常用函数和宏定义
These symbols related to interrupt management were introduced in this chapter:
#include <linux/interrupt.h>
int request_irq(unsigned int irq, irqreturn_t (*handler)( ), unsigned long flags, const char *dev_name, void *dev_id);
void free_irq(unsigned int irq, void *dev_id);
Calls that register and unregister an interrupt handler.
dev_name为显示在/proc/interrupts中的名字
dev_id为回调中断处理程序时所给的参数，通常为本地dev结构的地址指针。
#include <linux/irq.h.h> int can_request_irq(unsigned int irq, unsigned long flags);
This function, available on the i386 and x86_64 architectures, returns a nonzero value if an attempt to allocate the given interrupt line succeeds.
#include <asm/signal.h>
SA_INTERRUPT
SA_SHIRQ
SA_SAMPLE_RANDOM
Flags for request_irq. SA_INTERRUPT requests installation of a fast handler (as opposed to a slow one). SA_SHIRQ installs a shared handler, and the third flag asserts that interrupt timestamps can be used to generate system entropy.
Modern hardware, of course, has been designed to allow the sharing of interrupts; the PCI bus requires it.
/proc/interrupts /proc/stat
Filesystem nodes that report information about hardware interrupts and installed handlers.
unsigned long probe_irq_on(void); int probe_irq_off(unsigned long);
Functions used by the driver when it has to probe to determine which interrupt line is being used by a device. The result of probe_irq_onmust be passed back to probe_irq_off after the interrupt has been generated. The return value of probe_irq_off is the detected interrupt number.
The programmer should be careful to enable interrupts on the device after the call to probe_irq_on and to disable them before callingprobe_irq_off
IRQ_NONE IRQ_HANDLED IRQ_RETVAL(int x)
The possible return values from an interrupt handler, indicating whether an actual interrupt from the device was present.
void disable_irq(int irq); //关中断且等待当前的中断处理程序完成 void disable_irq_nosync(int irq); //不等待，有风险 void enable_irq(int irq);
A driver can enable and disable interrupt reporting. If the hardware tries to generate an interrupt while interrupts are disabled, the interrupt is lost forever. A driver using a shared handler must not use these functions.
void local_irq_save(unsigned long flags); void local_irq_restore(unsigned long flags);
Use local_irq_save to disable interrupts on the local processor and remember their previous state. The flags can be passed to local_irq_restore to restore the previous interrupt state.
void local_irq_disable(void); void local_irq_enable(void);
Functions that unconditionally disable and enable interrupts on the current processor.
上下半区
规范的驱动处理一般都分上下半区，上半区为注册的中断处理函数，快速响应中断，关中断，并激活下半区。
下半区处理较耗时的任务，并允许中断，由tasklet或workqueue实现。
tasklet代码必须是原子的，而workqueue则允许睡眠。
tasklet在软中断中被执行。
DECLARE_TASKLET(name, function, data);
tasklet_schedule(&tasklet_name);
在某次tasklet被执行之前，所有schedule都是不可累积的，也就是说不管被schedule多少次，taskletk并不会被执行多次。
workqueue在专门的work process上下文中被执行。因为是process，所以可以sleep，但是不能向user space传送数据。
static struct work_struct wq; INIT_WORK(&wq, (void (*)(void *)) do_workqueue, NULL); schedule_work(&wq);