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转载请注明来源：cuixiaolei的技术博客
这篇文章是lk启动流程分析，将会详细介绍下面的内容：
1).正常开机引导流程
2).recovery引导流程
3).fastboot引导流程
4).ffbm引导流程
5).lk向kernel传参
start----------------------------------------
在bootable/bootloader/lk/arch/arm/crt0.S文件中有下面代码，所以从kmain()开始介绍
bl kmain
kmain函数位于bootable/bootloader/lk/kernel/main.c
/* called from crt0.S */ void kmain(void) __NO_RETURN __EXTERNALLY_VISIBLE; void kmain(void) { // get us into some sort of thread context thread_init_early(); //初始化线程上下文 #ifdef FEATURE_AFTER_SALE_LOG_LK // do console early init console_init_early(); //初始化控制台 #endif // early arch stuff arch_early_init(); //架构初始化，如关闭cache，使能mmu // do any super early platform initialization platform_early_init(); //平台早期初始化 // do any super early target initialization target_early_init(); //目标设备早期初始化,初始化串口 dprintf(INFO, "welcome to lk\n\n"); bs_set_timestamp(BS_BL_START); // deal with any static constructors dprintf(SPEW, "calling constructors\n"); call_constructors(); // bring up the kernel heap dprintf(SPEW, "initializing heap\n"); heap_init(); //堆初始化 __stack_chk_guard_setup(); // initialize the threading system dprintf(SPEW, "initializing threads\n"); thread_init(); //线程初始化 #ifdef FEATURE_AFTER_SALE_LOG_LK // initialize the console layer // TCTNB Wangyongliang task1167051 dprintf(SPEW, "initializing console layer\n"); console_init(); //初始化控制台 #endif // initialize the dpc system dprintf(SPEW, "initializing dpc\n"); dpc_init(); //lk系统控制器初始化 // initialize kernel timers dprintf(SPEW, "initializing timers\n"); timer_init(); //kernel时钟初始化 #if (!ENABLE_NANDWRITE) // create a thread to complete system initialization dprintf(SPEW, "creating bootstrap completion thread\n"); thread_resume(thread_create("bootstrap2", &bootstrap2, NULL, DEFAULT_PRIORITY, DEFAULT_STACK_SIZE)); //创建一个线程初始化系统 // enable interrupts exit_critical_section(); //使能中断 // become the idle thread thread_become_idle(); //本线程切换成idle线程，idle为空闲线程，当没有更高优先级的线程时才执行 #else bootstrap_nandwrite(); #endif }
arch_early_init()负责使能内存管理单元mmu
bootable/bootloader/lk/arch/arm/arch.c void arch_early_init(void) { /* turn off the cache */ arch_disable_cache(UCACHE); //关闭cache /* set the vector base to our exception vectors so we dont need to double map at 0 */ #if ARM_CPU_CORTEX_A8 set_vector_base(MEMBASE); //设置异常向量基地址 #endif #if ARM_WITH_MMU arm_mmu_init(); //使能mmu #endif /* turn the cache back on */ arch_enable_cache(UCACHE); //打开cache #if ARM_WITH_NEON /* enable cp10 and cp11 */ uint32_t val; __asm__ volatile("mrc p15, 0, %0, c1, c0, 2" : "=r" (val)); val |= (3<<22)|(3<<20); __asm__ volatile("mcr p15, 0, %0, c1, c0, 2" :: "r" (val)); isb(); /* set enable bit in fpexc */ __asm__ volatile("mrc p10, 7, %0, c8, c0, 0" : "=r" (val)); val |= (1<<30); __asm__ volatile("mcr p10, 7, %0, c8, c0, 0" :: "r" (val)); #endif #if ARM_CPU_CORTEX_A8 /* enable the cycle count register */ uint32_t en; __asm__ volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (en)); en &= ~(1<<3); /* cycle count every cycle */ en |= 1; /* enable all performance counters */ __asm__ volatile("mcr p15, 0, %0, c9, c12, 0" :: "r" (en)); /* enable cycle counter */ en = (1<<31); __asm__ volatile("mcr p15, 0, %0, c9, c12, 1" :: "r" (en)); #endif }
platform_early_init()平台早期初始化，初始化平台的时钟和主板
bootable\bootloader\lk\platform\msm8952\platform.c
void platform_early_init(void) { board_init(); //主板初始化 platform_clock_init(); //时钟初始化 qgic_init(); qtimer_init(); }
从代码可知，会创建一个bootstrap2线程，并使能中断
static int bootstrap2(void *arg) { dprintf(SPEW, "top of bootstrap2()\n"); arch_init(); //架构初始化，此函数为空，什么都没做 // XXX put this somewhere else #if WITH_LIB_BIO bio_init(); #endif #if WITH_LIB_FS fs_init(); #endif // initialize the rest of the platform dprintf(SPEW, "initializing platform\n"); platform_init(); // 平台初始化,不同的平台要做的事情不一样，可以是初始化系统时钟,超频等 // initialize the target dprintf(SPEW, "initializing target\n"); target_init(); //目标设备初始化,主要初始化Flash,整合分区表等 dprintf(SPEW, "calling apps_init()\n"); apps_init(); //应用功能初始化，主要调用boot_init，启动kernel，加载boot/recovery镜像等 return 0; }
apps_init()通过下面方式进入aboot_init()函数
APP_START(aboot)
.init = aboot_init,
APP_END
bootable/bootloader/lk/app/app.cvoid apps_init(void) { const struct app_descriptor *app; /* call all the init routines */ for (app = &__apps_start; app != &__apps_end; app++) { if (app->init) app->init(app); } /* start any that want to start on boot */ for (app = &__apps_start; app != &__apps_end; app++) { if (app->entry && (app->flags & APP_FLAG_DONT_START_ON_BOOT) == 0) { start_app(app); } } }
从这里开始是这篇文章的重点，分析aboot.c文件。每个项目的文件可能会有不同，但是差别会很小。
bootable/bootloader/lk/app/aboot/aboot.c void aboot_init(const struct app_descriptor *app) { unsigned reboot_mode = 0; unsigned restart_reason = 0; unsigned hard_reboot_mode = 0; bool boot_into_fastboot = false; uint8_t pon_reason = pm8950_get_pon_reason(); //pm8950_get_pon_reason() 获取开机原因 /* Setup page size information for nv storage */ if (target_is_emmc_boot()) //检测是emmc还是flash存储，并设置页大小，一般是2048 { page_size = mmc_page_size(); page_mask = page_size - 1; } else { page_size = flash_page_size(); page_mask = page_size - 1; } ASSERT((MEMBASE + MEMSIZE) > MEMBASE); //断言，如果内存基地址+内存大小小于内存基地址，则直接终止错误 read_device_info(&device); //从devinfo分区表read data到device结构体 read_allow_oem_unlock(&device); //devinfo分区里记录了unlock状态，从device中读取此信息 /* Display splash screen if enabled */ if (!check_alarm_boot()) { dprintf(SPEW, "Display Init: Start\n"); target_display_init(device.display_panel); //显示splash，Splash也就是应用程序启动之前先启动一个画面,上面简单的介绍应用程序的厂商,厂商的LOGO,名称和版本等信息,多为一张图片 dprintf(SPEW, "Display Init: Done\n"); } #ifdef FEATURE_LOW_POWER_DISP_LK if(is_low_voltage) { //如果电量低，则显示关机动画，并关闭设备 mdelay(2000); //target_uninit(); target_display_shutdown(); shutdown_device(); } #endif is_alarm_boot = check_alarm_boot(); //检测开机原因是否是由于关机闹钟导致 target_serialno((unsigned char *) sn_buf); dprintf(SPEW,"serial number: %s\n",sn_buf); memset(display_panel_buf, ‘\0‘, MAX_PANEL_BUF_SIZE); /* * Check power off reason if user force reset, * if yes phone will do normal boot. */ if (is_user_force_reset()) //如果强制重启，直接进入normal_boot goto normal_boot; dprintf(ALWAYS, "pon_reason=0x%02x\n", pon_reason); /* Check if we should do something other than booting up */ if ( (pon_reason & USB_CHG) //启动原因是插上USB，并且用户同时按住了音量上下键，进入下载模式 && (keys_get_state(KEY_VOLUMEUP) && keys_get_state(KEY_VOLUMEDOWN))) { display_dloadimage_on_screen(); //显示下载模式图片 volume_keys_init(); //初始化音量按键 int i = 0; int j = 0; int k = 0; dload_flag = 1 ; while(1) //进入下载模式后，通过不同的按键组合进入不同的模式，下面的代码逻辑很简单，就不介绍了 { thread_sleep(200); //dprintf(ALWAYS, "in while circle\n"); if ( check_volume_up_key() && !check_volume_down_key() && !check_power_key() ) { /* Hold volume_up_key 3 sec to download mode, if not enough, need to hold another 3 sec. */ for(i = 0;i < 15;++i) { thread_sleep(200); if (!check_volume_up_key()) { dprintf(ALWAYS, "press volume_up not enough time\n"); break; } } if(i == 15) { break; } } else if (check_power_key() && !check_volume_up_key() && !check_volume_down_key()) { /* Hold power_key 1 sec to normal boot, if not enough, need to hold another 1 sec. */ for(j = 0;j < 5;++j) { thread_sleep(200); if (!check_power_key()) { //dprintf(ALWAYS, "press power_key not enough time\n"); break; } } if(j == 5) { goto normal_boot; } } else if (!check_volume_down_key() && !check_volume_up_key() && !check_power_key()) { /* Hold no key and go to normal boot 30 sec later. */ for(k = 0;k < 150;++k) { thread_sleep(200); if (check_power_key() || check_volume_up_key()) { //dprintf(ALWAYS, "press nothing\n"); break; } } if(k == 150) { //dprintf(ALWAYS, "goto normal_boot\n"); goto normal_boot; } } } dprintf(CRITICAL,"dload mode key sequence detected\n"); if (set_download_mode(EMERGENCY_DLOAD)) { dprintf(CRITICAL,"dload mode not supported by target\n"); } else { reboot_device(DLOAD); dprintf(ALWAYS,"Failed to reboot into dload mode\n"); } boot_into_fastboot = true; //下载模式本质上是进入fastboot }
if (!boot_into_fastboot) //如果不是通过usb+上下键进入下载模式 { if (keys_get_state(KEY_HOME) || (keys_get_state(KEY_VOLUMEUP) && !keys_get_state(KEY_VOLUMEDOWN))) //上键+电源键 进入recovery模式 { boot_into_recovery = 1; struct recovery_message msg; strcpy(msg.recovery, "recovery\n--show_text"); } if (!boot_into_recovery && (keys_get_state(KEY_BACK) || (keys_get_state(KEY_VOLUMEDOWN) && !keys_get_state(KEY_VOLUMEUP)))) //下键+back键进入fastboot模式，我的手机是有back实体键的 boot_into_fastboot = true; } reboot_mode = check_reboot_mode(); //检测开机原因，并且修改相应的标志位 hard_reboot_mode = check_hard_reboot_mode(); if (reboot_mode == RECOVERY_MODE || hard_reboot_mode == RECOVERY_HARD_RESET_MODE) { boot_into_recovery = 1; } else if(reboot_mode == FASTBOOT_MODE || hard_reboot_mode == FASTBOOT_HARD_RESET_MODE) { boot_into_fastboot = true; } else if(reboot_mode == ALARM_BOOT || hard_reboot_mode == RTC_HARD_RESET_MODE) { boot_reason_alarm = true; } else if (reboot_mode == DM_VERITY_ENFORCING) { device.verity_mode = 1; write_device_info(&device); } else if(reboot_mode == DM_VERITY_LOGGING) { device.verity_mode = 0; write_device_info(&device); } else if(reboot_mode == DM_VERITY_KEYSCLEAR) { if(send_delete_keys_to_tz()) ASSERT(0); } normal_boot: if(dload_flag){ display_image_on_screen(); //显示界面，上面提到过 } if (!boot_into_fastboot) //如果不是fastboot模式 { if (target_is_emmc_boot()) { if(emmc_recovery_init()) dprintf(ALWAYS,"error in emmc_recovery_init\n"); if(target_use_signed_kernel()) { if((device.is_unlocked) || (device.is_tampered)) { #ifdef TZ_TAMPER_FUSE set_tamper_fuse_cmd(); #endif #if USE_PCOM_SECBOOT set_tamper_flag(device.is_tampered); #endif } } boot_linux_from_mmc(); //程序会跑到这里，又一个重点内容，下面会独立分析这个函数。 } else { recovery_init(); #if USE_PCOM_SECBOOT if((device.is_unlocked) || (device.is_tampered)) set_tamper_flag(device.is_tampered); #endif boot_linux_from_flash(); } dprintf(CRITICAL, "ERROR: Could not do normal boot. Reverting " "to fastboot mode.\n"); } /* We are here means regular boot did not happen. Start fastboot. */ /* register aboot specific fastboot commands */ aboot_fastboot_register_commands(); //注册fastboot命令，建议看下此函数的源码，此函数是fastboot支持的命令，如flash、erase等等 /* dump partition table for debug info */ partition_dump(); /* initialize and start fastboot */ fastboot_init(target_get_scratch_address(), target_get_max_flash_size()); //初始化fastboot #if FBCON_DISPLAY_MSG display_fastboot_menu_thread(); //显示fastboot界面 #endif }
关于device_info,这里多说一点
devinfo Device information including:iis_unlocked, is_tampered, is_verified, charger_screen_enabled, display_panel, bootloader_version, radio_version All these attirbutes are set based on some specific conditions and written on devinfo partition.
devinfo是一个独立的分区，里面存放了下面的一些信息，上面是高通对这个分区的介绍。
struct device_info { unsigned char magic[DEVICE_MAGIC_SIZE]; bool is_unlocked; bool is_tampered; bool is_verified; bool charger_screen_enabled; char display_panel[MAX_PANEL_ID_LEN]; char bootloader_version[MAX_VERSION_LEN]; char radio_version[MAX_VERSION_LEN]; };
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原文地址：http://www.cnblogs.com/xiaolei-kaiyuan/p/5458145.html
