arm linux 下中斷流程簡要分析初始化

因此，在中斷初始化的時候我們要做的就是在IRQ和FIQ的位置處放置我們的中斷處理函數(shù)地址或跳轉(zhuǎn)語句跳轉(zhuǎn)到我們的中斷處理函數(shù)。這個過程是在trap_init中完成的，而他由start_kernel()調(diào)用。

arch/arm/kernel/traps.c:

void __init trap_init(void)

{

unsigned long vectors = CONFIG_VECTORS_BASE;/*跳轉(zhuǎn)表的存放位置（即上面那表的存放位置）*/

/*這些都在entry-armv.S下定義*/

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.

*/

/*跳轉(zhuǎn)表內(nèi)容到指定的位置*/

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);

}

上面這個函數(shù)主要就是在CONFIG_VECTORS_BASE處設(shè)置好那張?zhí)D(zhuǎn)表，CONFIG_VECTORS_BASE在autoconf.h中定義(該文件自動成生)，值為0xffff0000,而CP15下的r1[13]在系統(tǒng)啟動的時候在匯編部分就已經(jīng)設(shè)置好了。

接下來我們就看下__vectors_start，__vectors_end，__stubs_start，__stubs_end之間的內(nèi)容。

arch/arm/kernel/entry-armv.S:

.globl__vectors_start

__vectors_start:

swiSYS_ERROR0

bvector_und + stubs_offset

ldrpc, .LCvswi + stubs_offset

bvector_pabt + stubs_offset

bvector_dabt + stubs_offset

bvector_addrexcptn + stubs_offset

bvector_irq + stubs_offset

bvector_fiq + stubs_offset

.globl__vectors_end

__vectors_end:

.data

看到了吧， 就是那張?zhí)D(zhuǎn)表。vector_irq，vector_fiq等函數(shù)我們后面在分析，他們就定義在__stubs_start，__stubs_end中。

至此經(jīng)過traps_init后，在0xffff0000處的跳轉(zhuǎn)表就形成了。當(dāng)產(chǎn)生IRQ時，將調(diào)用bvector_irq + stubs_offset

在系統(tǒng)初始化的時候還會調(diào)用init_IRQ函數(shù)(也由start_kernel調(diào)用)，它初始化了一個全局中斷描述符表(該表保存了每個中斷的所有屬性信息)。并調(diào)用特定平臺的中斷初始化函數(shù)。

arm/arm/kernel/Irq.c:

void __init init_IRQ(void)

{

int irq;

/*初始化中斷描述符表*/

for (irq = 0; irq < NR_IRQS; irq++)

irq_desc[irq].status |= IRQ_NOREQUEST | IRQ_DELAYED_DISABLE |

IRQ_NOPROBE;

#ifdef CONFIG_SMP

bad_irq_desc.affinity = CPU_MASK_ALL;

bad_irq_desc.cpu = smp_processor_id();

#endif

init_arch_irq();/*特定平臺的中斷初始化*/

}

系統(tǒng)中總共有NR_IRQS個中斷，并且每個中斷都有一個中斷描述符，保存在irq_desc中，該描述符保存了該中斷的所有屬性信息。

對于平臺smdk2410來說init_arch_irq()就是s3c24xx_init_irq()函數(shù),這是在setup_arch()里面賦值的。

后面的內(nèi)容我們都以中斷號：IRQ_WDT為例來講解：

arch/arm/mach-s3c2410/Irq.c:

/* 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... */

/*先清掉所有的pending標(biāo)志位，該位代表是否系統(tǒng)中觸發(fā)了一個中斷*/

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 */

/*注冊主要的中斷*/

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, do_level_IRQ);

break;

case IRQ_RESERVED6:

case IRQ_RESERVED24:

/* no IRQ here */

break;

default:/*IRQ_WDT就是這條通路*/

//irqdbf("registering irq %d (s3c irq)/n", irqno);

set_irq_chip(irqno, &s3c_irq_chip); /*為中斷號設(shè)置chip*/

set_irq_handler(irqno, do_edge_IRQ); /*設(shè)置中斷例程*/

set_irq_flags(irqno, IRQF_VALID);/*設(shè)置中斷ready的標(biāo)記*/

}

}

/* setup the cascade irq handlers */

set_irq_chained_handler(IRQ_EINT4t7, s3c_irq_demux_extint);

set_irq_chained_handler(IRQ_EINT8t23, s3c_irq_demux_extint);

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, do_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, do_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, do_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, do_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, do_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, do_edge_IRQ);

set_irq_flags(irqno, IRQF_VALID);

}

irqdbf("s3c2410: registered interrupt handlers/n");

}

上面這個函數(shù)結(jié)合s3c2410的data sheet很好理解，就是注冊各個必要的中斷，注意這里為每個中斷號注冊的中斷例程只是個整體的函數(shù)，該函數(shù)只是處理一些共性的操作如清中斷標(biāo)記位等，他會進一步調(diào)用我們注冊的中斷例程來處理特定的中斷。如何注冊中斷會在后面分析。

這個初始化函數(shù)調(diào)用了很多與中斷相關(guān)的函數(shù)，我們逐個分析：

先看set_irq_chip

kernel/irq/chip.c:

/

*set_irq_chip - set the irq chip for an irq

*@irq:irq number

*@chip:pointer to irq chip description structure

*/

/*為某個中斷號設(shè)置一個chip*/

int set_irq_chip(unsigned int irq, struct irq_chip *chip)

{

struct irq_desc *desc;

unsigned long flags;

if (irq >= NR_IRQS) {

printk(KERN_ERR "Trying to install chip for IRQ%d/n", irq);

WARN_ON(1);

return -EINVAL;

}

if (!chip)

chip = &no_irq_chip;

desc = irq_desc + irq;/*獲取保存該中斷的中斷描述符*/

spin_lock_irqsave(&desc->lock, flags);

irq_chip_set_defaults(chip); /*為chip設(shè)置一些默認(rèn)的enable,disable函數(shù)*/

desc->chip = chip;/*為中斷保存chip對象*/

/*

* For compatibility only:

*/

desc->chip = chip;

spin_unlock_irqrestore(&desc->lock, flags);

return 0;

}

為特定中斷號初始化好chip對象，表示該中斷號由這個chip控制，后面會調(diào)用到該中斷號所屬chip的相關(guān)函數(shù)，各個中斷的chip是不同的,以IRQ_WDT為例，它的chip是s3c_irq_chip。

arch/arm/mach-s3c2410/Irq.c:

static struct irqchip s3c_irq_chip = {

.ack= s3c_irq_ack,

.mask= s3c_irq_mask,

.unmask= s3c_irq_unmask,

.set_wake= s3c_irq_wake

};

在看irq_chip_set_defaults

kernel/irq/Chip.c:

/*

* Fixup enable/disable function pointers

*/

void irq_chip_set_defaults(struct irq_chip *chip)

{

if (!chip->enable)

chip->enable = default_enable;

if (!chip->disable)

chip->disable = default_disable;

if (!chip->startup)

chip->startup = default_startup;

if (!chip->shutdown)

chip->shutdown = chip->disable;

if (!chip->name)

chip->name = chip->typename;

}

很顯然，如果chip沒有相應(yīng)的操作函數(shù)，則就給chip賦默認(rèn)的操作函數(shù)。

我們接著看set_irq_handler()

include/linux/Irq.h:

static inline void

set_irq_handler(unsigned int irq,

void fastcall (*handle)(unsigned int, struct irq_desc *,

struct pt_regs *))

{

__set_irq_handler(irq, handle, 0);

}

kernel/irq/Chip.c:

void

__set_irq_handler(unsigned int irq,

void fastcall (*handle)(unsigned int, irq_desc_t *,

struct pt_regs *),

int is_chained)

{

struct irq_desc *desc;

unsigned long flags;

if (irq >= NR_IRQS) { /*參數(shù)檢查*/

printk(KERN_ERR

"Trying to install type control for IRQ%d/n", irq);

return;

}

desc = irq_desc + irq; /*獲取中斷描述符的存儲地址*/

if (!handle)

handle = handle_bad_irq;/*賦默認(rèn)的中斷handle*/

if (desc->chip == &no_irq_chip) {

printk(KERN_WARNING "Trying to install %sinterrupt handler "

"for IRQ%d/n", is_chained ? "chained " : " ", irq);

/*

* Some ARM implementations install a handler for really dumb

* interrupt hardware without setting an irq_chip. This worked

* with the ARM no_irq_chip but the check in setup_irq would

* prevent us to setup the interrupt at all. Switch it to

* dummy_irq_chip for easy transition.

*/

desc->chip = &dummy_irq_chip;/*賦默認(rèn)的chip*/

}

spin_lock_irqsave(&desc->lock, flags);

/* Uninstall? */

if (handle == handle_bad_irq) {

if (desc->chip != &no_irq_chip) {

desc->chip->mask(irq);

desc->chip->ack(irq);

}

desc->status |= IRQ_DISABLED;/*沒有中斷例程則disable掉該中斷*/

desc->depth = 1;

}

desc->handle_irq = handle;/*保存中斷例程，對于IRQ_WDT來說則是do_edge_IRQ */

/*由上面的調(diào)用可知，is_chained始終等于0*/

if (handle != handle_bad_irq && is_chained) {

desc->status &= ~IRQ_DISABLED;

desc->status |= IRQ_NOREQUEST | IRQ_NOPROBE;

desc->depth = 0;

desc->chip->unmask(irq);

}

spin_unlock_irqrestore(&desc->lock, flags);

}

上面這個函數(shù)就是為特定的中斷設(shè)置好一個中斷處理例程(這里的例程可不是我們request_irq注冊的例程喔)。

接著看set_irq_flags()

arch/arm/kernel/Irq.c:

void set_irq_flags(unsigned int irq, unsigned int iflags)

{

struct irqdesc *desc;

unsigned long flags;

if (irq >= NR_IRQS) {

printk(KERN_ERR "Trying to set irq flags for IRQ%d/n", irq);

return;

}

desc = irq_desc + irq;

spin_lock_irqsave(&desc->lock, flags);

desc->status |= IRQ_NOREQUEST | IRQ_NOPROBE | IRQ_NOAUTOEN;

if (iflags & IRQF_VALID)

desc->status &= ~IRQ_NOREQUEST;/*清掉IRQ_NOREQUEST標(biāo)記*/

if (iflags & IRQF_PROBE)

desc->status &= ~IRQ_NOPROBE;

if (!(iflags & IRQF_NOAUTOEN))

desc->status &= ~IRQ_NOAUTOEN;

spin_unlock_irqrestore(&desc->lock, flags);

}

該函數(shù)主要是為特定的中斷設(shè)置相應(yīng)的狀態(tài)標(biāo)記， 而這里我們調(diào)用它的目的就是清掉IRQ_NOREQUEST標(biāo)記，告訴系統(tǒng)該中斷已經(jīng)可以被申請使用了，中斷在申請的時候會查看是否有IRQ_NOREQUEST標(biāo)記，如有則表面該中斷還不能使用。而初始化的時候所有的中斷都有這個標(biāo)記。