作者:独孤九贱;
版权所有,转载请注明出处。
一、概述
中断,本质上是一个电信号,早期的计算的并没有中断这一概念,这使得CPU与外围设备的交互变得困难,CPU需要不断的轮询,以探测外围设备是否有数据需要处理。这浪费大量的资源。中断的出现,将CPU从这一任务中解放出来,CPU与外设的处理,变为异步,它可以喝着茶,听着音乐,然后等待外设的报告。
Linux中的中断,除了包含外围设备引发的硬中断外,还有更多宽泛的概念,如CPU引发的同步中断或异常、软中断等。不过本文如未特别注明,都是描述外围设备发出的异步中断。
事实上,外围设备并不能直接发中断给CPU。是的,老大随时来看我轮询一下,浪费他的时间与精力,我也不能想找老大就找老大,得找他的小蜜,外设借助一个称为“中断控制器”的中间组件来完成请求。这个过程叫IRQ(中断请求),中断控制器在处理完相应的电工任务后,将中断请求转发到CPU的中断输入。例如,下图展示了一个典型的x86平台的8259A中断控制器:
二、中断控制器
为了屏蔽各种硬件平台的区别,Linux提供了一个统一抽像的平台来实现中断子系统。irq_chip结构用于描述一个硬件中断控制器,它封装了控制器的名称(如XTPIC或IO-APIC)和控制器相应的操作:
-
struct irq_chip {
-
const char *name; //控制器名称
-
unsigned int (*startup)(unsigned int irq); //第一次激活时调用,用于第一次初始化IRQ
-
void (*shutdown)(unsigned int irq); //对应的关闭操作
-
void (*enable)(unsigned int irq); //激活IRQ
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void (*disable)(unsigned int irq); //禁用IRQ
-
-
void (*ack)(unsigned int irq); //显示的中断确认操作
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void (*mask)(unsigned int irq); //屏蔽中断
-
void (*mask_ack)(unsigned int irq); //屏幕并确认
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void (*unmask)(unsigned int irq); //屏蔽的反向操作
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void (*eoi)(unsigned int irq); //end of interrupt,提供处理中断时一个到硬件的回调
-
-
void (*end)(unsigned int irq); //end操作表示中断处理在电流层结束
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int (*set_affinity)(unsigned int irq, //设置中断亲和
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const struct cpumask *dest);
-
int (*retrigger)(unsigned int irq);
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int (*set_type)(unsigned int irq, unsigned int flow_type); //设IRQ电流类型
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int (*set_wake)(unsigned int irq, unsigned int on); //设置唤醒???
-
-
/* Currently used only by UML, might disappear one day.*/
-
#ifdef CONFIG_IRQ_RELEASE_METHOD
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void (*release)(unsigned int irq, void *dev_id);
-
#endif
-
/*
-
* For compatibility, ->typename is copied into ->name.
-
* Will disappear.
-
*/
-
const char *typename;
-
};
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大多数的操作可以根据名称了解一二。该结构考虑到了各种不同的体系结构,所以一个特系结构的使用,通常仅是它的一个子集,甚至是很小的一个子系,仍然以8259A为例:
-
struct irq_chip i8259A_chip = {
-
.name = "XT-PIC",
-
.mask = disable_8259A_irq,
-
.disable = disable_8259A_irq,
-
.unmask = enable_8259A_irq,
-
.mask_ack = mask_and_ack_8259A,
-
};
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三、中断描述符
每个中断都有一个编号,系统可以根据编号很容易地区分来访者,是鼠标,还是键盘,或者是网卡。只是很可惜,出于很多原因(例如短视或成本考虑),在很多体系结构上,提供的编号是很少的,例如图1中显示的,两个8259A芯片,总共提供了16个中断槽位。虽然曾经看来,对于个人计算机这已经足够了,只是时过境迁,又到了改变的时候,例如,多个外设共享一个中断,称之为中断共享,有过PCI驱动编写经验的都接触过,当然,这需要硬件和内核同时支持。
在IA-32 CPU上,为外围设备都供了16个中断号,从32-47,不过如果看一下/proc/interrupts就会发现,外围设备的IRQ编号是从0开始到15的,这意味着,中断控制器的一个重要任务,就是对IRQ编号和中断号进行映射,在IA-32上,这个映射,就需要加上32即可。
每个中断号的信息使用IRQ描述符struct irq_desc表示:
-
struct irq_desc {
-
unsigned int irq;
-
……
-
irq_flow_handler_t handle_irq; //指向上述控制芯片的电流处理程序
-
struct irq_chip *chip; //指向上述的控制芯片
-
……
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struct irqaction *action; /* IRQ action list */ //指向IRQ的中断action列表
-
……
-
} ____cacheline_internodealigned_in_smp;
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IRQ相关信息的管理的关键之处在于,内核引入一个irq_desc 类型的全局数组来记录之,每个数组的项对应一个IRQ编号,数组槽位与中断号一一对应,IRQ0在位置0,诸如此类。
数组irq_desc_ptrs的初始化在kernel/irq/handle.c
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struct irq_desc **irq_desc_ptrs __read_mostly;
-
-
irq_desc_legacy是一个用于初始化的临时中介:
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static struct irq_desc irq_desc_legacy[NR_IRQS_LEGACY] __cacheline_aligned_in_smp = {
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[0 ... NR_IRQS_LEGACY-1] = {
-
.irq = -1,
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.status = IRQ_DISABLED,
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.chip = &no_irq_chip,
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.handle_irq = handle_bad_irq,
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.depth = 1,
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.lock = __SPIN_LOCK_UNLOCKED(irq_desc_init.lock),
-
}
-
};
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这里使用了一个gcc扩展,将所有成员irq号都初始化为-1,其handle_irq都指向handle_bad_irq。
irq_to_desc函数可以根据设备中断号取得相应的中断描述符:
-
struct irq_desc *irq_to_desc(unsigned int irq)
-
{
-
if (irq_desc_ptrs && irq < nr_irqs)
-
return irq_desc_ptrs[irq];
-
-
return NULL;
-
}
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中断描述符中,其最后一个成员action指向中断处理程序。这将在后文描述,先来看中断描述符的初始化,这在early_irq_init函数中完成:
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int __init early_irq_init(void)
-
{
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struct irq_desc *desc;
-
-
desc = irq_desc_legacy;
-
-
//为中断描述符分配槽位
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irq_desc_ptrs = kcalloc(nr_irqs, sizeof(void *), GFP_NOWAIT);
-
-
legacy_count = ARRAY_SIZE(irq_desc_legacy);
-
-
//初始化之
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for (i = 0; i < legacy_count; i++) {
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desc[i].irq = i;
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desc[i].kstat_irqs = kstat_irqs_legacy + i * nr_cpu_ids;
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lockdep_set_class(&desc[i].lock, &irq_desc_lock_class);
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alloc_desc_masks(&desc[i], node, true);
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init_desc_masks(&desc[i]);
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irq_desc_ptrs[i] = desc + i;
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}
-
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//初始化余下的
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for (i = legacy_count; i < nr_irqs; i++)
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irq_desc_ptrs[i] = NULL;
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}
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这样,每个irq_desc_ptrs的槽位的初始化工作就完成了。值得注意的是,这里并没有初始化中断描述符的电流处理句柄handle_irq成员。这是留到具体的控制器中去完成的,还是以8259A为例:
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void make_8259A_irq(unsigned int irq)
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{
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disable_irq_nosync(irq);
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io_apic_irqs &= ~(1<<irq);
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set_irq_chip_and_handler_name(irq, &i8259A_chip, handle_level_irq,
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"XT");
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enable_irq(irq);
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}
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set_irq_chip_and_handler_name函数是内核提供的处理注册irq_chip和设置电流处理程序的API之一:
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void
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set_irq_chip_and_handler_name(unsigned int irq, struct irq_chip *chip,
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irq_flow_handler_t handle, const char *name)
-
{
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//取得IRQ对应的中断描述符,设置其chip成员
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set_irq_chip(irq, chip);
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//设置IRQ对应的中断描述符的handle_irq成员
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__set_irq_handler(irq, handle, 0, name);
-
}
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这样,i8259A_chip控制器的电流处理程序被注册为handle_level_irq,即为电平触发中断,对应的,边沿触发中断的处理程序是handle_edge_irq。
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void
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handle_level_irq(unsigned int irq, struct irq_desc *desc)
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{
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struct irqaction *action;
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irqreturn_t action_ret;
-
-
spin_lock(&desc->lock);
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mask_ack_irq(desc, irq);
-
-
//后面的代码在应答的中断后,会调置IRQ_INPROGRESS标志,这里做一个简单检查
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if (unlikely(desc->status & IRQ_INPROGRESS))
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goto out_unlock;
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//清除IRQ_REPLAY | IRQ_WAITING标志位
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desc->status &= ~(IRQ_REPLAY | IRQ_WAITING);
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//统计
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kstat_incr_irqs_this_cpu(irq, desc);
-
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/*
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* If its disabled or no action available
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* keep it masked and get out of here
-
*/
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//从中断描述符中取得action
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action = desc->action;
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//如果没有action,或者是中断被关闭,退出
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if (unlikely(!action || (desc->status & IRQ_DISABLED)))
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goto out_unlock;
-
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//设置IRQ_INPROGRESS,表示正在处理
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desc->status |= IRQ_INPROGRESS;
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spin_unlock(&desc->lock);
-
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//调用高层的中断处理程序handle_IRQ_event进一步处理
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action_ret = handle_IRQ_event(irq, action);
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if (!noirqdebug)
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note_interrupt(irq, desc, action_ret);
-
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spin_lock(&desc->lock);
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//处理完毕,清除正在处理标志
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desc->status &= ~IRQ_INPROGRESS;
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//如果IRQ没有被禁用,调用chip的unmask
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if (!(desc->status & IRQ_DISABLED) && desc->chip->unmask)
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desc->chip->unmask(irq);
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out_unlock:
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spin_unlock(&desc->lock);
-
}
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略过一些硬件的细节差异,handle_edge_irq处理过程类似,它最终也会调用高层的中断处理程序handle_IRQ_event。
四、中断处理程序函数
每个中断处理程序函数都由结构struct irqaction表示,也就是上述中断描述符的最后一个成员:
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struct irqaction {
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irq_handler_t handler;
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unsigned long flags;
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cpumask_t mask;
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const char *name;
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void *dev_id;
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struct irqaction *next;
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int irq;
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struct proc_dir_entry *dir;
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irq_handler_t thread_fn;
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struct task_struct *thread;
-
unsigned long thread_flags;
-
};
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该结构中,最重要的叫员就是处理函数本身,也就是其第一个成员。
flags包含一些标志信,例如IRQF_SHARED/IRQF_TIMER等。
mask存储其CPU位图掩码;
name和dev_id唯一地标识一个中断处理程序;
next成员用于实现共享的IRQ处理程序,相同irq号的一个或几个irqaction汇聚在一个链表中。
小结一下,上述三个重要数据结构的关系就很清楚了:
irq_desc数组包含若干成员,每个成员都一个chip指针,指向对应的中断控制器结构,action指向,指向中断处理函数结构irqaction,若干个具体相同irq的中断处理函数结构串在一个链表上。
irqaction是中断子系统面向驱动程序界面提供的接口,驱动程序在初始化的时候向内核注册,调用request_irq向中断子系统注册,request_irq函数会构造一个action,并将其关联到相应的中断描述符上。
五、IDT表与中断的触发
中断的触发,或者称之为中断路由,表示一个中断如何达到上述的中断处理函数中。
IDT(Interrupt Descriptor Table)中断描述表,IDT是个有256个入口的线形表,每个中断向量关联了一个中断处理过程。当计算机运行在实模式时,IDT被初始化并由BIOS使用。然而,一旦真正进入了Linux内核,IDT就被移到内存的另一个区域,并进行进入实模式的初步初始化。内核的初始化流程如下:
-
start_kernel
-
->init_IRQ
-
->native_init_IRQ
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-
void __init native_init_IRQ(void)
-
{
-
……
-
//更新外部中断(IRQ)的IDT表项
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for (i = FIRST_EXTERNAL_VECTOR; i < NR_VECTORS; i++) {
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/* IA32_SYSCALL_VECTOR could be used in trap_init already. */
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//跳过系统调用(trap)使用过的槽位
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if (!test_bit(i, used_vectors))
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set_intr_gate(i, interrupt[i-FIRST_EXTERNAL_VECTOR]);
-
}
-
}
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set_intr_gate在IDT的第i个表项插入一个中断门。门中的段选择符设置为内核代码的段选择符,基偏移量为中断处理程序的地址,
即为第二个参数interrupt[i-FIRST_EXTERNAL_VECTOR]。
interrupt数组在entry_32.S中定义,它本质上都会跳转到common_interrupt:
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.section .init.rodata,"a"
-
ENTRY(interrupt)
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.text
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.p2align 5
-
.p2align CONFIG_X86_L1_CACHE_SHIFT
-
ENTRY(irq_entries_start)
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RING0_INT_FRAME
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vector=FIRST_EXTERNAL_VECTOR
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.rept (NR_VECTORS-FIRST_EXTERNAL_VECTOR+6)/7
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.balign 32
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.rept 7
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.if vector < NR_VECTORS
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.if vector <> FIRST_EXTERNAL_VECTOR
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CFI_ADJUST_CFA_OFFSET -4
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.endif
-
1: pushl $(~vector+0x80) /* Note: always in signed byte range */
-
CFI_ADJUST_CFA_OFFSET 4
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.if ((vector-FIRST_EXTERNAL_VECTOR)%7) <> 6
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jmp 2f
-
.endif
-
.previous
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.long 1b
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.text
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vector=vector+1
-
.endif
-
.endr
-
2: jmp common_interrupt
-
.endr
-
END(irq_entries_start)
-
-
.previous
-
END(interrupt)
-
.previous
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common_interrupt是所有外部中断的统一入口:
-
/*
-
* the CPU automatically disables interrupts when executing an IRQ vector,
-
* so IRQ-flags tracing has to follow that:
-
*/
-
.p2align CONFIG_X86_L1_CACHE_SHIFT
-
common_interrupt:
-
//将中断向量号减256。内核用负数表示所有的中断
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addl $-0x80,(%esp) /* Adjust vector into the [-256,-1] range */
-
//调用SAVE_ALL宏保存寄存器的值
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SAVE_ALL
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TRACE_IRQS_OFF
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//保存栈顶地址
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movl %esp,%eax
-
//调用do_IRQ函数
-
call do_IRQ
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//从中断返回
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jmp ret_from_intr
-
ENDPROC(common_interrupt)
-
CFI_ENDPROC
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这样,就进入了著名的do_IRQ函数了,到这里,基本上有平台相关的汇编代码的处理流程就结束了,相对而言,我还是更喜欢C语言:
-
/*
-
* do_IRQ handles all normal device IRQ's (the special
-
* SMP cross-CPU interrupts have their own specific
-
* handlers).
-
*/
-
unsigned int __irq_entry do_IRQ(struct pt_regs *regs)
-
{
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//取得原来的寄存器
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struct pt_regs *old_regs = set_irq_regs(regs);
-
-
/* high bit used in ret_from_ code */
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//取得中断向量号
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unsigned vector = ~regs->orig_ax;
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unsigned irq;
-
-
//退出idle进程
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exit_idle();
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//进入中断
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irq_enter();
-
-
//中断线号与设备的中断号之间对应关系,由系统分派,分派表是一个per-cpu变量vector_irq
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irq = __get_cpu_var(vector_irq)[vector];
-
-
//处理之
-
if (!handle_irq(irq, regs)) {
-
//应答APIC
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ack_APIC_irq();
-
-
if (printk_ratelimit())
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pr_emerg("%s: %d.%d No irq handler for vector (irq %d)\n",
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__func__, smp_processor_id(), vector, irq);
-
}
-
-
//结束中断
-
irq_exit();
-
-
set_irq_regs(old_regs);
-
return 1;
-
}
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handle_irq函数根据中断号,查找相应的desc结构,调用其handle_irq:
-
bool handle_irq(unsigned irq, struct pt_regs *regs)
-
{
-
struct irq_desc *desc;
-
int overflow;
-
-
overflow = check_stack_overflow();
-
-
desc = irq_to_desc(irq); //取得irq对应的中断描述符,irq_to_desc函数一开始就已经分析过了
-
if (unlikely(!desc))
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return false;
-
-
if (!execute_on_irq_stack(overflow, desc, irq)) {
-
if (unlikely(overflow))
-
print_stack_overflow();
-
desc->handle_irq(irq, desc);
-
}
-
-
return true;
-
}
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如果是在中断栈上调用,则稍微复杂一点,需要先构造一个中断栈,再调用handle_irq。
-
static inline int
-
execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq)
-
{
-
union irq_ctx *curctx, *irqctx;
-
u32 *isp, arg1, arg2;
-
-
curctx = (union irq_ctx *) current_thread_info();
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irqctx = __get_cpu_var(hardirq_ctx);
-
-
/*
-
* this is where we switch to the IRQ stack. However, if we are
-
* already using the IRQ stack (because we interrupted a hardirq
-
* handler) we can't do that and just have to keep using the
-
* current stack (which is the irq stack already after all)
-
*/
-
if (unlikely(curctx == irqctx))
-
return 0;
-
-
/* build the stack frame on the IRQ stack */
-
isp = (u32 *) ((char *)irqctx + sizeof(*irqctx));
-
irqctx->tinfo.task = curctx->tinfo.task;
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irqctx->tinfo.previous_esp = current_stack_pointer;
-
-
/*
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* Copy the softirq bits in preempt_count so that the
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* softirq checks work in the hardirq context.
-
*/
-
irqctx->tinfo.preempt_count =
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(irqctx->tinfo.preempt_count & ~SOFTIRQ_MASK) |
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(curctx->tinfo.preempt_count & SOFTIRQ_MASK);
-
-
if (unlikely(overflow))
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call_on_stack(print_stack_overflow, isp);
-
-
asm volatile("xchgl %%ebx,%%esp \n"
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"call *%%edi \n"
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"movl %%ebx,%%esp \n"
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: "=a" (arg1), "=d" (arg2), "=b" (isp)
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: "0" (irq), "1" (desc), "2" (isp),
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"D" (desc->handle_irq)
-
: "memory", "cc", "ecx");
-
return 1;
-
}
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中断栈的构造过程,我在《Linux软中断的实现》一文中分析过了,可以在坛子中搜索。
如前所述,handle_irq函数指针,指向了handle_level_irq,或者是handle_edge_irq。不论是哪一种,中断电流处理函数在会调用handle_IRQ_event进一步处理,handle_IRQ_event函数的本质是遍历中断号上所有的action,调用其handler。这是在设备驱动初始化时向中断子系统注册的:
/**
* 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;
//因为CPU会禁止中断,这里将其打开,如果没有指定IRQF_DISABLED标志的话,它表示处理程序在中断禁止情况下运行
if (!(action->flags & IRQF_DISABLED))
local_irq_enable_in_hardirq();
//遍历当前irq的action链表中的所有action,调用之
do {
//打开中断跟踪
trace_irq_handler_entry(irq, action);
//调用中断处理函数
ret = action->handler(irq, action->dev_id);
//结束跟踪
trace_irq_handler_exit(irq, action, ret);
switch (ret) {
case IRQ_WAKE_THREAD:
/*
* Set result to handled so the spurious check
* does not trigger.
*/
ret = IRQ_HANDLED;
/*
* Catch drivers which return WAKE_THREAD but
* did not set up a thread function
*/
if (unlikely(!action->thread_fn)) {
warn_no_thread(irq, action);
break;
}
/*
* Wake up the handler thread for this
* action. In case the thread crashed and was
* killed we just pretend that we handled the
* interrupt. The hardirq handler above has
* disabled the device interrupt, so no irq
* storm is lurking.
*/
if (likely(!test_bit(IRQTF_DIED,
&action->thread_flags))) {
set_bit(IRQTF_RUNTHREAD, &action->thread_flags);
wake_up_process(action->thread);
}
/* Fall through to add to randomness */
case IRQ_HANDLED:
status |= action->flags;
break;
default:
break;
}
retval |= ret;
//取得链表中的下一个action,如果有的话
action = action->next;
} while (action);
//如果指定了标志,则使用中断间隔时间为随机数产生器产生熵
if (status & IRQF_SAMPLE_RANDOM)
add_interrupt_randomness(irq);
//关闭中断,do_IRQ进入下一轮循环——等待新的中断到来
local_irq_disable();
return retval;
}
六、中断处理函数的注册 request_irq
很显然,如果驱动程序需要处理与中断相关的工作,它就应该注册一个中断处理程序。也就是构造一个前文所述irqaction,
并挂到前文描述中,中断描述符的链表中去,request_irq API函数完成这一工作,其原型如下:
@irq:要分配的中断号
@hander: 中断处理函数指针,这是工作的核心
@flags:中断标志位,可以是IRQF_DISABLED,IRQF_SAMPLE_RANDOM,IRQF_TIMER,IRQF_SHARED等;
@name:中断设备的文件描述;
@dev:用于中断共享,它提供设备的唯一标识信息。
-
static inline int __must_check
-
request_irq(unsigned int irq, irq_handler_t handler, unsigned long flags,
-
const char *name, void *dev)
-
{
-
return request_threaded_irq(irq, handler, NULL, flags, name, dev);
-
}
复制代码
例如,e100驱动中注册其中断处理函数:
-
static int e100_up(struct nic *nic)
-
{
-
……
-
if ((err = request_irq(nic->pdev->irq, e100_intr, IRQF_SHARED,
-
nic->netdev->name, nic->netdev)))
-
……
-
}
复制代码
与老的request_irq不同在于,request_irq调用了request_threaded_irq,而不再是setup_irq函数。
这一改变的的理由在于,前者允许传递一个线程处理函数thread_fn,不过request_irq使用传递为NULL:
-
-
int request_threaded_irq(unsigned int irq, irq_handler_t handler,
-
irq_handler_t thread_fn, unsigned long irqflags,
-
const char *devname, void *dev_id)
-
{
-
struct irqaction *action;
-
struct irq_desc *desc;
-
int retval;
-
-
/*
-
* handle_IRQ_event() always ignores IRQF_DISABLED except for
-
* the _first_ irqaction (sigh). That can cause oopsing, but
-
* the behavior is classified as "will not fix" so we need to
-
* start nudging drivers away from using that idiom.
-
*/
-
//标志位检查
-
if ((irqflags & (IRQF_SHARED|IRQF_DISABLED)) ==
-
(IRQF_SHARED|IRQF_DISABLED)) {
-
pr_warning(
-
"IRQ %d/%s: IRQF_DISABLED is not guaranteed on shared IRQs\n",
-
irq, devname);
-
}
-
-
#ifdef CONFIG_LOCKDEP
-
/*
-
* Lockdep wants atomic interrupt handlers:
-
*/
-
irqflags |= IRQF_DISABLED;
-
#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).
-
*/
-
//共享中断,需要指定设备ID
-
if ((irqflags & IRQF_SHARED) && !dev_id)
-
return -EINVAL;
-
-
//获取对应的中断描述符
-
desc = irq_to_desc(irq);
-
if (!desc)
-
return -EINVAL;
-
-
//IRQ_NOREQUEST标志意味着中断不能被请求注册
-
if (desc->status & IRQ_NOREQUEST)
-
return -EINVAL;
-
if (!handler)
-
return -EINVAL;
-
-
//分配一个irqaction
-
action = kzalloc(sizeof(struct irqaction), GFP_KERNEL);
-
if (!action)
-
return -ENOMEM;
-
-
//初始化之
-
action->handler = handler;
-
action->thread_fn = thread_fn;
-
action->flags = irqflags;
-
action->name = devname;
-
action->dev_id = dev_id;
-
-
//注册IRQ
-
retval = __setup_irq(irq, desc, action);
-
if (retval)
-
kfree(action);
-
-
//调试操作
-
#ifdef CONFIG_DEBUG_SHIRQ
-
if (irqflags & IRQF_SHARED) {
-
/*
-
* It's a shared IRQ -- the driver ought to be prepared for it
-
* to happen immediately, so let's make sure....
-
* We disable the irq to make sure that a 'real' IRQ doesn't
-
* run in parallel with our fake.
-
*/
-
unsigned long flags;
-
-
disable_irq(irq);
-
local_irq_save(flags);
-
-
handler(irq, dev_id);
-
-
local_irq_restore(flags);
-
enable_irq(irq);
-
}
-
#endif
-
return retval;
-
}
复制代码
具体的注册工作落实到了__setup_irq函数:
-
/*
-
* Internal function to register an irqaction - typically used to
-
* allocate special interrupts that are part of the architecture.
-
*/
-
static int
-
__setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
-
{
-
struct irqaction *old, **old_ptr;
-
const char *old_name = NULL;
-
unsigned long flags;
-
int shared = 0;
-
int ret;
-
-
//检查中断描述符其及对应用中断控制器
-
if (!desc)
-
return -EINVAL;
-
-
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.
-
*/
-
//如果指定了IRQF_SAMPLE_RANDOM,意味着设备将对内核随机数熵池有所贡献,rand_initialize_irq
-
//函数处理相应的工作
-
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);
-
}
-
-
/*
-
* Threaded handler ?
-
*/
-
//如果指定了线程函数,则创建内核线程,并将其thread工作队列指针指向新创建的线程
-
if (new->thread_fn) {
-
struct task_struct *t;
-
-
t = kthread_create(irq_thread, new, "irq/%d-%s", irq,
-
new->name);
-
if (IS_ERR(t))
-
return PTR_ERR(t);
-
/*
-
* We keep the reference to the task struct even if
-
* the thread dies to avoid that the interrupt code
-
* references an already freed task_struct.
-
*/
-
get_task_struct(t);
-
new->thread = t;
-
}
-
-
/*
-
* The following block of code has to be executed atomically
-
*/
-
spin_lock_irqsave(&desc->lock, flags);
-
old_ptr = &desc->action;
-
old = *old_ptr;
-
//考虑到一个事实,中断描述符的action链上,可能一个也没有,可能已经注册了一个或多个
-
//如果是后者,则需要判断新伙伴是否是允许共享
-
if (old) {
-
/*
-
* 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.
-
*/
-
//这里的验证表明,它使终使用第一个old来匹备,这意味着action链上的所有节点,都拥有相同的类型
-
//后面的IRQF_PERCPU也是同样的道理
-
if (!((old->flags & new->flags) & IRQF_SHARED) ||
-
((old->flags ^ new->flags) & IRQF_TRIGGER_MASK)) {
-
old_name = old->name;
-
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 */
-
//遍历到action链末尾,等待注册,这里循环也是使用了指向指针的指针,主要是为了添加新元素
-
do {
-
old_ptr = &old->next;
-
old = *old_ptr;
-
} while (old);
-
//置共享标志,必须的
-
shared = 1;
-
}
-
-
//如果是共享,则仅需要验证新的action的类型与中断描述符是否一致即可。
-
//否则,这意味着中断描述符的action上一无所有,这是一个新伙计,则需要通过新的action,为中断描符述设置一些标志位、状态位等诸如此类
-
if (!shared) {
-
-
irq_chip_set_defaults(desc->chip);
-
-
init_waitqueue_head(&desc->wait_for_threads);
-
-
/* Setup the type (level, edge polarity) if configured: */
-
if (new->flags & IRQF_TRIGGER_MASK) {
-
ret = __irq_set_trigger(desc, irq,
-
new->flags & IRQF_TRIGGER_MASK);
-
-
if (ret)
-
goto out_thread;
-
} else
-
compat_irq_chip_set_default_handler(desc);
-
#if defined(CONFIG_IRQ_PER_CPU)
-
if (new->flags & IRQF_PERCPU)
-
desc->status |= IRQ_PER_CPU;
-
#endif
-
-
desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |
-
IRQ_INPROGRESS | IRQ_SPURIOUS_DISABLED);
-
-
if (!(desc->status & IRQ_NOAUTOEN)) {
-
desc->depth = 0;
-
desc->status &= ~IRQ_DISABLED;
-
desc->chip->startup(irq);
-
} else
-
/* Undo nested disables: */
-
desc->depth = 1;
-
-
/* Exclude IRQ from balancing if requested */
-
if (new->flags & IRQF_NOBALANCING)
-
desc->status |= IRQ_NO_BALANCING;
-
-
/* Set default affinity mask once everything is setup */
-
setup_affinity(irq, desc);
-
-
} else if ((new->flags & IRQF_TRIGGER_MASK)
-
&& (new->flags & IRQF_TRIGGER_MASK)
-
!= (desc->status & IRQ_TYPE_SENSE_MASK)) {
-
/* hope the handler works with the actual trigger mode... */
-
pr_warning("IRQ %d uses trigger mode %d; requested %d\n",
-
irq, (int)(desc->status & IRQ_TYPE_SENSE_MASK),
-
(int)(new->flags & IRQF_TRIGGER_MASK));
-
}
-
-
//设置对中断号
-
new->irq = irq;
-
//注册之
-
*old_ptr = new;
-
-
/* Reset broken irq detection when installing new handler */
-
desc->irq_count = 0;
-
desc->irqs_unhandled = 0;
-
-
/*
-
* Check whether we disabled the irq via the spurious handler
-
* before. Reenable it and give it another chance.
-
*/
-
if (shared && (desc->status & IRQ_SPURIOUS_DISABLED)) {
-
desc->status &= ~IRQ_SPURIOUS_DISABLED;
-
__enable_irq(desc, irq, false);
-
}
-
-
spin_unlock_irqrestore(&desc->lock, flags);
-
-
/*
-
* Strictly no need to wake it up, but hung_task complains
-
* when no hard interrupt wakes the thread up.
-
*/
-
//如果有内核线程,唤醒之
-
if (new->thread)
-
wake_up_process(new->thread);
-
-
//注册proc
-
register_irq_proc(irq, desc);
-
new->dir = NULL;
-
register_handler_proc(irq, new);
-
-
return 0;
-
-
mismatch:
-
#ifdef CONFIG_DEBUG_SHIRQ
-
if (!(new->flags & IRQF_PROBE_SHARED)) {
-
printk(KERN_ERR "IRQ handler type mismatch for IRQ %d\n", irq);
-
if (old_name)
-
printk(KERN_ERR "current handler: %s\n", old_name);
-
dump_stack();
-
}
-
#endif
-
ret = -EBUSY;
-
-
out_thread:
-
spin_unlock_irqrestore(&desc->lock, flags);
-
if (new->thread) {
-
struct task_struct *t = new->thread;
-
-
new->thread = NULL;
-
if (likely(!test_bit(IRQTF_DIED, &new->thread_flags)))
-
kthread_stop(t);
-
put_task_struct(t);
-
}
-
return ret;
-
}
|