irq自动探测机制

如果一个设备的驱动程序无法确定它说管理的设备的软件中断号irq，此时设备驱动程序可以使用irq的自动探测机制来获取其正在使用的irq。

使用自动探测机制的条件

1. 内核与驱动，必须共同努力才能完成
2. 只限于非共享中断的情况

探测前，驱动的设备关联到了某个irq，但是因为设备驱动程序还不清楚是哪个irq，因此无法调用request_irq来向该irq安装中断处理例程，所以对应irq的action为空，下面是一个设备驱动程序的使用示例：

probe_irq_on和probe_irq_off是内核为驱动程序员设计的两个自动探测的接口函数

irq自动探测的原理描述

probe_irq_on

/***	probe_irq_on	- begin an interrupt autodetect**	Commence probing for an interrupt. The interrupts are scanned*	and a mask of potential interrupt lines is returned.** 开始探测中断，扫描中断并返回潜在中断线的mask*/
unsigned long probe_irq_on(void)
{struct irq_desc *desc;unsigned long mask = 0;int i;/** quiesce the kernel, or at least the asynchronous portion*/async_synchronize_full();mutex_lock(&probing_active);/** something may have generated an irq long ago and we want to* flush such a longstanding irq before considering it as spurious.*/for_each_irq_desc_reverse(i, desc) {raw_spin_lock_irq(&desc->lock);if (!desc->action && irq_settings_can_probe(desc)) {/** Some chips need to know about probing in* progress:*/if (desc->irq_data.chip->irq_set_type)desc->irq_data.chip->irq_set_type(&desc->irq_data,IRQ_TYPE_PROBE);irq_startup(desc);}raw_spin_unlock_irq(&desc->lock);}/* Wait for longstanding interrupts to trigger. */msleep(20);/** enable any unassigned irqs* (we must startup again here because if a longstanding irq* happened in the previous stage, it may have masked itself)*/for_each_irq_desc_reverse(i, desc) {raw_spin_lock_irq(&desc->lock);if (!desc->action && irq_settings_can_probe(desc)) {desc->istate |= IRQS_AUTODETECT | IRQS_WAITING;if (irq_startup(desc))desc->istate |= IRQS_PENDING;}raw_spin_unlock_irq(&desc->lock);}/** Wait for spurious interrupts to trigger*/msleep(100);/** Now filter out any obviously spurious interrupts*/for_each_irq_desc(i, desc) {raw_spin_lock_irq(&desc->lock);if (desc->istate & IRQS_AUTODETECT) {/* It triggered already - consider it spurious. */if (!(desc->istate & IRQS_WAITING)) {desc->istate &= ~IRQS_AUTODETECT;irq_shutdown(desc);} elseif (i < 32)mask |= 1 << i;}raw_spin_unlock_irq(&desc->lock);}return mask;
}
EXPORT_SYMBOL(probe_irq_on);

probe_irq_off

/***	probe_irq_off	- end an interrupt autodetect*	@val: mask of potential interrupts (unused)**	Scans the unused interrupt lines and returns the line which*	appears to have triggered the interrupt. If no interrupt was*	found then zero is returned. If more than one interrupt is*	found then minus the first candidate is returned to indicate*	their is doubt.**	The interrupt probe logic state is returned to its previous*	value.**	BUGS: When used in a module (which arguably shouldn't happen)*	nothing prevents two IRQ probe callers from overlapping. The*	results of this are non-optimal.*/
int probe_irq_off(unsigned long val)
{int i, irq_found = 0, nr_of_irqs = 0;struct irq_desc *desc;for_each_irq_desc(i, desc) {raw_spin_lock_irq(&desc->lock);if (desc->istate & IRQS_AUTODETECT) {if (!(desc->istate & IRQS_WAITING)) {if (!nr_of_irqs)irq_found = i;nr_of_irqs++;}desc->istate &= ~IRQS_AUTODETECT;irq_shutdown(desc);}raw_spin_unlock_irq(&desc->lock);}mutex_unlock(&probing_active);if (nr_of_irqs > 1)irq_found = -irq_found;return irq_found;
}
EXPORT_SYMBOL(probe_irq_off);