Date:   Wed, 11 Oct 2017 18:35:42 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Andreas Färber <afaerber@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, Roc He <hepeng@...oo.tv>,
        蒋丽琴 <jiang.liqin@...iatech.com>
Subject: Re: [PATCH v2 2/3] irqchip: Add Realtek RTD1295 mux driver

On 28/08/17 11:53, Andreas Färber wrote:
> This irq mux driver is derived from the RTD1295 vendor DT and assumes a
> linear mapping between intr_en and intr_status registers.
> Code for RTD119x indicates this may not always be the case (i2c_3).
> 
> Based in part on QNAP's arch/arm/mach-rtk119x/rtk_irq_mux.c code.
> 
> Signed-off-by: Andreas Färber <afaerber@...e.de>
> ---
>  v1 -> v2:
>  * Renamed struct fields to avoid ambiguity (Marc)
>  * Refactored offset lookup to avoid per-compatible init functions
>  * Inserted white lines to clarify balanced locking (Marc)
>  * Dropped forwarding of set_affinity to GIC (Marc)
>  * Added spinlocks for consistency (Marc)
>  * Limited initialization quirk to iso mux
>  * Fixed spinlock initialization (Andrew)
>  
>  drivers/irqchip/Makefile          |   1 +
>  drivers/irqchip/irq-rtd119x-mux.c | 204 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 205 insertions(+)
>  create mode 100644 drivers/irqchip/irq-rtd119x-mux.c
> 
> diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
> index e88d856cc09c..46202a0b7d96 100644
> --- a/drivers/irqchip/Makefile
> +++ b/drivers/irqchip/Makefile
> @@ -78,3 +78,4 @@ obj-$(CONFIG_EZNPS_GIC)			+= irq-eznps.o
>  obj-$(CONFIG_ARCH_ASPEED)		+= irq-aspeed-vic.o irq-aspeed-i2c-ic.o
>  obj-$(CONFIG_STM32_EXTI) 		+= irq-stm32-exti.o
>  obj-$(CONFIG_QCOM_IRQ_COMBINER)		+= qcom-irq-combiner.o
> +obj-$(CONFIG_ARCH_REALTEK)		+= irq-rtd119x-mux.o
> diff --git a/drivers/irqchip/irq-rtd119x-mux.c b/drivers/irqchip/irq-rtd119x-mux.c
> new file mode 100644
> index 000000000000..65d22e163bef
> --- /dev/null
> +++ b/drivers/irqchip/irq-rtd119x-mux.c
> @@ -0,0 +1,204 @@
> +/*
> + * Realtek RTD129x IRQ mux
> + *
> + * Copyright (c) 2017 Andreas Färber
> + *
> + * SPDX-License-Identifier: GPL-2.0+
> + */
> +
> +#include <linux/io.h>
> +#include <linux/irqchip.h>
> +#include <linux/irqchip/chained_irq.h>
> +#include <linux/irqdomain.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +#include <linux/slab.h>
> +
> +struct rtd119x_irq_mux_info {
> +	unsigned intr_status_offset;
> +	unsigned intr_en_offset;
> +};
> +
> +struct rtd119x_irq_mux_data {
> +	void __iomem *intr_status;
> +	void __iomem *intr_en;
> +	int irq;
> +	struct irq_domain *domain;
> +	spinlock_t lock;
> +};
> +
> +static void rtd119x_mux_irq_handle(struct irq_desc *desc)
> +{
> +	struct rtd119x_irq_mux_data *data = irq_desc_get_handler_data(desc);
> +	struct irq_chip *chip = irq_desc_get_chip(desc);
> +	u32 intr_en, intr_status, status;
> +	int ret;
> +
> +	chained_irq_enter(chip, desc);
> +
> +	spin_lock(&data->lock);
> +	intr_en     = readl(data->intr_en);

I think that all the MMIO accessors in this file can advantageously
turned into their _relaxed version (none of them require any barrier).

> +	intr_status = readl(data->intr_status);
> +	spin_unlock(&data->lock);
> +
> +	status = intr_status & intr_en;
> +	if (status != 0) {
> +		unsigned irq = __ffs(status);
> +		ret = generic_handle_irq(irq_find_mapping(data->domain, irq));
> +		if (ret == 0) {
> +			spin_lock(&data->lock);
> +
> +			intr_status = readl(data->intr_status);
> +			intr_status |= BIT(irq - 1);
> +			writel(intr_status, data->intr_status);

This sequence feels a bit wrong: It seems to imply that writing to the
status register is a way to EOI the interrupt. But what happens to the
other bits that you've read? I fear that you are inadvertently
signalling an EOI for interrupts that you may not have handled yet.

I'd rather see something like this:

	while (status) {
		irq = __ffs(status) - 1;
		writel_relaxed(BIT(irq), data->intr_status);
		generic_handle_irq(irq_find_mapping(data->domain, irq));
		status &= ~irq;
	}

assuming I've understood how the HW works. No need for additional locking.

> +
> +			spin_unlock(&data->lock);
> +		}
> +	}
> +
> +	chained_irq_exit(chip, desc);
> +}
> +
> +static void rtd119x_mux_mask_irq(struct irq_data *data)
> +{
> +	struct rtd119x_irq_mux_data *mux_data = irq_data_get_irq_chip_data(data);
> +	u32 intr_status;
> +
> +	spin_lock(&mux_data->lock);

Bang, you're dead. If you get the chained interrupt firing here on the
same CPU, it will take the lock in the above function, and everything
will grind to a halt. Use the irqsave version.

> +
> +	intr_status = readl(mux_data->intr_status);
> +	intr_status |= BIT(data->hwirq);
> +	writel(intr_status, mux_data->intr_status);

Or maybe I haven't understood how this works at all. Can you please
explain? I'd expect masking to be the opposite of unmasking, but that's
not the case...

> +
> +	spin_unlock(&mux_data->lock);
> +}
> +
> +static void rtd119x_mux_unmask_irq(struct irq_data *data)
> +{
> +	struct rtd119x_irq_mux_data *mux_data = irq_data_get_irq_chip_data(data);
> +	u32 intr_en;
> +
> +	spin_lock(&mux_data->lock);
> +

Same here.

> +	intr_en = readl(mux_data->intr_en);
> +	intr_en |= BIT(data->hwirq);
> +	writel(intr_en, mux_data->intr_en);
> +
> +	spin_unlock(&mux_data->lock);
> +}
> +
> +static int rtd119x_mux_set_affinity(struct irq_data *d,
> +			const struct cpumask *mask_val, bool force)
> +{
> +	/* Forwarding the affinity to the parent would affect all 32 interrupts. */
> +	return -EINVAL;
> +}
> +
> +static struct irq_chip rtd119x_mux_irq_chip = {
> +	.name			= "rtd119x-mux",
> +	.irq_mask		= rtd119x_mux_mask_irq,
> +	.irq_unmask		= rtd119x_mux_unmask_irq,
> +	.irq_set_affinity	= rtd119x_mux_set_affinity,
> +};
> +
> +static int rtd119x_mux_irq_domain_map(struct irq_domain *d,
> +		unsigned int irq, irq_hw_number_t hw)
> +{
> +	struct rtd119x_irq_mux_data *data = d->host_data;
> +
> +	irq_set_chip_and_handler(irq, &rtd119x_mux_irq_chip, handle_level_irq);
> +	irq_set_chip_data(irq, data);
> +	irq_set_probe(irq);
> +
> +	return 0;
> +}
> +
> +static struct irq_domain_ops rtd119x_mux_irq_domain_ops = {
> +	.xlate	= irq_domain_xlate_onecell,
> +	.map	= rtd119x_mux_irq_domain_map,
> +};
> +
> +static const struct rtd119x_irq_mux_info rtd1295_iso_irq_mux_info = {
> +	.intr_status_offset	= 0x0,
> +	.intr_en_offset		= 0x40,
> +};
> +
> +static const struct rtd119x_irq_mux_info rtd1295_irq_mux_info = {
> +	.intr_status_offset	= 0xc,
> +	.intr_en_offset		= 0x80,
> +};
> +
> +static const struct of_device_id rtd1295_irq_mux_dt_matches[] = {
> +	{
> +		.compatible = "realtek,rtd1295-iso-irq-mux",
> +		.data = &rtd1295_iso_irq_mux_info,
> +	}, {
> +		.compatible = "realtek,rtd1295-irq-mux",
> +		.data = &rtd1295_irq_mux_info,
> +	}, {
> +	}
> +};
> +
> +static int __init rtd119x_irq_mux_init(struct device_node *node,
> +				       struct device_node *parent)
> +{
> +	struct rtd119x_irq_mux_data *data;
> +	const struct of_device_id *match;
> +	const struct rtd119x_irq_mux_info *info;
> +	void __iomem *base;
> +	u32 val;
> +
> +	match = of_match_node(rtd1295_irq_mux_dt_matches, node);
> +	if (!match)
> +		return -EINVAL;
> +
> +	info = match->data;
> +	if (!info)
> +		return -EINVAL;
> +
> +	base = of_iomap(node, 0);
> +	if (IS_ERR(base))
> +		return PTR_ERR(base);
> +
> +	data = kzalloc(sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->intr_status = base + info->intr_status_offset;
> +	data->intr_en     = base + info->intr_en_offset;
> +
> +	data->irq = irq_of_parse_and_map(node, 0);
> +	if (data->irq <= 0) {
> +		kfree(data);
> +		return -EINVAL;
> +	}
> +
> +	spin_lock_init(&data->lock);
> +
> +	data->domain = irq_domain_add_linear(node, 32,
> +				&rtd119x_mux_irq_domain_ops, data);
> +	if (!data->domain) {
> +		kfree(data);
> +		return -ENOMEM;
> +	}
> +
> +	if (of_device_is_compatible(node, "realtek,rtd1295-iso-irq-mux")) {
> +		const int uart0_irq = 2;
> +
> +		spin_lock(&data->lock);
> +
> +		val = readl(data->intr_en);
> +		val &= ~BIT(uart0_irq);
> +		writel(val, data->intr_en);
> +
> +		writel(BIT(uart0_irq), data->intr_status);

Same here. Can you please explain what you're trying to do? The locking
seems a bit pointless (nobody can request the interrupt yet), and this
uart0 needs at least a comment, and maybe a description in the device-tree.

> +
> +		spin_unlock(&data->lock);
> +	}
> +
> +	irq_set_chained_handler_and_data(data->irq, rtd119x_mux_irq_handle, data);
> +
> +	return 0;
> +}
> +IRQCHIP_DECLARE(rtd1295_iso_mux, "realtek,rtd1295-iso-irq-mux", rtd119x_irq_mux_init);
> +IRQCHIP_DECLARE(rtd1295_mux, "realtek,rtd1295-irq-mux", rtd119x_irq_mux_init);
> 

Thanks,

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

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