linux --中断管理 -- irq的自动探测机制

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);
} else
if (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);

原文地址：https://blog.csdn.net/weixin_43604927/article/details/135939503

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