linux arm irq (4): interrupt driver interface

合集 - arm linux中断(4)

1.linux arm irq (1): irq init2021-05-172.linux arm irq (2): interrupt handling2021-05-173.linux arm irq (3): gpio interrupt2021-05-17

4.linux arm irq (4): interrupt driver interface2021-05-17

收起

linux arm irq (4)

4 interrupt driver interface

Author: Yangkai Wang
wang_yangkai@163.com
Coding in 2021/05/16
转载请注明author,出处.

linux version 3.4.39
s5p6818 soc

Cortex-A53 Octa core CPU
Interrupt Controller，GIC400

GIC (Generic Interrupt Controllers), reference:Arm Generic Interrupt Controller Architecture version 2.0,Architecture Specification

GPIO controller，reference:S5P6818 Application Processor Datasheet

• include <linux/interrupt.h>

static inline int __must_check
request_irq(unsigned int irq, irq_handler_t handler, unsigned long flags,
	    const char *name, void *dev)
{
	return request_threaded_irq(irq, handler, NULL, flags, name, dev);
}

extern void disable_irq_nosync(unsigned int irq);
extern void disable_irq(unsigned int irq);
extern void enable_irq(unsigned int irq);

etc.

example code:

/*
#define CFG_KEYPAD_KEY_OK				{ PAD_GPIO_B + 31 }
#define CFG_KEYPAD_KEY_OK_CODE				{ KEY_OK } /* 352 */
*/

/* drivers/input/keyboard/nxp_io_key.c */
...
static int nxp_key_probe(struct platform_device *pdev)
{
        ...

		printk("~~~ %s() gpio:%d, irqno:%d, call request_irq()\n", \
			__func__, code->io, gpio_to_irq(code->io));
		ret = request_irq(gpio_to_irq(code->io), nxp_key_irqhnd,
					(IRQF_SHARED | IRQ_TYPE_EDGE_BOTH), pdev->name, code);
		if (ret) {
			pr_err("fail, gpio[%d] %s request irq...\n", code->io, pdev->name);
			goto err_irq;
		}
		printk("~~~ %s() gpio:%d, irqno:%d, call disable_irq()\n", \
			__func__, code->io, gpio_to_irq(code->io));
		disable_irq(gpio_to_irq(code->io));
		printk("~~~ %s() gpio:%d, irqno:%d, call enable_irq()\n", \
			__func__, code->io, gpio_to_irq(code->io));	
		enable_irq(gpio_to_irq(code->io));
		printk("~~~ %s() gpio:%d, irqno:%d, call disable_irq()\n", \
			__func__, code->io, gpio_to_irq(code->io));
		disable_irq(gpio_to_irq(code->io));
		printk("~~~ %s() gpio:%d, irqno:%d, call enable_irq()\n", \
			__func__, code->io, gpio_to_irq(code->io));	
		enable_irq(gpio_to_irq(code->io));
...
}
...
static irqreturn_t nxp_key_irqhnd(int irqno, void *dev_id)
{
	struct key_code *code = dev_id;

	printk("~~~ %s() irqno:%d\n", __func__, irqno);

	queue_delayed_work(code->kcode_wq,
				&code->kcode_work, DELAY_WORK_JIFFIES);

	return IRQ_HANDLED;
}
...

log

[    1.688000] ~~~ nxp_key_probe() gpio:63, irqno:169, call request_irq()
[    1.692000] gpio_set_type_irq: gpio irq = 169, GPIOB.31, type=0x3
[    1.692000] reg=0xf001b00c, val=0x00000000
[    1.692000] reg=0xf001b028, val=0x80000000
[    1.692000] reg=0xf001b024, val=0x55550002
[    1.692000] ~~~ __setup_irq() irq:169, desc->depth:1, call irq_startup()
[    1.692000] ~~~ irq_startup() irq:169, call irq_enable()
[    1.692000] gpio_irq_enable: gpio irq = 169, GPIOB.31
[    1.692000] ~~~ gpio_irq_enable() gpio irq:169, GPIOB.31

[    1.720000] ~~~ nxp_key_probe() gpio:63, irqno:169, call disable_irq()
[    1.724000] gpio_irq_disable: gpio irq = 169, GPIOB.31
[    1.724000] ~~~ gpio_irq_disable() gpio irq:169, GPIOB.31
[    1.736000] ~~~ nxp_key_probe() gpio:63, irqno:169, call enable_irq()
[    1.740000] ~~~ __enable_irq() do, irq:169, desc->depth:1
[    1.740000] gpio_irq_enable: gpio irq = 169, GPIOB.31
[    1.740000] ~~~ gpio_irq_enable() gpio irq:169, GPIOB.31
[    1.740000] ~~~ __enable_irq() done, irq:169, desc->depth:0
[    1.760000] ~~~ nxp_key_probe() gpio:63, irqno:169, call disable_irq()
[    1.764000] gpio_irq_disable: gpio irq = 169, GPIOB.31
[    1.764000] ~~~ gpio_irq_disable() gpio irq:169, GPIOB.31
[    1.776000] ~~~ nxp_key_probe() gpio:63, irqno:169, call enable_irq()
[    1.784000] ~~~ __enable_irq() do, irq:169, desc->depth:1
[    1.784000] gpio_irq_enable: gpio irq = 169, GPIOB.31
[    1.784000] ~~~ gpio_irq_enable() gpio irq:169, GPIOB.31
[    1.784000] ~~~ __enable_irq() done, irq:169, desc->depth:0
[    1.800000] [1] key io= 63, code= 352

• gpio_to_irq

/* arch/arm/include/asm/gpio.h */

#ifndef _ARCH_ARM_GPIO_H
#define _ARCH_ARM_GPIO_H

#if CONFIG_ARCH_NR_GPIO > 0
#define ARCH_NR_GPIOS CONFIG_ARCH_NR_GPIO
#endif

/* not all ARM platforms necessarily support this API ... */
#include <mach/gpio.h>

#ifndef __ARM_GPIOLIB_COMPLEX
/* Note: this may rely upon the value of ARCH_NR_GPIOS set in mach/gpio.h */
#include <asm-generic/gpio.h>

/* The trivial gpiolib dispatchers */
#define gpio_get_value  __gpio_get_value
#define gpio_set_value  __gpio_set_value
#define gpio_cansleep   __gpio_cansleep
#endif

/*
 * Provide a default gpio_to_irq() which should satisfy every case.
 * However, some platforms want to do this differently, so allow them
 * to override it.
 */
#ifndef gpio_to_irq
#define gpio_to_irq	__gpio_to_irq
#endif

#endif /* _ARCH_ARM_GPIO_H */

/* drivers/gpio/gpiolib.c */

/**
 * __gpio_to_irq() - return the IRQ corresponding to a GPIO
 * @gpio: gpio whose IRQ will be returned (already requested)
 * Context: any
 *
 * This is used directly or indirectly to implement gpio_to_irq().
 * It returns the number of the IRQ signaled by this (input) GPIO,
 * or a negative errno.
 */
int __gpio_to_irq(unsigned gpio)
{
	struct gpio_chip	*chip;

	chip = gpio_to_chip(gpio);
	return chip->to_irq ? chip->to_irq(chip, gpio - chip->base) : -ENXIO;
}
EXPORT_SYMBOL_GPL(__gpio_to_irq);

/* drivers/gpio/gpio-nxp.c */

static int nxp_gpio_to_irq( struct gpio_chip *chip , unsigned offset )
{
	struct nxp_gpio *gpio = GET_GPIO(chip);
	unsigned int io = gpio->index * GPIO_NUM_PER_BANK + offset;

	/*printk("~~~ %s() offset:%d, io:%d, irq:%d\n", __func__, \
			offset, io, io + IRQ_GPIO_START);*/

	return (io + IRQ_GPIO_START);
}

io number to irq number: fixed io number + IRQ_GPIO_START;


linux 3.4.39 s5p6818, irq number都是固定分配好的；reference:arch/arm/mach-s5p6818/include/mach/s5p6818_irq.h

• request_irq()

/* include/linux/interrupt.h */

static inline int __must_check
request_irq(unsigned int irq, irq_handler_t handler, unsigned long flags,
	    const char *name, void *dev)
{
	return request_threaded_irq(irq, handler, NULL, flags, name, dev);
}

/* kernel/irq/manage.c */

/**
 *	request_threaded_irq - allocate an interrupt line
 *	@irq: Interrupt line to allocate
 *	@handler: Function to be called when the IRQ occurs.
 *		  Primary handler for threaded interrupts
 *		  If NULL and thread_fn != NULL the default
 *		  primary handler is installed
 *	@thread_fn: Function called from the irq handler thread
 *		    If NULL, no irq thread is created
 *	@irqflags: Interrupt type flags
 *	@devname: An ascii name for the claiming device
 *	@dev_id: A cookie passed back to the handler function
 *
 *	This call allocates interrupt resources and enables the
 *	interrupt line and IRQ handling. From the point this
 *	call is made your handler function may be invoked. Since
 *	your handler function must clear any interrupt the board
 *	raises, you must take care both to initialise your hardware
 *	and to set up the interrupt handler in the right order.
 *
 *	If you want to set up a threaded irq handler for your device
 *	then you need to supply @handler and @thread_fn. @handler is
 *	still called in hard interrupt context and has to check
 *	whether the interrupt originates from the device. If yes it
 *	needs to disable the interrupt on the device and return
 *	IRQ_WAKE_THREAD which will wake up the handler thread and run
 *	@thread_fn. This split handler design is necessary to support
 *	shared interrupts.
 *
 *	Dev_id must be globally unique. Normally the address of the
 *	device data structure is used as the cookie. Since the handler
 *	receives this value it makes sense to use it.
 *
 *	If your interrupt is shared you must pass a non NULL dev_id
 *	as this is required when freeing the interrupt.
 *
 *	Flags:
 *
 *	IRQF_SHARED		Interrupt is shared
 *	IRQF_TRIGGER_*		Specify active edge(s) or level
 *
 */
int request_threaded_irq(unsigned int irq, irq_handler_t handler,
			 irq_handler_t thread_fn, unsigned long irqflags,
			 const char *devname, void *dev_id)
{
	struct irqaction *action;
	struct irq_desc *desc;
	int retval;

	/*
	 * Sanity-check: shared interrupts must pass in a real dev-ID,
	 * otherwise we'll have trouble later trying to figure out
	 * which interrupt is which (messes up the interrupt freeing
	 * logic etc).
	 */
	if ((irqflags & IRQF_SHARED) && !dev_id)
		return -EINVAL;

	desc = irq_to_desc(irq);
	if (!desc)
		return -EINVAL;

	if (!irq_settings_can_request(desc) ||
	    WARN_ON(irq_settings_is_per_cpu_devid(desc)))
		return -EINVAL;

	if (!handler) {
		if (!thread_fn)
			return -EINVAL;
		handler = irq_default_primary_handler;
	}

	action = kzalloc(sizeof(struct irqaction), GFP_KERNEL);
	if (!action)
		return -ENOMEM;

	action->handler = handler;
	action->thread_fn = thread_fn;
	action->flags = irqflags;
	action->name = devname;
	action->dev_id = dev_id;

	chip_bus_lock(desc);
	retval = __setup_irq(irq, desc, action);
	chip_bus_sync_unlock(desc);

	if (retval)
		kfree(action);

#ifdef CONFIG_DEBUG_SHIRQ_FIXME
	if (!retval && (irqflags & IRQF_SHARED)) {
		/*
		 * It's a shared IRQ -- the driver ought to be prepared for it
		 * to happen immediately, so let's make sure....
		 * We disable the irq to make sure that a 'real' IRQ doesn't
		 * run in parallel with our fake.
		 */
		unsigned long flags;

		disable_irq(irq);
		local_irq_save(flags);

		handler(irq, dev_id);

		local_irq_restore(flags);
		enable_irq(irq);
	}
#endif

	return retval;
}
EXPORT_SYMBOL(request_threaded_irq);

alloc struct irqaction action;
struct irq_desc *desc = irq_to_desc(irq);
retval = __setup_irq(irq, desc, action); / * core ops */

• static int __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)

/*
 * Internal function to register an irqaction - typically used to
 * allocate special interrupts that are part of the architecture.
 */
static int
__setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
{
	struct irqaction *old, **old_ptr;
	const char *old_name = NULL;
	unsigned long flags, thread_mask = 0;
	int ret, nested, shared = 0;
	cpumask_var_t mask;

	if (!desc)
		return -EINVAL;

	if (desc->irq_data.chip == &no_irq_chip)
		return -ENOSYS;
	if (!try_module_get(desc->owner))
		return -ENODEV;

	/*
	 * Check whether the interrupt nests into another interrupt
	 * thread.
	 */
	nested = irq_settings_is_nested_thread(desc);
	if (nested) {
		if (!new->thread_fn) {
			ret = -EINVAL;
			goto out_mput;
		}
		/*
		 * Replace the primary handler which was provided from
		 * the driver for non nested interrupt handling by the
		 * dummy function which warns when called.
		 */
		new->handler = irq_nested_primary_handler;
	} else {
		if (irq_settings_can_thread(desc))
			irq_setup_forced_threading(new);
	}

	/*
	 * Create a handler thread when a thread function is supplied
	 * and the interrupt does not nest into another interrupt
	 * thread.
	 */
	if (new->thread_fn && !nested) {
		struct task_struct *t;

		t = kthread_create(irq_thread, new, "irq/%d-%s", irq,
				   new->name);
		if (IS_ERR(t)) {
			ret = PTR_ERR(t);
			goto out_mput;
		}
		/*
		 * We keep the reference to the task struct even if
		 * the thread dies to avoid that the interrupt code
		 * references an already freed task_struct.
		 */
		get_task_struct(t);
		new->thread = t;
		/*
		 * Tell the thread to set its affinity. This is
		 * important for shared interrupt handlers as we do
		 * not invoke setup_affinity() for the secondary
		 * handlers as everything is already set up. Even for
		 * interrupts marked with IRQF_NO_BALANCE this is
		 * correct as we want the thread to move to the cpu(s)
		 * on which the requesting code placed the interrupt.
		 */
		set_bit(IRQTF_AFFINITY, &new->thread_flags);
	}

	if (!alloc_cpumask_var(&mask, GFP_KERNEL)) {
		ret = -ENOMEM;
		goto out_thread;
	}

	/*
	 * The following block of code has to be executed atomically
	 */
	raw_spin_lock_irqsave(&desc->lock, flags);
	old_ptr = &desc->action;
	old = *old_ptr;
	if (old) {
		/*
		 * Can't share interrupts unless both agree to and are
		 * the same type (level, edge, polarity). So both flag
		 * fields must have IRQF_SHARED set and the bits which
		 * set the trigger type must match. Also all must
		 * agree on ONESHOT.
		 */
		if (!((old->flags & new->flags) & IRQF_SHARED) ||
		    ((old->flags ^ new->flags) & IRQF_TRIGGER_MASK) ||
		    ((old->flags ^ new->flags) & IRQF_ONESHOT)) {
			old_name = old->name;
			goto mismatch;
		}

		/* All handlers must agree on per-cpuness */
		if ((old->flags & IRQF_PERCPU) !=
		    (new->flags & IRQF_PERCPU))
			goto mismatch;

		/* add new interrupt at end of irq queue */
		do {
			/*
			 * Or all existing action->thread_mask bits,
			 * so we can find the next zero bit for this
			 * new action.
			 */
			thread_mask |= old->thread_mask;
			old_ptr = &old->next;
			old = *old_ptr;
		} while (old);
		shared = 1;
	}

	/*
	 * Setup the thread mask for this irqaction for ONESHOT. For
	 * !ONESHOT irqs the thread mask is 0 so we can avoid a
	 * conditional in irq_wake_thread().
	 */
	if (new->flags & IRQF_ONESHOT) {
		/*
		 * Unlikely to have 32 resp 64 irqs sharing one line,
		 * but who knows.
		 */
		if (thread_mask == ~0UL) {
			ret = -EBUSY;
			goto out_mask;
		}
		/*
		 * The thread_mask for the action is or'ed to
		 * desc->thread_active to indicate that the
		 * IRQF_ONESHOT thread handler has been woken, but not
		 * yet finished. The bit is cleared when a thread
		 * completes. When all threads of a shared interrupt
		 * line have completed desc->threads_active becomes
		 * zero and the interrupt line is unmasked. See
		 * handle.c:irq_wake_thread() for further information.
		 *
		 * If no thread is woken by primary (hard irq context)
		 * interrupt handlers, then desc->threads_active is
		 * also checked for zero to unmask the irq line in the
		 * affected hard irq flow handlers
		 * (handle_[fasteoi|level]_irq).
		 *
		 * The new action gets the first zero bit of
		 * thread_mask assigned. See the loop above which or's
		 * all existing action->thread_mask bits.
		 */
		new->thread_mask = 1 << ffz(thread_mask);
	}

	if (!shared) {
		init_waitqueue_head(&desc->wait_for_threads);

		/* Setup the type (level, edge polarity) if configured: */
		if (new->flags & IRQF_TRIGGER_MASK) {
			ret = __irq_set_trigger(desc, irq,
					new->flags & IRQF_TRIGGER_MASK);

			if (ret)
				goto out_mask;
		}

		desc->istate &= ~(IRQS_AUTODETECT | IRQS_SPURIOUS_DISABLED | \
				  IRQS_ONESHOT | IRQS_WAITING);
		irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);

		if (new->flags & IRQF_PERCPU) {
			irqd_set(&desc->irq_data, IRQD_PER_CPU);
			irq_settings_set_per_cpu(desc);
		}

		if (new->flags & IRQF_ONESHOT)
			desc->istate |= IRQS_ONESHOT;

		if (irq_settings_can_autoenable(desc)) {
			printk("~~~ %s() irq:%u, desc->depth:%d, call irq_startup()\n", \
				__func__, irq, desc->depth);
			irq_startup(desc, true);
			/*printk("~~~ %s() irq:%u, desc->depth:%d\n", \
				__func__, irq, desc->depth);*/
		} else {
			/* Undo nested disables: */
			desc->depth = 1;
			printk("~~~ %s() irq:%d, set desc->depth = 1\n", __func__, irq);
		}

		/* Exclude IRQ from balancing if requested */
		if (new->flags & IRQF_NOBALANCING) {
			irq_settings_set_no_balancing(desc);
			irqd_set(&desc->irq_data, IRQD_NO_BALANCING);
		}

		/* Set default affinity mask once everything is setup */
		setup_affinity(irq, desc, mask);

	} else if (new->flags & IRQF_TRIGGER_MASK) {
		unsigned int nmsk = new->flags & IRQF_TRIGGER_MASK;
		unsigned int omsk = irq_settings_get_trigger_mask(desc);

		if (nmsk != omsk)
			/* hope the handler works with current  trigger mode */
			pr_warning("IRQ %d uses trigger mode %u; requested %u\n",
				   irq, nmsk, omsk);
	}

	new->irq = irq;
	*old_ptr = new;

	/* Reset broken irq detection when installing new handler */
	desc->irq_count = 0;
	desc->irqs_unhandled = 0;

	/*
	 * Check whether we disabled the irq via the spurious handler
	 * before. Reenable it and give it another chance.
	 */
	if (shared && (desc->istate & IRQS_SPURIOUS_DISABLED)) {
		desc->istate &= ~IRQS_SPURIOUS_DISABLED;
		__enable_irq(desc, irq, false);
	}

	raw_spin_unlock_irqrestore(&desc->lock, flags);

	/*
	 * Strictly no need to wake it up, but hung_task complains
	 * when no hard interrupt wakes the thread up.
	 */
	if (new->thread)
		wake_up_process(new->thread);

	register_irq_proc(irq, desc);
	new->dir = NULL;
	register_handler_proc(irq, new);
	free_cpumask_var(mask);

	return 0;

mismatch:
#ifdef CONFIG_DEBUG_SHIRQ
	if (!(new->flags & IRQF_PROBE_SHARED)) {
		printk(KERN_ERR "IRQ handler type mismatch for IRQ %d\n", irq);
		if (old_name)
			printk(KERN_ERR "current handler: %s\n", old_name);
		dump_stack();
	}
#endif
	ret = -EBUSY;

out_mask:
	raw_spin_unlock_irqrestore(&desc->lock, flags);
	free_cpumask_var(mask);

out_thread:
	if (new->thread) {
		struct task_struct *t = new->thread;

		new->thread = NULL;
		kthread_stop(t);
		put_task_struct(t);
	}
out_mput:
	module_put(desc->owner);
	return ret;
}

main operation：

old_ptr = &desc->action;
old = *old_ptr;
if (old) {
    /* if irq is share interrupts, and had desc->action */
    ...
    shared = 1;
}

if first times request this irq, shared value is 0;

if (!shared) {
    /* Setup the type (level, edge polarity) if configured: */
	if (new->flags & IRQF_TRIGGER_MASK) {
		ret = __irq_set_trigger(desc, irq,
				new->flags & IRQF_TRIGGER_MASK);
            |
            /* caller masked out all except trigger mode flags */
	        ret = chip->irq_set_type(&desc->irq_data, flags);
	}

	if (irq_settings_can_autoenable(desc)) {
		printk("~~~ %s() irq:%u, desc->depth:%d, call irq_startup()\n", \
			__func__, irq, desc->depth);
		irq_startup(desc, true);
            |
            if (desc->irq_data.chip->irq_startup) {
                /*  */
	        } else {
		        printk("~~~ %s() irq:%u, call irq_enable()\n", \
			        __func__, desc->irq_data.irq);
		        irq_enable(desc);
                
                /* kernel/irq/chip.c
                void irq_enable(struct irq_desc *desc)
                {
	                irq_state_clr_disabled(desc);
	                if (desc->irq_data.chip->irq_enable)
		                desc->irq_data.chip->irq_enable(&desc->irq_data);
	                else
		                desc->irq_data.chip->irq_unmask(&desc->irq_data);
    	            irq_state_clr_masked(desc);
                }
                */

	    }
	}
}

new->irq = irq;
*old_ptr = new;

__irq_set_trigger(desc, irq, new->flags & IRQF_TRIGGER_MASK); call chip->irq_set_type(&desc->irq_data, flags);
irq_startup(desc, true); call irq_enable(desc);
and
setup &desc->action; desc->action = new;

• void disable_irq(unsigned int irq)

/* kernel/irq/manage.c */

/**
 *	disable_irq - disable an irq and wait for completion
 *	@irq: Interrupt to disable
 *
 *	Disable the selected interrupt line.  Enables and Disables are
 *	nested.
 *	This function waits for any pending IRQ handlers for this interrupt
 *	to complete before returning. If you use this function while
 *	holding a resource the IRQ handler may need you will deadlock.
 *
 *	This function may be called - with care - from IRQ context.
 */
void disable_irq(unsigned int irq)
{
	if (!__disable_irq_nosync(irq))
		synchronize_irq(irq);
}
EXPORT_SYMBOL(disable_irq);

Enables and Disables are nested.
If you use this function while holding a resource the IRQ handler may need you will deadlock.

/* kernel/irq/manage.c */

static int __disable_irq_nosync(unsigned int irq)
{
	unsigned long flags;
	struct irq_desc *desc = irq_get_desc_buslock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);

	if (!desc)
		return -EINVAL;
	__disable_irq(desc, irq, false);
	irq_put_desc_busunlock(desc, flags);
	return 0;
}

/* kernel/irq/manage.c */

void __disable_irq(struct irq_desc *desc, unsigned int irq, bool suspend)
{
	if (suspend) {
		if (!desc->action || (desc->action->flags & IRQF_NO_SUSPEND))
			return;
		desc->istate |= IRQS_SUSPENDED;
	}

	/*printk("~~~ %s() irq:%d, desc->depth:%d\n", __func__, \
		irq, desc->depth);*/
	if (!desc->depth++)
		irq_disable(desc);
}

/* kernel/irq/chip.c */

void irq_disable(struct irq_desc *desc)
{
	irq_state_set_disabled(desc);
	if (desc->irq_data.chip->irq_disable) {
		desc->irq_data.chip->irq_disable(&desc->irq_data);
		irq_state_set_masked(desc);
	}
}

/* kernel/irq/manage.c */

/**
 *	synchronize_irq - wait for pending IRQ handlers (on other CPUs)
 *	@irq: interrupt number to wait for
 *
 *	This function waits for any pending IRQ handlers for this interrupt
 *	to complete before returning. If you use this function while
 *	holding a resource the IRQ handler may need you will deadlock.
 *
 *	This function may be called - with care - from IRQ context.
 */
void synchronize_irq(unsigned int irq)
{
	struct irq_desc *desc = irq_to_desc(irq);
	bool inprogress;

	if (!desc)
		return;

	do {
		unsigned long flags;

		/*
		 * Wait until we're out of the critical section.  This might
		 * give the wrong answer due to the lack of memory barriers.
		 */
		while (irqd_irq_inprogress(&desc->irq_data))
			cpu_relax();

		/* Ok, that indicated we're done: double-check carefully. */
		raw_spin_lock_irqsave(&desc->lock, flags);
		inprogress = irqd_irq_inprogress(&desc->irq_data);
		raw_spin_unlock_irqrestore(&desc->lock, flags);

		/* Oops, that failed? */
	} while (inprogress);

	/*
	 * We made sure that no hardirq handler is running. Now verify
	 * that no threaded handlers are active.
	 */
	wait_event(desc->wait_for_threads, !atomic_read(&desc->threads_active));
}
EXPORT_SYMBOL(synchronize_irq);

This function waits for any pending IRQ handlers for this interrupt to complete before returning. If you use this function while holding a resource the IRQ handler may need you will deadlock.

• void enable_irq(unsigned int irq)

/* kernel/irq/manage.c */

/**
 *	enable_irq - enable handling of an irq
 *	@irq: Interrupt to enable
 *
 *	Undoes the effect of one call to disable_irq().  If this
 *	matches the last disable, processing of interrupts on this
 *	IRQ line is re-enabled.
 *
 *	This function may be called from IRQ context only when
 *	desc->irq_data.chip->bus_lock and desc->chip->bus_sync_unlock are NULL !
 */
void enable_irq(unsigned int irq)
{
	unsigned long flags;
	struct irq_desc *desc = irq_get_desc_buslock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);

	if (!desc)
		return;
	if (WARN(!desc->irq_data.chip,
		 KERN_ERR "enable_irq before setup/request_irq: irq %u\n", irq))
		goto out;

	__enable_irq(desc, irq, false);
out:
	irq_put_desc_busunlock(desc, flags);
}
EXPORT_SYMBOL(enable_irq);

/* kernel/irq/manage.c */

void __enable_irq(struct irq_desc *desc, unsigned int irq, bool resume)
{
	if (resume) {
		if (!(desc->istate & IRQS_SUSPENDED)) {
			if (!desc->action)
				return;
			if (!(desc->action->flags & IRQF_FORCE_RESUME))
				return;
			/* Pretend that it got disabled ! */
			desc->depth++;
		}
		desc->istate &= ~IRQS_SUSPENDED;
	}

	printk("~~~ %s() do, irq:%d, desc->depth:%d\n", __func__, \
			irq, desc->depth);
	switch (desc->depth) {
	case 0:
 err_out:
		WARN(1, KERN_WARNING "Unbalanced enable for IRQ %d\n", irq);
		break;
	case 1: {
		if (desc->istate & IRQS_SUSPENDED)
			goto err_out;
		/* Prevent probing on this irq: */
		irq_settings_set_noprobe(desc);
		irq_enable(desc);
		check_irq_resend(desc, irq);
		/* fall-through */
	}
	default:
		desc->depth--;
	}

	printk("~~~ %s() done, irq:%d, desc->depth:%d\n", __func__, \
		irq, desc->depth);
}

/* kernel/irq/chip.c */

void irq_enable(struct irq_desc *desc)
{
	irq_state_clr_disabled(desc);
	if (desc->irq_data.chip->irq_enable)
		desc->irq_data.chip->irq_enable(&desc->irq_data);
	else
		desc->irq_data.chip->irq_unmask(&desc->irq_data);
	irq_state_clr_masked(desc);
}

disable_irq()中，desc->depth++，只有desc->depth值原来为0，++变为1的这次会去call desc->irq_data.chip->irq_disable(&desc->irq_data);

enable_irq()中，desc->depth--，只有desc->depth值原来为1，--变为0的这次会去call
desc->irq_data.chip->irq_enable(&desc->irq_data); or desc->irq_data.chip->irq_unmask(&desc->irq_data);

• void disable_irq_nosync(unsigned int irq)

/* kernel/irq/manage.c */

static int __disable_irq_nosync(unsigned int irq)
{
	unsigned long flags;
	struct irq_desc *desc = irq_get_desc_buslock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);

	if (!desc)
		return -EINVAL;
	__disable_irq(desc, irq, false);
	irq_put_desc_busunlock(desc, flags);
	return 0;
}

/**
 *	disable_irq_nosync - disable an irq without waiting
 *	@irq: Interrupt to disable
 *
 *	Disable the selected interrupt line.  Disables and Enables are
 *	nested.
 *	Unlike disable_irq(), this function does not ensure existing
 *	instances of the IRQ handler have completed before returning.
 *
 *	This function may be called from IRQ context.
 */
void disable_irq_nosync(unsigned int irq)
{
	__disable_irq_nosync(irq);
}
EXPORT_SYMBOL(disable_irq_nosync);

Unlike disable_irq(), this function does not ensure existing instances of the IRQ handler have completed before returning.
This function may be called from IRQ context.