接下来，我们看看s3c2410处理器芯片的irq初始化函数
/* arch/arm/plat-s3c24xx/irq.c */
/* s3c24xx_init_irq
*
* Initialise S3C2410 IRQ system
*/
/* s3c24xx系列芯片中断初始化函数 */
void __init s3c24xx_init_irq(void)
{
unsigned long pend;
unsigned long last;
int irqno;
int i;
irqdbf("s3c2410_init_irq: clearing interrupt status flags\n");
/* first, clear all interrupts pending... */
/* 清空各个中断请求信号 */
last = 0;
for (i = 0; i < 4; i++) {
pend = __raw_readl(S3C24XX_EINTPEND);
if (pend == 0 || pend == last)
break;
__raw_writel(pend, S3C24XX_EINTPEND);
printk("irq: clearing pending ext status %08x\n", (int)pend);
last = pend;
}
last = 0;
for (i = 0; i < 4; i++) {
pend = __raw_readl(S3C2410_INTPND);
if (pend == 0 || pend == last)
break;
__raw_writel(pend, S3C2410_SRCPND);
__raw_writel(pend, S3C2410_INTPND);
printk("irq: clearing pending status %08x\n", (int)pend);
last = pend;
}
last = 0;
for (i = 0; i < 4; i++) {
pend = __raw_readl(S3C2410_SUBSRCPND);
if (pend == 0 || pend == last)
break;
printk("irq: clearing subpending status %08x\n", (int)pend);
__raw_writel(pend, S3C2410_SUBSRCPND);
last = pend;
}
/* register the main interrupts */
/* 注册主要中断 */
irqdbf("s3c2410_init_irq: registering s3c2410 interrupt handlers\n");
for (irqno = IRQ_EINT4t7; irqno <= IRQ_ADCPARENT; irqno++) {
/* set all the s3c2410 internal irqs */
switch (irqno) {
/* deal with the special IRQs (cascaded) */
case IRQ_EINT4t7:
case IRQ_EINT8t23:
case IRQ_UART0:
case IRQ_UART1:
case IRQ_UART2:
case IRQ_ADCPARENT:
set_irq_chip(irqno, &s3c_irq_level_chip); /* 设置中断操作函数集(电平) */
set_irq_handler(irqno, handle_level_irq); /* 设置中断的高层流处理函数(电平) */
break;
case IRQ_RESERVED6:
case IRQ_RESERVED24:
/* no IRQ here */
break;
default:
//irqdbf("registering irq %d (s3c irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_chip); /* 默认中断为边缘触发 */
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
}
/* setup the cascade irq handlers */
/* 设置中断的高层流处理函数 */
set_irq_chained_handler(IRQ_EINT4t7, s3c_irq_demux_extint4t7);
set_irq_chained_handler(IRQ_EINT8t23, s3c_irq_demux_extint8);
set_irq_chained_handler(IRQ_UART0, s3c_irq_demux_uart0);
set_irq_chained_handler(IRQ_UART1, s3c_irq_demux_uart1);
set_irq_chained_handler(IRQ_UART2, s3c_irq_demux_uart2);
set_irq_chained_handler(IRQ_ADCPARENT, s3c_irq_demux_adc);
/* external interrupts */
for (irqno = IRQ_EINT0; irqno <= IRQ_EINT3; irqno++) {
irqdbf("registering irq %d (ext int)\n", irqno);
set_irq_chip(irqno, &s3c_irq_eint0t4);
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
for (irqno = IRQ_EINT4; irqno <= IRQ_EINT23; irqno++) {
irqdbf("registering irq %d (extended s3c irq)\n", irqno);
set_irq_chip(irqno, &s3c_irqext_chip);
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
/* register the uart interrupts */
irqdbf("s3c2410: registering external interrupts\n");
for (irqno = IRQ_S3CUART_RX0; irqno <= IRQ_S3CUART_ERR0; irqno++) {
irqdbf("registering irq %d (s3c uart0 irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_uart0);
set_irq_handler(irqno, handle_level_irq);
set_irq_flags(irqno, IRQF_VALID);
}
for (irqno = IRQ_S3CUART_RX1; irqno <= IRQ_S3CUART_ERR1; irqno++) {
irqdbf("registering irq %d (s3c uart1 irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_uart1);
set_irq_handler(irqno, handle_level_irq);
set_irq_flags(irqno, IRQF_VALID);
}
for (irqno = IRQ_S3CUART_RX2; irqno <= IRQ_S3CUART_ERR2; irqno++) {
irqdbf("registering irq %d (s3c uart2 irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_uart2);
set_irq_handler(irqno, handle_level_irq);
set_irq_flags(irqno, IRQF_VALID);
}
for (irqno = IRQ_TC; irqno <= IRQ_ADC; irqno++) {
irqdbf("registering irq %d (s3c adc irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_adc);
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
irqdbf("s3c2410: registered interrupt handlers\n");
}
接着，我们来看一下中断处理过程 /* arch/arm/kernel/irq.c */
/*
* do_IRQ handles all hardware IRQ's. Decoded IRQs should not
* come via this function. Instead, they should provide their
* own 'handler'
*/
asmlinkage void __exception asm_do_IRQ(unsigned int irq, struct pt_regs *regs)
{
struct pt_regs *old_regs = set_irq_regs(regs); /* 保存寄存器中的内容 */
struct irq_desc *desc = irq_desc + irq; /* 获取中断源 */
/*
* Some hardware gives randomly wrong interrupts. Rather
* than crashing, do something sensible.
*/
if (irq >= NR_IRQS)
desc = &bad_irq_desc;
irq_enter();
desc_handle_irq(irq, desc); /* 调用已安装的中断高层流处理函数 */
/* AT91 specific workaround */
irq_finish(irq);
irq_exit();
set_irq_regs(old_regs);
}
接下来，我们以IRQ_UART2(s3c2410串口2中断)为例，看看中断是如何分流到我们通过request_irq注册的中断处理函数
在s3c24xx_init_irq里IRQ_S3CUART_TX2中断的中断高层流处理函数被设置为s3c_irq_demux_uart2。
s3c_irq_demux_uart2主要工作是调用s3c_irq_demux_uart对串口中断进行分流处理，因为串口中断包含Rx(接收)中断、Tx(发送）中断和Rx error(接收错误)中断
/* arch/arm/plat-s3c2410/irq.c */
static void s3c_irq_demux_uart2(unsigned int irq, struct irq_desc *desc)
{
irq = irq;
s3c_irq_demux_uart(IRQ_S3CUART_RX2);
}
s3c_irq_demux_uart通过副中断源引脚寄存器的值,判断中断源并执行相应的中断处理函数
/* arch/arm/plat-s3c2410/irq.c */
/* start: 标示发出该中断信号的是哪个uart,即其值应为
* IRQ_S3CUART_RX0、IRQ_S3CUART_RX1或IRQ_S3CUART_RX2
*/
static void s3c_irq_demux_uart(unsigned int start)
{
unsigned int subsrc, submsk;
unsigned int offset = start - IRQ_S3CUART_RX0; /* 获取该UART中断源在副中断屏蔽寄存器中的偏移量 */
struct irq_desc *desc;
/* read the current pending interrupts, and the mask
* for what it is available */
subsrc = __raw_readl(S3C2410_SUBSRCPND); /* 读取副中断源引脚寄存器 */
submsk = __raw_readl(S3C2410_INTSUBMSK); /* 读取副中断屏蔽寄存器 */
irqdbf2("s3c_irq_demux_uart: start=%d (%d), subsrc=0x%08x,0x%08x\n",
start, offset, subsrc, submsk);
subsrc &= ~submsk; /* 只留下已使能(未屏蔽)的中断源 */
subsrc >>= offset; /* 截取发送中断的uart源到subsrc低3位 */
subsrc &= 7;
if (subsrc != 0)
{
desc = irq_desc + start;
if (subsrc & 1) /* Rx中断 */
desc_handle_irq(start, desc);
desc++;
if (subsrc & 2) /* Tx中断 */
desc_handle_irq(start+1, desc);
desc++;
if (subsrc & 4) /* Rx error中断 */
desc_handle_irq(start+2, desc);
}
}
desc_handle_irq实际上只是调用了desc->handle_irq来执行已安装的中断高层流处理函数。假设这里串口2发起的中断为Tx中断，即IRQ_S3CUART_TX2。IRQ_S3CUART_TX2的中断高层流处理函数已在s3c24xx_init_irq里通过set_irq_handler设置为handle_level_irq。
/* include/asm-arm/mach/irq.h */
/*
* Obsolete inline function for calling irq descriptor handlers.
*/
static inline void desc_handle_irq(unsigned int irq, struct irq_desc *desc)
{
desc->handle_irq(irq, desc);
}
handle_level_irq主要工作是获取该中断的action链表(所有安装在该中断号上的中断处理函数其实就是一个action结构体，详见request_irq的实现)，然后传递给handle_IRQ_event。
/* kernel/irq/chip.c */
/*
* handle_level_irq - Level type irq handler
* @irq: the interrupt number
* @desc: the interrupt description structure for this irq
*
* Level type interrupts are active as long as the hardware line has
* the active level. This may require to mask the interrupt and unmask
* it after the associated handler has acknowledged the device, so the
* interrupt line is back to inactive.
*/
void fastcall handle_level_irq(unsigned int irq, struct irq_desc *desc)
{
unsigned int cpu = smp_processor_id();
struct irqaction *action;
irqreturn_t action_ret;
spin_lock(&desc->lock);
mask_ack_irq(desc, irq);
if (unlikely(desc->status & IRQ_INPROGRESS))
goto out_unlock;
desc->status &= ~(IRQ_REPLAY | IRQ_WAITING);
kstat_cpu(cpu).irqs[irq]++;
/*
* If its disabled or no action available
* keep it masked and get out of here
*/
/* 获取该中断的action链表 */
action = desc->action;
if (unlikely(!action || (desc->status & IRQ_DISABLED)))
goto out_unlock;
desc->status |= IRQ_INPROGRESS;
spin_unlock(&desc->lock);
/* 调用handle_IRQ_event，执行已安装在该中断号上的所有中断函数 */
action_ret = handle_IRQ_event(irq, action);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
spin_lock(&desc->lock);
desc->status &= ~IRQ_INPROGRESS;
if (!(desc->status & IRQ_DISABLED) && desc->chip->unmask)
desc->chip->unmask(irq);
out_unlock:
spin_unlock(&desc->lock);
}
handle_IRQ_event主要作用就是执行那些已安装的中断处理函数action->handler /* kernel/irq/handle.c */
/*
* handle_IRQ_event - irq action chain handler
* @irq: the interrupt number
* @action: the interrupt action chain for this irq
*
* Handles the action chain of an irq event
*/
irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
{
irqreturn_t ret, retval = IRQ_NONE;
unsigned int status = 0;
handle_dynamic_tick(action);
if (!(action->flags & IRQF_DISABLED))
local_irq_enable_in_hardirq();
/* 循环调用安装在该中断号irq上的中断处理函数 */
do
{
/* action->handler就是我们调用request_irq时，
* 安装的中断处理函数 */
ret = action->handler(irq, action->dev_id);
if (ret == IRQ_HANDLED)
status |= action->flags;
retval |= ret;
action = action->next;
} while (action);
if (status & IRQF_SAMPLE_RANDOM)
add_interrupt_randomness(irq);
local_irq_disable();
return retval;
}
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