浅谈分析Arm linux 内核移植及系统初始化的过程二

4.1. 处理器、设备4.2. 描述
设备描述主要两个结构体完成：struct resource和struct platform_device。
先来看看着两个结构体的定义：
struct resource {
resource_size_t start;
resource_size_t end;
const char *name;
unsigned long flags;
struct resource *parent, *sibling, *child;
};
Resource结构体主要是描述了设备在系统中的起止地址、名称、标志以及为了链式描述方便指向本结构体类型的指针。Resource定义的实例将被添加到platform_device结构体对象中去。
struct platform_device {
const char * name;
u32 id;
struct device dev;
u32 num_resources;
struct resource * resource;
};
Platform_device结构体包括结构体的名称、ID号、平台相关的信息、设备的数目以及上面定义的resource信息。Platform_device结构对象将被直接通过设备操作函数注册导系统中去。具体注册和注销过程在下一节介绍。
4.3. 处理器、设备4.4. 操作
(1) int platform_device_register(struct platform_device * pdev)；    注册设备
(2) void platform_device_unregister(struct platform_device * pdev)； 注销设备
(3) int platform_add_devices(struct platform_device **devs, int num)；添加设备，通过调用上面两个函数实现。
4.5. 添加Nand flash设备4.6. 
下面以nand flash 设备的描述为例，具体介绍下设备的描述和注册过程。
// resource结构体实例s3c_nand_resource 对nand flash 控制器描述，包括控制器的起止地址和标志。
static struct resource s3c_nand_resource[] = {
[0] = {
.start = S3C2410_PA_NAND,
.end   = S3C2410_PA_NAND + S3C24XX_SZ_NAND - 1,
.flags = IORESOURCE_MEM,
}
};
//platform_device结构体实例s3c_device_nand定义了设备的名称、ID号并把resource对象作为其成员之一。
struct platform_device s3c_device_nand = {
.name   = "s3c2410-nand",
.id   = -1,
.num_resources   = ARRAY_SIZE(s3c_nand_resource),
.resource   = s3c_nand_resource,
};
// nand flash 的分区情况，由mtd_partition结构体定义。
static struct mtd_partition smdk_default_nand_part[] = {
[0] = {
.name = "Boot Agent",
.size = SZ_16K,
.offset = 0,
},
[1] = {
.name = "S3C2410 flash partition 1",
.offset = 0,
.size = SZ_2M,
},
[2] = {
.name = "S3C2410 flash partition 2",
.offset = SZ_4M,
.size = SZ_4M,
},
[3] = {
.name = "S3C2410 flash partition 3",
.offset = SZ_8M,
.size = SZ_2M,
},
[4] = {
.name = "S3C2410 flash partition 4",
 .offset = SZ_1M * 10,
.size = SZ_4M,
},
[5] = {
.name = "S3C2410 flash partition 5",
.offset = SZ_1M * 14,
.size = SZ_1M * 10,
},
[6] = {
.name = "S3C2410 flash partition 6",
.offset = SZ_1M * 24,
.size = SZ_1M * 24,
},
[7] = {
.name = "S3C2410 flash partition 7",
.offset = SZ_1M * 48,
.size = SZ_16M,
}
};

static struct s3c2410_nand_set smdk_nand_sets[] = {
[0] = {
.name = "NAND",
.nr_chips = 1,
.nr_partitions = ARRAY_SIZE(smdk_default_nand_part),
.partitions = smdk_default_nand_part,
},
};

/* choose a set of timings which should suit most 512Mbit
 * chips and beyond.
*/

static struct s3c2410_platform_nand smdk_nand_info = {
.tacls = 20,
.twrph0 = 60,
.twrph1 = 20,
.nr_sets = ARRAY_SIZE(smdk_nand_sets),
.sets = smdk_nand_sets,
};

/* devices we initialise */
// 最后将nand flash 设备加入到系统即将注册的设备集合中。 
static struct platform_device __initdata *smdk_devs[] = {
&s3c_device_nand,
&smdk_led4,
&smdk_led5,
&smdk_led6,
&smdk_led7,
};

然后通过smdk_machine_init()函数，调用设备添加函数platform_add_devices(smdk_devs, ARRAY_SIZE(smdk_devs)) 完成设备的注册。具体过程参见系统初始化的相关部分。
5. 系统初始化
5.1. 系统初始化的主干线
Start_kernel() èsetup_arch() èreset_init() è kernel_thread(init …) è init() è do_basic_setup() èdriver_init() è do_initcall()

Start_kernel()函数负责初始化内核各个子系统，最后调用reset_init()，启动一个叫做init的内核线程，继续初始化。Start_kernel()函数在init/main.c中实现。

asmlinkage void __init start_kernel(void)
{
char * command_line;
extern struct kernel_param __start___param[], __stop___param[];

smp_setup_processor_id();

/*
 * Need to run as early as possible, to initialize the
 * lockdep hash:
 */
lockdep_init();

local_irq_disable();
early_boot_irqs_off();
early_init_irq_lock_class();

/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */
lock_kernel();
boot_cpu_init();
page_address_init();
printk(KERN_NOTICE);
printk(linux_banner);
setup_arch(&command_line); 
 //setup processor and machine and destinate some pointers for do_initcalls() s

5、浅谈分析Arm linux 内核移植及系统初始化的过程 咨询QQ:313807838
 // for example init_machine pointer is initialized with smdk_machine_init() , and //init_machine() is called by customize_machine(), and the is processed by //arch_initcall(fn). Therefore  smdk_machine_init() is issured.    by edwin
setup_per_cpu_areas();
smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */

/*
 * Set up the scheduler prior starting any interrupts (such as the
 * timer interrupt). Full topology setup happens at smp_init()
 * time - but meanwhile we still have a ing scheduler.
 */
sched_init();
/*
 * Disable preemption - early bootup scheduling is extremely
 * fragile until we cpu_idle() for the first time.
 */
preempt_disable();
build_all_zonelists();
page_alloc_init();
printk(KERN_NOTICE "Kernel command line: %sn", saved_command_line);
parse_early_param();
parse_args("Booting kernel", command_line, __start___param,
   __stop___param - __start___param,
   &unknown_bootoption);
sort_main_extable();
unwind_init();
trap_init();
rcu_init();
init_IRQ();
pidhash_init();
init_timers();
hrtimers_init();
softirq_init();
timekeeping_init();
time_init();
profile_init();
if (!irqs_disabled())
printk("start_kernel(): bug: interrupts were enabled earlyn");
early_boot_irqs_on();
local_irq_enable();

/*
 * HACK ALERT! This is early. We're enabling the console before
 * we've done PCI setups etc, and console_init() must be aware of
 * this. But we do want output early, in case something goes wrong.
 */
console_init();
if (panic_later)
panic(panic_later, panic_param);

lockdep_info();

/*
 * Need to run this when irqs are enabled, because it wants
 * to self-test [hard/soft]-irqs on/off lock inversion bugs
 * too:
 */
locking_selftest();

#ifdef CONFIG_BLK_DEV_INITRD
if (initrd_start && !initrd_below_start_ok &&
initrd_start < min_low_pfn << PAGE_SHIFT) {
printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - "
 
6、浅谈分析Arm linux 内核移植及系统初始化的过程  咨询QQ：313807838
     "disabling it.n",initrd_start,min_low_pfn << PAGE_SHIFT);
initrd_start = 0;
}
#endif
vfs_caches_init_early();
cpuset_init_early();
mem_init();
kmem_cache_init();
setup_per_cpu_pageset();
numa_policy_init();
if (late_time_init)
late_time_init();
calibrate_delay();
pidmap_init();
pgtable_cache_init();
prio_tree_init();
anon_vma_init();
#ifdef CONFIG_X86
if (efi_enabled)
efi_enter_virtual_mode();
#endif
fork_init(num_physpages);
proc_caches_init();
buffer_init();
unnamed_dev_init();
key_init();
security_init();
vfs_caches_init(num_physpages);
radix_tree_init();
signals_init();
/* rootfs populating might need page-writeback */
page_writeback_init();
#ifdef CONFIG_PROC_FS
proc_root_init();
#endif
cpuset_init();
taskstats_init_early();
delayacct_init();

check_bugs();

acpi_early_init(); /* before LAPIC and SMP init */

/* Do the rest non-__init'ed, we're now alive */
rest_init();
}

分析start_kernel()源码， 其中setup_arch() 和 reset_init()是两个比较关键的函数。下面将具体分析这两个函数。
5.2. setup_arch()函数分析
首先我们来分析下setup_arch()函数。
Setup_arch()函数主要工作是安装cpu和machine，并为start_kernel()后面的初始化函数指针指定值。
其中setup_processor()函数调用linux/arch/arm/kernel/head_common.S 中的lookup_processor_type函数查询处理器的型号并安装。

Setup_machine()函数调用inux/arch/arm/kernel/head_common.S 中的lookup_machine_type(__machine_arch_type)函数根据体系结构号__machine_arch_type，在 __arch_info_begin和__arch_info_end段空间查询体系结构。问题是__machine_arch_type是在什么时候赋 的初值？__arch_info_begin和__arch_info_end段空间到底放的是什么内容？
__machine_arch_type是一个全局变量，在linux/boot/decompress/misc.c的解压缩函数中得以赋值。
decompress_kernel(ulg output_start, ulg free_mem_ptr_p, ulg free_mem_ptr_end_p, int arch_id)
{
__machine_arch_type = arch_id;
}

__arch_info_begin和__arch_info_end段空间到底放的内容由链接器决定，存放是.arch.info.init段的 内容。这个段是通过段属性__attribute__指定的。Grep一下.arch.info.init 得到./include/asm/mach/arch.h:53: __attribute__((__section__(".arch.info.init"))) = {       在linux/include/asm-arm/mach/arch.h 中发现MACHINE_START宏定义。

#define MACHINE_START(_type,_name) 
static const struct machine_desc __mach_desc_##_type 
 __attribute_used__ 
 __attribute__((__section__(".arch.info.init"))) = { 
.nr = MACH_TYPE_##_type, 
.name = _name,

#define MACHINE_END 
};

inux/arch/arm/mach-s3c2410/mach-smdk2410.c中对.arch.info.init段的初始化如下。

 MACHINE_START(SMDK2410, "SMDK2410") /* @TODO: request a new identifier and switch
    * to SMDK2410 */
/* Maintainer: Jonas Dietsche */
.phys_io = S3C2410_PA_UART,
.io_pg_offst = (((u32)S3C24XX_VA_UART) >> 18) & 0xfffc,
.boot_params = S3C2410_SDRAM_PA + 0x100,
.map_io = smdk2410_map_io,
.init_irq = s3c24xx_init_irq,
.init_machine = smdk_machine_init,
.timer = &s3c24xx_timer,
MACHINE_END

由此可见在.arch.info.init段内存放了__desc_mach_desc_SMDK2410结构体。初始化了相应的初始化函数指针。问题又来了， 这些初始化指针函数是什么时候被调用的呢？
分析发现，不一而同。
如 s3c24xx_init_irq()函数是通过start_kernel()里的init_IRQ()函数调用init_arch_irq()实现的。 因为在MACHINE_START结构体中  .init_irq = s3c24xx_init_irq，而在setup_arch()函数中init_arch_irq = mdesc->init_irq， 所以调用init_arch_irq()就相当于调用了s3c24xx_init_irq()。
又如smdk_machine_init()函数 的初始化。在MACHINE_START结构体中，函数指针赋值，.init_machine = smdk_machine_init。而init_machine()函数被linux/arch/arm/kernel/setup.c文件中的 customize_machine()函数调用并被arch_initcall(Fn)宏处 理，arch_initcall(customize_machine)。 被arch_initcall(Fn)宏处理过函数将linux/init/main.c
do_initcalls()函数调用。 具体参看下边的部分。

void __init setup_arch(char **cmdline_p)
{
struct tag *tags = (struct tag *)&init_tags;
struct machine_desc *mdesc;
char *from = default_command_line;

setup_processor();
mdesc = setup_machine(machine_arch_type);//machine_arch_type =SMDK2410  by edwin
machine_name = mdesc->name;

if (mdesc->soft_reboot)
reboot_setup("s");

if (mdesc->boot_params)
tags = phys_to_virt(mdesc->boot_params);

/*
 * If we have the old style parameters, convert them to
 * a tag list.
 */
if (tags->hdr.tag != ATAG_CORE)
convert_to_tag_list(tags);
if (tags->hdr.tag != ATAG_CORE)
tags = (struct tag *)&init_tags;

if (mdesc->fixup)
mdesc->fixup(mdesc, tags, &from, &meminfo);

if (tags->hdr.tag == ATAG_CORE) {
if (meminfo.nr_banks != 0)
squash_mem_tags(tags);
parse_tags(tags);
}

init_mm.start_code = (unsigned long) &_text;
init_mm.end_code   = (unsigned long) &_etext;
init_mm.end_data   = (unsigned long) &_edata;
init_mm.brk    = (unsigned long) &_end;

memcpy(saved_command_line, from, COMMAND_LINE_SIZE);
  
8、浅谈分析Arm linux 内核移植及系统初始化的过程  咨询QQ：313807838
 saved_command_line[COMMAND_LINE_SIZE-1] = '';
parse_cmdline(cmdline_p, from);
paging_init(&meminfo, mdesc);
request_standard_resources(&meminfo, mdesc);

#ifdef CONFIG_SMP
smp_init_cpus();
#endif

cpu_init();

/*
 * Set up various architecture-specific pointers
 */
init_arch_irq = mdesc->init_irq;
system_timer = mdesc->timer;
init_machine = mdesc->init_machine;

#ifdef CONFIG_VT
#if defined(CONFIG_VGA_CONSOLE)
conswitchp = &vga_con;
#elif defined(CONFIG_DUMMY_CONSOLE)
conswitchp = &dummy_con;
#endif
#endif
}
5.3. rest_init()函数分析
下面我们来分析下rest_init()函数。
Start_kernel() 函数负责初始化内核各子系统，最后调用reset_init()，启动一个叫做init的内核线程，继续初始化。在init内核线程中，将执行下列 init()函数的程序。Init()函数负责完成根文件系统的挂接、初始化设备驱动程序和启动用户空间的init进程等重要工作。

static void noinline rest_init(void)
__releases(kernel_lock)
{
kernel_thread(init, NULL, CLONE_FS | CLONE_SIGHAND);
numa_default_policy();
unlock_kernel();

/*
 * The boot idle thread must execute schedule()
 * at least one to get things moving:
 */
preempt_enable_no_resched();
schedule();
preempt_disable();

/* Call into cpu_idle with preempt disabled */
cpu_idle();
}

static int init(void * unused)
{
lock_kernel();
/*
 * init can run on any cpu.
 */
set_cpus_allowed(current, CPU_MASK_ALL);
/*
 * Tell the world that we're going to be the grim
 * reaper of innocent orphaned children.
 *
 * We don't want people to have to make incorrect
 * assumptions about where in the task array this
 * can be found.
 */
child_reaper = current;

smp_prepare_cpus(max_cpus);

do_pre_smp_initcalls();

smp_init();
sched_init_smp();

cpuset_init_smp();

/*
 * Do this before initcalls, because some drivers want to access
 * firmware files.
 */
populate_rootfs();   //挂接根文件系统

do_basic_setup();   //初始化设备驱动程序

/*
 * check if there is an early userspace init.  If yes, let it do all
 * the work        //启动用户空间的init进程
 
9、浅谈分析Arm linux 内核移植及系统初始化的过程 咨询QQ：313807838
  */

if (!ramdisk_execute_command)
ramdisk_execute_command = "/init";

if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
ramdisk_execute_command = NULL;
prepare_namespace();
}

/*
 * Ok, we have completed the initial bootup, and
 * we're essentially up and running. Get rid of the
 * initmem segments and start the user-mode stuff..
 */
free_initmem();
unlock_kernel();
mark_rodata_ro();
system_state = SYSTEM_RUNNING;
numa_default_policy();

if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
printk(KERN_WARNING "Warning: unable to open an initial console.n");

(void) sys_dup(0);
(void) sys_dup(0);

if (ramdisk_execute_command) {
run_init_process(ramdisk_execute_command);
printk(KERN_WARNING "Failed to execute %sn",
ramdisk_execute_command);
}

/*
 * We try each of these until one succeeds.
 *
 * The Bourne shell can be used instead of init if we are 
 * trying to recover a really broken machine.
 */
if (execute_command) {
run_init_process(execute_command);
printk(KERN_WARNING "Failed to execute %s.  Attempting "
"defaults...n", execute_command);
}
run_init_process("/sbin/init");
run_init_process("/etc/init");
run_init_process("/bin/init");
run_init_process("/bin/sh");

panic("No init found.  Try passing init= option to kernel.");
}

5.3.1. 挂接根文件系统
Linux/init/ramfs.c
void __init populate_rootfs(void)
{
char *err = unpack_to_rootfs(__initramfs_start,
 __initramfs_end - __initramfs_start, 0);
if (err)
panic(err);
#ifdef CONFIG_BLK_DEV_INITRD
if (initrd_start) {
#ifdef CONFIG_BLK_DEV_RAM
int fd;
printk(KERN_INFO "checking if image is initramfs...");
err = unpack_to_rootfs((char *)initrd_start,
initrd_end - initrd_start, 1);
if (!err) {
printk(" it isn");
unpack_to_rootfs((char *)initrd_start,
initrd_end - initrd_start, 0);
free_initrd();
return;
}
printk("it isn't (%s); looks like an initrdn", err);

 fd = sys_open("/initrd.image", O_WRONLY|O_CREAT, 0700);
if (fd >= 0) {
sys_write(fd, (char *)initrd_start,
initrd_end - initrd_start);
sys_close(fd);
free_initrd();
}
#else
printk(KERN_INFO "Unpacking initramfs...");
err = unpack_to_rootfs((char *)initrd_start,
initrd_end - initrd_start, 0);
if (err)
panic(err);
printk(" donen");
free_initrd();
#endif
}
#endif
}

5.3.2. 初始化设备5.3.3. 驱动程序
linux/init/main.c
static void __init do_basic_setup(void)
{
/* drivers will send hotplug events */
init_workqueues();
usermodehelper_init();
driver_init();   /* 初始化驱动程序模型。调用驱动初始化函数初始化子系统。 */

#ifdef CONFIG_SYSCTL
sysctl_init();
#endif

do_initcalls();
}

linux/init/main.c
extern initcall_t __initcall_start[], __initcall_end[];

static void __init do_initcalls(void)
{
initcall_t *call;
int count = preempt_count();

for (call = __initcall_start; call < __initcall_end; call++) {
char *msg = NULL;
char msgbuf[40];
int result;

if (initcall_debug) {
printk("Calling initcall 0x%p", *call);
print_fn_deor_symbol(": %s()",
(unsigned long) *call);
printk("n");
}

result = (*call)();

……
……
……
}

/* Make sure there is no pending stuff from the initcall sequence */
flush_scheduled_work();
}
分 析上面一段代码可以看出，设备的初始化是通过do_basic_setup()函数调用do_initcalls()函数，实现 __initcall_start, __initcall_end段之间的指针函数执行的。而到底是那些驱动函数怎么会被集中到这个段内的呢？我们知道系统内存空间的分配是由链接器ld读取 链接脚本文件决定。链接器将同样属性的文件组织到相同的段里面去，如所有的.text段都被放在一起。在链接脚本里面可以获得某块内存空间的具体地址。我 们来看下linux-2.6.18.8archarmkernelvmlinux.lds.S文件。由于文件过长，只贴出和 __initcall_start, __initcall_end相关的部分。
__initcall_start = .;
*(.initcall1.init)
*(.initcall2.init)
*(.initcall3.init)
*(.initcall4.init)
*(.initcall5.init)
*(.initcall6.init)
*(.initcall7.init)
__initcall_end = .;
从 脚本文件中我们可以看出， 在__initcall_start, __initcall_end之间放置的是属行为(.initcall*.init)的函数数据 。在linux/include/linux/init.h文件中可以知道，(.initcall*.init)属性是由 __define_initcall(level, fn)宏设定的。

#define __define_initcall(level,fn) 
static initcall_t __initcall_##fn __attribute_used__ 
 
11、浅谈分析Arm linux 内核移植及系统初始化的过程咨询QQ：313807838 
 __attribute__((__section__(".initcall" level ".init"))) = fn

#define core_initcall(fn) __define_initcall("1",fn)
#define postcore_initcall(fn) __define_initcall("2",fn)
#define arch_initcall(fn) __define_initcall("3",fn)
#define subsys_initcall(fn) __define_initcall("4",fn)
#define fs_initcall(fn) __define_initcall("5",fn)
#define device_initcall(fn) __define_initcall("6",fn)
#define late_initcall(fn) __define_initcall("7",fn)
#define __initcall(fn)      device_initcall(fn)

由此可以判断，所有的设备驱动函数都必然通过*_initcall(fn)宏的处理。以此为入口，可以查询所有的设备驱动。
core_initcall(fn)
static int __init consistent_init(void)        linux/arch/arm/mm/consistent.c
static int __init v6_userpage_init(void)      linux/arch/arm/mm/copypage-v6.c
static int __init init_dma(void)             linux/arch/arm/kernel/dma.c
static int __init s3c2410_core_init(void)     linux/arch/arm/mach-s3c2410/s3c2410.c

postcore_initcall(fn)
static int ecard_bus_init(void)  linux/arch/arm/kernel/ecard.c

arch_initcall(fn)
static __init int bast_irq_init(void)  linux/arch/arm/mach-s3c2410/bast-irq.c
static int __init s3c_arch_init(void)  linux/arch/arm/mach-s3c2410/cpu.c
static __init int pm_simtec_init(void)      linux/arch/arm/mach-s3c2410/pm-simtec.c
static int __init customize_machine(void)  linux/arch/arm/kernel/setup.c

subsys_initcall(fn)
static int __init ecard_init(void)  linux/arch/arm/kernel/ecard.c
int __init scoop_init(void)  linux/arch/arm/common/scoop.c
static int __init topology_init(void)  linux/arch/arm/kernel/setup.c

fs_initcall(fn)
static int __init alignment_init(void)  linux/arch/arm/mm/alignment.c

device_initcall(fn)
static int __init leds_init(void)  linux/arch/arm/kernel/time.c
static int __init timer_init_sysfs(void)  linux/arch/arm/kernel/time.c

late_initcall(fn)
static int __init crunch_init(void)  arch/arm/kernel/crunch.c
static int __init arm_mrc_hook_init(void)  linux/arch/arm/kernel/traps.c