二 註冊中斷
這部分我們以3sc2410下的watchdog的中斷爲例來講解中斷的註冊及調用過程。
drivers/char/watchdog/s3c2410_wdt.c:
static int s3c2410wdt_probe(struct platform_device *pdev)
{
……
/*註冊中斷*/
ret = request_irq(res->start, s3c2410wdt_irq, 0, pdev->name, pdev);
……
}
在s3c2410wdt_probe函數中爲watchdog註冊了一箇中斷，中斷號爲IRQ_WDT，
#define IRQ_WDT S3C2410_IRQ(9)
中斷處理函數是s3c2410wdt_irq。
我們來看request_irq是如何實現的：
kernel/irq/Manage.c:
/**
* request_irq - allocate an interrupt line
* @irq: Interrupt line to allocate
* @handler: Function to be called when the IRQ occurs
* @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.
*
* 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_DISABLED Disable local interrupts while processing
* IRQF_SAMPLE_RANDOM The interrupt can be used for entropy
*
*/
int request_irq(unsigned int irq,
irqreturn_t (*handler)(int, void *, struct pt_regs *),
unsigned long irqflags, const char *devname, void *dev_id)
{
struct irqaction *action;
int retval;
#ifdef CONFIG_LOCKDEP
/*
* Lockdep wants atomic interrupt handlers:
*/
irqflags |= SA_INTERRUPT;
#endif
/*
* 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).
*/
/*允許共享的中斷必須要有一個獨一無二的dev_id, 看上面函數的解釋
if ((irqflags & IRQF_SHARED) && !dev_id)
return -EINVAL;
if (irq >= NR_IRQS) /*中斷號是否合法*/
return -EINVAL;
/*這個標記對s3c2410來說在s3c24xx_init_irq裏通過調用set_irq_flags()被去掉了*/
if (irq_desc[irq].status & IRQ_NOREQUEST)
return -EINVAL;
if (!handler) /*中斷例程*/
return -EINVAL;
/*分配一個irqaction對象，來保存這個中斷信息*/
action = kmalloc(sizeof(struct irqaction), GFP_ATOMIC);
if (!action)
return -ENOMEM;
/*保存中斷例程等信息*/
action->handler = handler;
action->flags = irqflags;
cpus_clear(action->mask); /*清除相應位*/
action->name = devname;
action->next = NULL;
action->dev_id = dev_id;
select_smp_affinity(irq);
retval = setup_irq(irq, action);/*申請中斷*/
if (retval)
kfree(action);
return retval;
}
該函數的功能及參數含義在函數頭有詳細的說明，這裏就不多介紹了，值得注意的是我們在申請中斷之前，必須要去掉該中斷的IRQ_NOREQUEST標記(系統初始化的時候賦了這個標記)， 具體方法是調用set_irq_flags()函數。
接着看setup_irq
kernel/irq/Manage.c:
/*
* Internal function to register an irqaction - typically used to
* allocate special interrupts that are part of the architecture.
*/
int setup_irq(unsigned int irq, struct irqaction *new)
{
struct irq_desc *desc = irq_desc + irq; /*獲取保存該中斷的中斷描述符地址*/
struct irqaction *old, **p;
unsigned long flags;
int shared = 0;
if (irq >= NR_IRQS)
return -EINVAL;
/*對於s3c2410的中斷在s3c24xx_init_irq裏已經初始化過了*/
if (desc->chip == &no_irq_chip)
return -ENOSYS;
/*
* Some drivers like serial.c use request_irq() heavily,
* so we have to be careful not to interfere with a
* running system.
*/
if (new->flags & IRQF_SAMPLE_RANDOM) {
/*
* This function might sleep, we want to call it first,
* outside of the atomic block.
* Yes, this might clear the entropy pool if the wrong
* driver is attempted to be loaded, without actually
* installing a new handler, but is this really a problem,
* only the sysadmin is able to do this.
*/
rand_initialize_irq(irq);
}
/*
* The following block of code has to be executed atomically
*/
/*
* 下面if代碼段主要是查看該中斷是否可以共享，如可以，則把中斷例程鏈入中斷例程
* list中, 至於中斷共享的條件有： 1 觸發方式相同， 2 都允許中斷共享*/
spin_lock_irqsave(&desc->lock, flags);
p = &desc->action;
old = *p;
if (old) { /*對於IRQ_WDT，這個if不成立，但它已經設置了handle_irq 喔*/
/*
* 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.
*/
/*判斷能否共享中斷*/
if (!((old->flags & new->flags) & IRQF_SHARED) ||
((old->flags ^ new->flags) & IRQF_TRIGGER_MASK))
goto mismatch;
#if defined(CONFIG_IRQ_PER_CPU)
/* All handlers must agree on per-cpuness */
if ((old->flags & IRQF_PERCPU) !=
(new->flags & IRQF_PERCPU))
goto mismatch;
#endif
/* add new interrupt at end of irq queue */
/*把中斷例程加入list中*/
do {
p = &old->next;
old = *p;
} while (old);
shared = 1;
}
*p = new; /*該行很關鍵， 它把中斷的處理函數添加到該中斷描述符的中斷例程list裏*/
#if defined(CONFIG_IRQ_PER_CPU)
if (new->flags & IRQF_PERCPU)
desc->status |= IRQ_PER_CPU;
#endif
if (!shared) {
/*對於IRQ_WDT來說這步是多餘的，初始化的時候已做過*/
irq_chip_set_defaults(desc->chip);
/* Setup the type (level, edge polarity) if configured: */
/*對於IRQ_WDT來說，沒有定義觸發方式， 即默認觸發方式*/
if (new->flags & IRQF_TRIGGER_MASK) {
/*如果要設觸發方式，則調用平臺特定的函數，因此如果我們的平臺要實現該功能則必*須要在irq_chip對象里加入對set_type 函數的支持*/
if (desc->chip && desc->chip->set_type)
desc->chip->set_type(irq,
new->flags & IRQF_TRIGGER_MASK);
else
/*
* IRQF_TRIGGER_* but the PIC does not support
* multiple flow-types?
*/
printk(KERN_WARNING "No IRQF_TRIGGER set_type "
"function for IRQ %d (%s)/n", irq,
desc->chip ? desc->chip->name :
"unknown");
} else
/*這函數只是簡單的檢查是否有handle_irq*/
compat_irq_chip_set_default_handler(desc);
/*去掉中斷的相關狀態，讓它就緒*/
desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |
IRQ_INPROGRESS);
if (!(desc->status & IRQ_NOAUTOEN)) {
/*使能該中斷*/
desc->depth = 0;
desc->status &= ~IRQ_DISABLED;
if (desc->chip->startup)
desc->chip->startup(irq); /*平臺相關函數*/
else
desc->chip->enable(irq); /*平臺相關函數*/
} else
/* Undo nested disables: */
desc->depth = 1;
}
spin_unlock_irqrestore(&desc->lock, flags);
new->irq = irq;
register_irq_proc(irq); /*在/proc/irq/下創建該中斷的一個文件*/
new->dir = NULL;
register_handler_proc(irq, new); /*爲/proc/irq/下創建的文件設置處理函數*/
return 0;
mismatch:
spin_unlock_irqrestore(&desc->lock, flags);
if (!(new->flags & IRQF_PROBE_SHARED)) {
printk(KERN_ERR "IRQ handler type mismatch for IRQ %d/n", irq);
dump_stack();
}
return -EBUSY;
}
該函數主要是安裝了一箇中斷，並使能它。 我們先看使能函數，它是平臺相關的，對於s3c2410的IRQ_WDT來說使用的是默認的使能函數(default_startup(),初始化賦值)，如果我們要使用自己的使能函數，只要在chip對象裏添加就行了。
kernel/irq/Chip.c:
static unsigned int default_startup(unsigned int irq)
{
irq_desc[irq].chip->enable(irq);
return 0;
}
對於IRQ_WDT來說調用的irq_desc[irq].chip->enable(irq)仍是默認函數：default_enable（）
kernel/irq/Chip.c:
static void default_enable(unsigned int irq)
{
struct irq_desc *desc = irq_desc + irq;
desc->chip->unmask(irq); /*unmask該中斷*/
desc->status &= ~IRQ_MASKED;
}
呵呵，對於IRQ_WDT來說這次的調用desc->chip->unmask(irq)，實際上是s3c_irq_unmask, 具體可查看前面分析的chip對象。
arch/arm/mach-s3c2410/Irq.c:
static void
s3c_irq_unmask(unsigned int irqno)
{
unsigned long mask;
if (irqno != IRQ_TIMER4 && irqno != IRQ_EINT8t23)
irqdbf2("s3c_irq_unmask %d/n", irqno);
irqno -= IRQ_EINT0;
mask = __raw_readl(S3C2410_INTMSK);
mask &= ~(1UL << irqno);
__raw_writel(mask, S3C2410_INTMSK);
}
對着s3c2410的data sheet一看就知道了， 就是打開相應中斷。
至此中斷處理函數安裝好了，中斷也打開了，系統就可以正確的響應中斷了。
Ok，到此爲止IRQ_WDT的中斷註冊過程已完成，此時的中斷描述符如下所示：
