] >= BCM2835_AUX_IRQ_COUNT))
> +		return -EINVAL;
> +
> +	*out_hwirq = intspec[0];
> +	*out_type = IRQ_TYPE_NONE;
> +
> +	return 0;
> +}
> +
> +/*
> + * The irq_mask and irq_unmask function pointers are used without
> + * validity checks, so they must not be NULL. Create a dummy function
> + * with the expected type for use as a no-op.
> + */
> +static void bcm2835_aux_irq_dummy(struct irq_data *data)
> +{
> +}
> +
> +static struct irq_chip bcm2835_aux_irq_chip = {
> +	.name = "bcm2835-aux_irq",
> +	.irq_mask = bcm2835_aux_irq_dummy,
> +	.irq_unmask = bcm2835_aux_irq_dummy,
> +};
> +
> +static const struct irq_domain_ops bcm2835_aux_irq_ops = {
> +	.xlate = bcm2835_aux_irq_xlate
> +};
> +
> +static int bcm2835_aux_irq_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct device_node *node = dev->of_node;
> +	int parent_irq;
> +	struct resource *res;
> +	void __iomem *reg;
> +	int i;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	reg = devm_ioremap_resource(dev, res);
> +	if (IS_ERR(reg))
> +		return PTR_ERR(reg);
> +
> +	parent_irq = irq_of_parse_and_map(node, 0);
> +	if (!parent_irq)
> +		return -ENXIO;
> +
> +	aux_irq.status = reg + BCM2835_AUXIRQ;
> +	aux_irq.domain = irq_domain_add_linear(node,
> +					       BCM2835_AUX_IRQ_COUNT,
> +					       &bcm2835_aux_irq_ops,
> +					       NULL);
> +	if (!aux_irq.domain)
> +		return -ENXIO;
> +
> +	for (i = 0; i < BCM2835_AUX_IRQ_COUNT; i++) {
> +		unsigned int irq = irq_create_mapping(aux_irq.domain, i);
> +
> +		if (irq == 0)
> +			return -ENXIO;
> +
> +		irq_set_chip_and_handler(irq, &bcm2835_aux_irq_chip,
> +					 handle_level_irq);
> +	}

My initial question notwithstanding, why do you need any of this? This
should be done at map time, and the irq_create_mapping() call should
entirely be driven from DT.

> +
> +	return  devm_request_irq(dev, parent_irq, bcm2835_aux_irq_handler,
> +				 0, "bcm2835-aux-intc", NULL);
> +}
> +
> +static const struct of_device_id bcm2835_aux_irq_of_match[] = {
> +	{ .compatible = "brcm,bcm2835-aux-intc", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, bcm2835_aux_irq_of_match);
> +
> +static struct platform_driver bcm2835_aux_irq_driver = {
> +	.driver = {
> +		.name = "bcm2835-aux-intc",
> +		.of_match_table = bcm2835_aux_irq_of_match,
> +	},
> +	.probe          = bcm2835_aux_irq_probe,
> +};
> +builtin_platform_driver(bcm2835_aux_irq_driver);
> +
> +MODULE_AUTHOR("Phil Elwell <phil@raspberrypi.org>");
> +MODULE_DESCRIPTION("BCM2835 auxiliary peripheral interrupt driver");
> +MODULE_LICENSE("GPL v2");
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...