ARM 裸机程序里对异常的处理过程：
- 按键按下。
- CPU 发生中断。程序会强制的跳到异常向量处执行（中断是异常的一种）。
- “入口函数”是一条跳转指令。跳到某个函数：
- 保存被中断处的现场（各种寄存器的值）。
- 执行中断处理函数。
- 恢复被中断的现场。
LINUX 内核中断的处理过程分析：
程序要先设置异常入口。在head.S中可以看到，异常入口是0x18
@ 0x18:中断模式的向量地址
b HandleIRQ
中断后跳到0x18处开始执行。再跳转（b）到函数HandleIRQ处执行。
ARM 架构的 CPU 的异常向量基址可以是 0x0000 0000,也可以是 0xffff0000，LINUX 内核使用后者。这个地址并不代表实际的内存，是虚拟地址。当建立了虚拟地址与物理地址间的映射后，得将那些异常向量，即相当于把 head.S 中那些跳转指令（如:HandleSWI 等）复制拷贝到这个 0xffff0000 这个地址处去。这个过程是在 trap_init 这个函数里做：
arch/arm/kernel/traps.c
void __init trap_init(void)
{
unsigned long vectors = CONFIG_VECTORS_BASE;//在 linux 源码顶层目录下：less .config, 搜索 "CONFIG_VECTORS_BASE" , 可看到其值为0xffff0000
extern char __stubs_start[], __stubs_end[];
extern char __vectors_start[], __vectors_end[];
extern char __kuser_helper_start[], __kuser_helper_end[];
int kuser_sz = __kuser_helper_end - __kuser_helper_start;
/*
* Copy the vectors, stubs and kuser helpers (in entry-armv.S)
* into the vector page, mapped at 0xffff0000, and ensure these
* are visible to the instruction stream.
*/
//将异常向量复制到 0xffff0000 处,将 __vectors_start, __vectors_end - __vectors_start 这段代码拷贝到 vectors 来。vectors 是“CONFIG_VECTORS_BASE” 是个配置项（内核的配置选项）。
memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start);
memcpy((void *)vectors + 0x200, __stubs_start, __stubs_end - __stubs_start);
memcpy((void *)vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);
/*
* Copy signal return handlers into the vector page, and
* set sigreturn to be a pointer to these.
*/
memcpy((void *)KERN_SIGRETURN_CODE, sigreturn_codes,
sizeof(sigreturn_codes));
flush_icache_range(vectors, vectors + PAGE_SIZE);
modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
}
__vectors_start在arch/arm/kernel/entry-armv.s里面,它也是一些跳转指令。跟单片机的跳转类似。
__vectors_start:
swi SYS_ERROR0
b vector_und + stubs_offset
ldr pc, .LCvswi + stubs_offset
b vector_pabt + stubs_offset
b vector_dabt + stubs_offset
b vector_addrexcptn + stubs_offset
b vector_irq + stubs_offset
b vector_fiq + stubs_offset
.globl __vectors_end
__vectors_end:
.data
.globl cr_alignment
.globl cr_no_alignment
当发生未定义指令异常vector_und的话，会跳转到 vector_und + stubs_offset 处。
这个 vector_und 地址标号是一个宏：
.macro vector_stub, name, mode, correction=0
/*
* Undef instr entry dispatcher
* Enter in UND mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
*/
vector_stub und, UND_MODE
//宏：
/*
* Vector stubs.
*
* This code is copied to 0xffff0200 so we can use branches in the
* vectors, rather than ldr's. Note that this code must not
* exceed 0x300 bytes.
*
* Common stub entry macro:
* Enter in IRQ mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
*
* SP points to a minimal amount of processor-private memory, the address
* of which is copied into r0 for the mode specific abort handler.
*/
.macro vector_stub, name, mode, correction=0
.align 5
vector_\name:
.if \correction
sub lr, lr, #\correction
.endif
@
@ Save r0, lr_ (parent PC) and spsr_
@ (parent CPSR)
@
stmia sp, {r0, lr} @ save r0, lr
mrs lr, spsr
str lr, [sp, #8] @ save spsr
@
@ Prepare for SVC32 mode. IRQs remain disabled.
@
mrs r0, cpsr
eor r0, r0, #(\mode ^ SVC_MODE)
msr spsr_cxsf, r0
@
@ the branch table must immediately follow this code
@
and lr, lr, #0x0f
mov r0, sp
ldr lr, [pc, lr, lsl #2]
movs pc, lr @ branch to handler in SVC mode
.endm
将宏展开：
/*
* Undef instr entry dispatcher
* Enter in UND mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
*/
vector_stub und, UND_MODE
//宏：
/*
* Vector stubs.
*
* This code is copied to 0xffff0200 so we can use branches in the
* vectors, rather than ldr's. Note that this code must not
* exceed 0x300 bytes.
*
* Common stub entry macro:
* Enter in IRQ mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
*
* SP points to a minimal amount of processor-private memory, the address
* of which is copied into r0 for the mode specific abort handler.
*/
.macro vector_stub, name, mode, correction=0
.align 5
vector_und://展开看到，就是定义了这么一个标号vector_und
@//保存现场
@ Save r0, lr_ (parent PC) and spsr_
@ (parent CPSR)
@
stmia sp, {r0, lr} @ save r0, lr
mrs lr, spsr
str lr, [sp, #8] @ save spsr
@//转换到管理模式
@ Prepare for SVC32 mode. IRQs remain disabled.
@
mrs r0, cpsr
eor r0, r0, #(\mode ^ SVC_MODE)
msr spsr_cxsf, r0
@//下面又是下一级的跳转，根据跳转表跳转。
@ the branch table must immediately follow this code
@
and lr, lr, #0x0f
mov r0, sp
ldr lr, [pc, lr, lsl #2]
movs pc, lr @ branch to handler in SVC mode
.endm
//跳转表：
/*
* Undef instr entry dispatcher
* Enter in UND mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
*/
vector_stub und, UND_MODE
.long __und_usr @ 0 (USR_26 / USR_32)
.long __und_invalid @ 1 (FIQ_26 / FIQ_32)
.long __und_invalid @ 2 (IRQ_26 / IRQ_32)
.long __und_svc @ 3 (SVC_26 / SVC_32)
.long __und_invalid @ 4
.long __und_invalid @ 5
.long __und_invalid @ 6
.long __und_invalid @ 7
.long __und_invalid @ 8
.long __und_invalid @ 9
.long __und_invalid @ a
.long __und_invalid @ b
.long __und_invalid @ c
.long __und_invalid @ d
.long __und_invalid @ e
.long __und_invalid @ f
.align 5
//在这些标号里面，又去保存那些寄存器，做一些处理，处理完后恢复那些寄存器。就是恢复那些被中断的程序。
中断的跳转：
__vectors_start:
swi SYS_ERROR0
b vector_und + stubs_offset
ldr pc, .LCvswi + stubs_offset
b vector_pabt + stubs_offset
b vector_dabt + stubs_offset
b vector_addrexcptn + stubs_offset
b vector_irq + stubs_offset //发生了中断后就会跳到这里来
b vector_fiq + stubs_offset
vector_irq也是一个宏来定义的：
vector_stub irq, IRQ_MODE, 4
//name = irq condition = 4
//展开:
.macro vector_stub, name, mode, correction=0
.align 5
vector_irq:
sub lr, lr, #4 //计算返回地址
@
@ Save r0, lr_ (parent PC) and spsr_
@ (parent CPSR)
@
stmia sp, {r0, lr} @ save r0, lr
mrs lr, spsr
str lr, [sp, #8] @ save spsr
@//转换到管理模式
@ Prepare for SVC32 mode. IRQs remain disabled.
@
mrs r0, cpsr
eor r0, r0, #(\mode ^ SVC_MODE)
msr spsr_cxsf, r0
@//继续跳转
@ the branch table must immediately follow this code
@
and lr, lr, #0x0f
mov r0, sp
ldr lr, [pc, lr, lsl #2]
movs pc, lr @ branch to handler in SVC mode
.endm
//跳转表：
/*
* Interrupt dispatcher
*/
vector_stub irq, IRQ_MODE, 4
.long __irq_usr @ 0 (USR_26 / USR_32) //用户态发生中断，跳到这里
.long __irq_invalid @ 1 (FIQ_26 / FIQ_32)
.long __irq_invalid @ 2 (IRQ_26 / IRQ_32)
.long __irq_svc @ 3 (SVC_26 / SVC_32) //管理模式发生中断，跳到这里
.long __irq_invalid @ 4
.long __irq_invalid @ 5
.long __irq_invalid @ 6
.long __irq_invalid @ 7
.long __irq_invalid @ 8
.long __irq_invalid @ 9
.long __irq_invalid @ a
.long __irq_invalid @ b
.long __irq_invalid @ c
.long __irq_invalid @ d
.long __irq_invalid @ e
.long __irq_invalid @ f
__irq_usr：
__irq_usr:
usr_entry //宏，保存寄存器
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_off
#endif
get_thread_info tsk
#ifdef CONFIG_PREEMPT
ldr r8, [tsk, #TI_PREEMPT] @ get preempt count
add r7, r8, #1 @ increment it
str r7, [tsk, #TI_PREEMPT]
#endif
irq_handler //宏，最终会调用asm_do_IRQ
#ifdef CONFIG_PREEMPT
ldr r0, [tsk, #TI_PREEMPT]
str r8, [tsk, #TI_PREEMPT]
teq r0, r7
strne r0, [r0, -r0]
#endif
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_on
#endif
mov why, #0
b ret_to_user
.ltorg
.align 5
irq_handler：
/*
* Interrupt handling. Preserves r7, r8, r9
*/
.macro irq_handler
get_irqnr_preamble r5, lr
1: get_irqnr_and_base r0, r6, r5, lr
movne r1, sp
@
@ routine called with r0 = irq number, r1 = struct pt_regs *
@
adrne lr, 1b
bne asm_do_IRQ
asm_do_IRQ：
/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);
struct irq_desc *desc = irq_desc + irq;
/*
* 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);
/* AT91 specific workaround */
irq_finish(irq);
irq_exit();
set_irq_regs(old_regs);
}
linux 内核中处理异常的流程，最后调用到 "asm_do_IRQ"
//异常向量:
__vectors_start:
swi SYS_ERROR0
b vector_und + stubs_offset
ldr pc, .LCvswi + stubs_offset
b vector_pabt + stubs_offset
b vector_dabt + stubs_offset
b vector_addrexcptn + stubs_offset
b vector_irq + stubs_offset //发生了中断后就会跳到这里来
b vector_fiq + stubs_offset
//vector_irq ---> __irq_usr ---> irq_handler ---> asm_do_IRQ
ARM架构Linux内核的异常处理体系结构
039 ARM架构Linux内核的异常处理体系结构.png
分析“asm_do_IRQ”
单片机下的中断处理：
- 分辨是哪个中断。
- 调用处理函数（哪个中断就调用哪个处理函数）。
- 清中断。
Linux内核的中断处理与单片机的也差不多。以上单片机的 3 个过程，都是在 asm_do_IRQ 中实现的。
/*
* 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);
struct irq_desc *desc = irq_desc + irq;//中断号作为中断描述数组的索引。irq_desc是一个数组,在handle.c里定义
/*
* 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);//处理
/* AT91 specific workaround */
irq_finish(irq);
irq_exit();
set_irq_regs(old_regs);
}
//irq_desc数组以中断号为索引
//这是一个“中断描述”数组。以中断号“NR_IRQS”为下标。
struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
[0 ... NR_IRQS-1] = {
.status = IRQ_DISABLED,
.chip = &no_irq_chip,
.handle_irq = handle_bad_irq,
.depth = 1,
.lock = __SPIN_LOCK_UNLOCKED(irq_desc->lock),
#ifdef CONFIG_SMP
.affinity = CPU_MASK_ALL
#endif
}
};
static inline void desc_handle_irq(unsigned int irq, struct irq_desc *desc)
{
desc->handle_irq(irq, desc);
}
裸机程序中的 3 过程是在这个“handle_irq”中实现的。
handle_irq 的初始化
desc->handle_irq 是在/kernel/irq/chip.c里__set_irq_handler函数里被赋值的：
void
__set_irq_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,
const char *name)
{
struct irq_desc *desc;
desc = irq_desc + irq;
...
desc->handle_irq = handle;
desc->name = name;
...
}
__set_irq_handler在下面函数中被调用
//include/linux/irq.h
static inline void
set_irq_handler(unsigned int irq, irq_flow_handler_t handle)
{
__set_irq_handler(irq, handle, 0, NULL);
}
set_irq_handler 又在下面函数中被调用
//arch/arm/plat-s3c24xx/irq.c
//从这里跟踪set_irq_handler的执行过程，可跟到__set_irq_handler，是以irq为索引，在desc数组里找到一项，把那一项的handle_irq指向传进来那个handle。显然，在s3c24xx_init_irq里面，就构造了这个数组里面的很多项。
/* s3c24xx_init_irq
*
* Initialise S3C2410 IRQ system
*/
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... */
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 */
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);
set_irq_handler(irqno, handle_level_irq);
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);
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
}
/* setup the cascade irq handlers */
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");
}
Irq_desc[外部中断 0 ~ 3 ]：
｛
Handle_irq = handle_edge_irq;
Chip = s3c_irq_eint0t4;
｝
Irq_desc[外部中断 4 到 外部中断 23]：
｛
Handle_irq = handle_edge_irq;
Chip = s3c_irqext_chip;
｝
以上就是初始化。是在“void __init s3c24xx_init_irq(void)”中实现的。
中断处理 C 函数入口 “asm_do_IRQ”会调用到事先初始的“handle_irq”函数。
handle_edge_irq ： 处理边缘触发的中断
void fastcall
handle_edge_irq(unsigned int irq, struct irq_desc *desc)
{
const unsigned int cpu = smp_processor_id();
spin_lock(&desc->lock);
desc->status &= ~(IRQ_REPLAY | IRQ_WAITING);
/*
* If we're currently running this IRQ, or its disabled,
* we shouldn't process the IRQ. Mark it pending, handle
* the necessary masking and go out
*/
if (unlikely((desc->status & (IRQ_INPROGRESS | IRQ_DISABLED)) || //对错误状态的处理
!desc->action)) {
desc->status |= (IRQ_PENDING | IRQ_MASKED);
mask_ack_irq(desc, irq);
goto out_unlock;
}
kstat_cpu(cpu).irqs[irq]++; //中断次数计数
/* Start handling the irq */
desc->chip->ack(irq); //清中断
/* Mark the IRQ currently in progress.*/
desc->status |= IRQ_INPROGRESS;
do {
struct irqaction *action = desc->action;
irqreturn_t action_ret;
if (unlikely(!action)) { //action 是链表。若此链表为空
desc->chip->mask(irq); //则屏蔽中断
goto out_unlock;
}
/*
* When another irq arrived while we were handling
* one, we could have masked the irq.
* Renable it, if it was not disabled in meantime.
*/
if (unlikely((desc->status &
(IRQ_PENDING | IRQ_MASKED | IRQ_DISABLED)) ==
(IRQ_PENDING | IRQ_MASKED))) {
desc->chip->unmask(irq);
desc->status &= ~IRQ_MASKED;
}
desc->status &= ~IRQ_PENDING;
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, action);//处理中断
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
spin_lock(&desc->lock);
} while ((desc->status & (IRQ_PENDING | IRQ_DISABLED)) == IRQ_PENDING);
desc->status &= ~IRQ_INPROGRESS;
out_unlock:
spin_unlock(&desc->lock);
}
handle_edge_irq
-->desc->chip->ack(irq). 清中断
-->handle_IRQ_event(irq, action). 处理中断
/**
* 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();
do { //取出action链表中的成员，执行action->handler
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;
}
中断处理框架总结
按下按键后
-
CPU 自动进入“异常模式”。调用“异常处理函数”。
//异常向量: __vectors_start: swi SYS_ERROR0 b vector_und + stubs_offset ldr pc, .LCvswi + stubs_offset b vector_pabt + stubs_offset b vector_dabt + stubs_offset b vector_addrexcptn + stubs_offset b vector_irq + stubs_offset //发生了中断后就会跳到这里来 b vector_fiq + stubs_offset //vector_irq ---> __irq_usr ---> irq_handler ---> asm_do_IRQ 在“异常处理函数”中如果跳到 “b vector_irq + stubs_offset” 。 vector_irq是一个宏定义。
调用到列表中的“__irq_usr”，再调用“irq_handler”，这也是一个宏。最终会调用到“asm_do_IRQ”这个 C 函数。
“asm_do_IRQ” 调用 irq_desc[IRQ 中断下标] 取出里面的一项 “handle_irq”
在：linux-2.6.22.6\arch\arm\plat-s3c24xx\Irq.c 中，s3c24xx_init_irq(void)初始化中断时，若是外部中断 0-3，或外部中断 4-23 时，desc->handle_irq(irq, desc)指向“handle_edge_irq 函数
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);
}
“handle_edge_irq”做的事：
① desc->chip->ack() 清中断
② handle_IRQ_event() 处理中断
③ 取出“action”链表中的成员，执行“action->handler”。-
核心在“irq_desc” 结构数组：
分析“irq_desc[]”结构数组：里面有“action 链表”，有“chip”等。
/**
* struct irq_desc - interrupt descriptor
*
* @handle_irq: highlevel irq-events handler [if NULL, __do_IRQ()]
* @chip: low level interrupt hardware access
* @msi_desc: MSI descriptor
* @handler_data: per-IRQ data for the irq_chip methods
* @chip_data: platform-specific per-chip private data for the chip
* methods, to allow shared chip implementations
* @action: the irq action chain
* @status: status information
* @depth: disable-depth, for nested irq_disable() calls
* @wake_depth: enable depth, for multiple set_irq_wake() callers
* @irq_count: stats field to detect stalled irqs
* @irqs_unhandled: stats field for spurious unhandled interrupts
* @lock: locking for SMP
* @affinity: IRQ affinity on SMP
* @cpu: cpu index useful for balancing
* @pending_mask: pending rebalanced interrupts
* @dir: /proc/irq/ procfs entry
* @affinity_entry: /proc/irq/smp_affinity procfs entry on SMP
* @name: flow handler name for /proc/interrupts output
*/
struct irq_desc {
irq_flow_handler_t handle_irq; //函数指针，在前面例子中指向handle_edge_irq()
struct irq_chip *chip; //芯片相关底层处理函数。如指向s3c_irqext_chip
struct msi_desc *msi_desc;
void *handler_data;
void *chip_data;
struct irqaction *action; /* IRQ action list */
unsigned int status; /* IRQ status */
unsigned int depth; /* nested irq disables */
unsigned int wake_depth; /* nested wake enables */
unsigned int irq_count; /* For detecting broken IRQs */
unsigned int irqs_unhandled;
spinlock_t lock;
#ifdef CONFIG_SMP
cpumask_t affinity;
unsigned int cpu;
#endif
#if defined(CONFIG_GENERIC_PENDING_IRQ) || defined(CONFIG_IRQBALANCE)
cpumask_t pending_mask;
#endif
#ifdef CONFIG_PROC_FS
struct proc_dir_entry *dir;
#endif
const char *name;
} ____cacheline_internodealigned_in_smp;
handle_irq:是函数指针。在上面的例子中这个函数指针指向了“handle_edge_irq”。
首先是清中断，然后把链表“action”中的成员取出，一一执行里面的“action->handler”
#endif
struct proc_dir_entry;
struct msi_desc;
/**
* struct irq_chip - hardware interrupt chip descriptor
*
* @name: name for /proc/interrupts
* @startup: start up the interrupt (defaults to ->enable if NULL)
* @shutdown: shut down the interrupt (defaults to ->disable if NULL)
* @enable: enable the interrupt (defaults to chip->unmask if NULL)
* @disable: disable the interrupt (defaults to chip->mask if NULL)
* @ack: start of a new interrupt
* @mask: mask an interrupt source
* @mask_ack: ack and mask an interrupt source
* @unmask: unmask an interrupt source
* @eoi: end of interrupt - chip level
* @end: end of interrupt - flow level
* @set_affinity: set the CPU affinity on SMP machines
* @retrigger: resend an IRQ to the CPU
* @set_type: set the flow type (IRQ_TYPE_LEVEL/etc.) of an IRQ
* @set_wake: enable/disable power-management wake-on of an IRQ
*
* @release: release function solely used by UML
* @typename: obsoleted by name, kept as migration helper
*/
struct irq_chip {
const char *name;
unsigned int (*startup)(unsigned int irq);
void (*shutdown)(unsigned int irq);
void (*enable)(unsigned int irq);
void (*disable)(unsigned int irq);
void (*ack)(unsigned int irq); //清中断
void (*mask)(unsigned int irq);
void (*mask_ack)(unsigned int irq);
void (*unmask)(unsigned int irq);
void (*eoi)(unsigned int irq);
void (*end)(unsigned int irq);
void (*set_affinity)(unsigned int irq, cpumask_t dest);
int (*retrigger)(unsigned int irq);
int (*set_type)(unsigned int irq, unsigned int flow_type);
int (*set_wake)(unsigned int irq, unsigned int on);
/* Currently used only by UML, might disappear one day.*/
#ifdef CONFIG_IRQ_RELEASE_METHOD
void (*release)(unsigned int irq, void *dev_id);
#endif
/*
* For compatibility, ->typename is copied into ->name.
* Will disappear.
*/
const char *typename;
};
struct irqaction {
irq_handler_t handler;
unsigned long flags;
cpumask_t mask;
const char *name;
void *dev_id;
struct irqaction *next;
int irq;
struct proc_dir_entry *dir;
};
写中断处理时，是想要执行自已的中断代码。代码就应该放在“action->handler”这里。用“request_irq()”告诉内核处理函数是什么。
Linux内核的中断处理体系结构
040 Linux内核的中断处理体系结构.png
首先内核中有个数组“irq_desc[]”IRQ 的描述结构数组，这个结构数组是以“中断号”为下标。
结构中有：
- handle_irq:中断入口函数。这个入口函数中，是做清中断，再调用 action 链表中的各种处理函数。
- chip: 指向底层硬件的访问函数，它做屏蔽中断、使能中断，响应中断等。
- action：链表头，它指向“irqaction 结构”，这个结构中存放“handler 用户注册的中断处理函数”等。
我们想使用自已的中断处理函数时，就是在内核的这个中断框架里在其中的“action 链表”中添加进我们的“中断函数”。
分析request_irq：
// 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
*
*/
/*
irq:中断号。
handler：处理函数。
irqflags:上升沿触发，下降沿触发，边沿触发等。指定了快速中断或中断共享等中断处理属性.
*devname：中断名字。通常是设备驱动程序的名称。改值用在 /proc/interrupt 系统 (虚拟) 文件上，或内核发生中断错误时使用。
第 5 个参数 dev_id 可作为共享中断时的中断区别参数，也可以用来指定中断服务函数需要参考的数据地址
*/
int request_irq(unsigned int irq, irq_handler_t handler,
unsigned long irqflags, const char *devname, void *dev_id)
{
struct irqaction *action;
int retval;
#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).
*/
if ((irqflags & IRQF_SHARED) && !dev_id)
return -EINVAL;
if (irq >= NR_IRQS)
return -EINVAL;
if (irq_desc[irq].status & IRQ_NOREQUEST)
return -EINVAL;
if (!handler)
return -EINVAL;
action = kmalloc(sizeof(struct irqaction), GFP_ATOMIC); //分配一个“irqaction”结构。
if (!action)
return -ENOMEM;
//这个申请的结构将传来的 handler 处理函数等都记录下来。
action->handler = handler;
action->flags = irqflags;
cpus_clear(action->mask);
action->name = devname;
action->next = NULL;
action->dev_id = dev_id;
select_smp_affinity(irq);
#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 do this before actually registering it, to make sure that
* a 'real' IRQ doesn't run in parallel with our fake
*/
if (irqflags & IRQF_DISABLED) {
unsigned long flags;
local_irq_save(flags);
handler(irq, dev_id);
local_irq_restore(flags);
} else
handler(irq, dev_id);
}
#endif
retval = setup_irq(irq, action); ///* 设置中断 */
//参 1：要安装中断处理程序的中断号。
//参 2：irq 号中断的中断操作行为描述结构指针。
if (retval)
kfree(action);
return retval;
}
EXPORT_SYMBOL(request_irq);
setup_irq:
/*
* 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;
struct irqaction *old, **p;
const char *old_name = NULL;
unsigned long flags;
int shared = 0;
if (irq >= NR_IRQS)
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.
*/
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
*/
spin_lock_irqsave(&desc->lock, flags);
p = &desc->action; //以中断号为下标，找到“irq_desc[]”数组中的一项。
old = *p;
if (old) {//action 是链表头，判断这个链表开始有没有结构。
/*
* 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.
*/
if (!((old->flags & new->flags) & IRQF_SHARED) || /* 是否是共享中断。若action链表头里挂接了多个项就表明此中断为共享中断 */
//“共享中断”：表示中断来源有很多种，但它们共享同一个引脚。
((old->flags ^ new->flags) & IRQF_TRIGGER_MASK)) {
old_name = old->name;
goto mismatch;//如果之前那个老的 action 结构不是作“共享中断”时，我们就不能将申请的新结构放进这个老的“action”链表中去。就不能再次链接新的结构进去了。就表示出“goto mismatch;”出错
}
#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 */
do {//这是将新的结构放进去。
p = &old->next;
old = *p;
} while (old);
shared = 1;
}
*p = new;
/* Exclude IRQ from balancing */
if (new->flags & IRQF_NOBALANCING)
desc->status |= IRQ_NO_BALANCING;
if (!shared) {
irq_chip_set_defaults(desc->chip);
#if defined(CONFIG_IRQ_PER_CPU)
if (new->flags & IRQF_PERCPU)
desc->status |= IRQ_PER_CPU;
#endif
/* Setup the type (level, edge polarity) if configured: */
if (new->flags & IRQF_TRIGGER_MASK) {
if (desc->chip && desc->chip->set_type)
desc->chip->set_type(irq,//将对应的引脚设置为“中断引脚”（外部中断，中断触发方式）。
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
compat_irq_chip_set_default_handler(desc);
desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |
IRQ_INPROGRESS);
if (!(desc->status & IRQ_NOAUTOEN)) {
desc->depth = 0;
desc->status &= ~IRQ_DISABLED;
if (desc->chip->startup)
desc->chip->startup(irq); //“使能中断
else
desc->chip->enable(irq); //“使能中断
} else
/* Undo nested disables: */
desc->depth = 1;
}
/* Reset broken irq detection when installing new handler */
desc->irq_count = 0;
desc->irqs_unhandled = 0;
spin_unlock_irqrestore(&desc->lock, flags);
new->irq = irq;
register_irq_proc(irq);
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
spin_unlock_irqrestore(&desc->lock, flags);
return -EBUSY;
}
//chip 结构：
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);
}
static struct irq_chip s3c_irq_eint0t4 = {
.name = "s3c-ext0",
.ack = s3c_irq_ack,
.mask = s3c_irq_mask,
.unmask = s3c_irq_unmask,
.set_wake = s3c_irq_wake,
.set_type = s3c_irqext_type,
};
int
s3c_irqext_type(unsigned int irq, unsigned int type)
{
void __iomem *extint_reg;
void __iomem *gpcon_reg;
unsigned long gpcon_offset, extint_offset;
unsigned long newvalue = 0, value;
//若为外部中断 0-3，则将上面的相关引脚配置成中断引脚
if ((irq >= IRQ_EINT0) && (irq <= IRQ_EINT3))
{
gpcon_reg = S3C2410_GPFCON;
extint_reg = S3C24XX_EXTINT0;
gpcon_offset = (irq - IRQ_EINT0) * 2;
extint_offset = (irq - IRQ_EINT0) * 4;
}
else if ((irq >= IRQ_EINT4) && (irq <= IRQ_EINT7))
{
gpcon_reg = S3C2410_GPFCON;
extint_reg = S3C24XX_EXTINT0;
gpcon_offset = (irq - (EXTINT_OFF)) * 2;
extint_offset = (irq - (EXTINT_OFF)) * 4;
}
else if ((irq >= IRQ_EINT8) && (irq <= IRQ_EINT15))
{
gpcon_reg = S3C2410_GPGCON;
extint_reg = S3C24XX_EXTINT1;
gpcon_offset = (irq - IRQ_EINT8) * 2;
extint_offset = (irq - IRQ_EINT8) * 4;
}
else if ((irq >= IRQ_EINT16) && (irq <= IRQ_EINT23))
{
gpcon_reg = S3C2410_GPGCON;
extint_reg = S3C24XX_EXTINT2;
gpcon_offset = (irq - IRQ_EINT8) * 2;
extint_offset = (irq - IRQ_EINT16) * 4;
} else
return -1;
/* Set the GPIO to external interrupt mode */
value = __raw_readl(gpcon_reg);
value = (value & ~(3 << gpcon_offset)) | (0x02 << gpcon_offset);
__raw_writel(value, gpcon_reg);
/* Set the external interrupt to pointed trigger type */
switch (type)//根据request_irq()参3的irqflags标志来判断中断触发方式
{
case IRQT_NOEDGE:
printk(KERN_WARNING "No edge setting!\n");
break;
case IRQT_RISING: //上升沿触发
newvalue = S3C2410_EXTINT_RISEEDGE;
break;
case IRQT_FALLING: //下降沿触发
newvalue = S3C2410_EXTINT_FALLEDGE;
break;
case IRQT_BOTHEDGE: //双边沿触发
newvalue = S3C2410_EXTINT_BOTHEDGE;
break;
case IRQT_LOW: //低电平触发
newvalue = S3C2410_EXTINT_LOWLEV;
break;
case IRQT_HIGH://高电平触发
newvalue = S3C2410_EXTINT_HILEV;
break;
default:
printk(KERN_ERR "No such irq type %d", type);
return -1;
}
value = __raw_readl(extint_reg);
value = (value & ~(7 << extint_offset)) | (newvalue << extint_offset);
__raw_writel(value, extint_reg);
return 0;
}
注册用户中断处理函数：
request_irq(中断号,处理函数,硬件触发试,中断名字,dev_id).
{
分配一个 irqaction 结构。结构指向 request_irq 中的参数。
将上面的 irqaction 结构放到 irq_desc[irq]数组项中的 action 链表中。
设置引脚成为中断引脚。
使能中断。
}
分析卸载中断free_irq：
/**
* free_irq - free an interrupt
* @irq: Interrupt line to free
* @dev_id: Device identity to free
*
* Remove an interrupt handler. The handler is removed and if the
* interrupt line is no longer in use by any driver it is disabled.
* On a shared IRQ the caller must ensure the interrupt is disabled
* on the card it drives before calling this function. The function
* does not return until any executing interrupts for this IRQ
* have completed.
*
* This function must not be called from interrupt context.
*/
void free_irq(unsigned int irq, void *dev_id)
{
struct irq_desc *desc;
struct irqaction **p;
unsigned long flags;
irqreturn_t (*handler)(int, void *) = NULL;
WARN_ON(in_interrupt());
if (irq >= NR_IRQS)
return;
desc = irq_desc + irq; /* 找到数组项 */
spin_lock_irqsave(&desc->lock, flags);
p = &desc->action;
for (;;) {
struct irqaction *action = *p;
if (action) {
struct irqaction **pp = p;
p = &action->next;
if (action->dev_id != dev_id) /* 判断dev_id是否为free_irq()传来的参2 */
continue;
/* Found it - now remove it from the list of entries */
*pp = action->next;
/* Currently used only by UML, might disappear one day.*/
#ifdef CONFIG_IRQ_RELEASE_METHOD
if (desc->chip->release)
desc->chip->release(irq, dev_id);
#endif
if (!desc->action) {///* 若链表空了，就禁止或屏蔽这个chip */
desc->status |= IRQ_DISABLED;
if (desc->chip->shutdown)
desc->chip->shutdown(irq);
else
desc->chip->disable(irq);
}
spin_unlock_irqrestore(&desc->lock, flags);
unregister_handler_proc(irq, action);
/* Make sure it's not being used on another CPU */
synchronize_irq(irq);
if (action->flags & IRQF_SHARED)
handler = action->handler;
kfree(action);
return;
}
printk(KERN_ERR "Trying to free already-free IRQ %d\n", irq);
spin_unlock_irqrestore(&desc->lock, flags);
return;
}
#ifdef CONFIG_DEBUG_SHIRQ
if (handler) {
/*
* It's a shared IRQ -- the driver ought to be prepared for it
* to happen even now it's being freed, so let's make sure....
* We do this after actually deregistering it, to make sure that
* a 'real' IRQ doesn't run in parallel with our fake
*/
handler(irq, dev_id);
}
#endif
}
EXPORT_SYMBOL(free_irq);
卸载中断处理函数：
void free_irq(unsigned int irq, void *dev_id)
{
将其从 action 链表中删除结构。
禁止中断（在 action 链表中没有成员结构 irqacton 时了，要是共享中断中删除一个结构还有其他结构时，中断也不会禁止）。
}