高通平台dtb文件的加载过程「建议收藏」

2022-11-17 16:27:18 浏览数 (1)

高通平台dtb文件的加载过程

  • 高通平台对dts的两种打包方式
    • zImage-dtb
    • dt.img
  • zImage-dtb方式
    • zImage-dtb的编译
    • 二进制文件查看
    • lk的加载过程代码分析
  • dt.img方式
    • dt.img的编译
    • dt.img的构造
    • lk的加载过程代码分析
  • 小结

高通平台对dts的两种打包方式

zImage-dtb

直接和kernel编译在一起，生成zImage-dtb，dtb的位置在kernel起始地址偏移0x2C的位置，然后和kernel一起打包到bootimage里。

dt.img

独立编译出dt.img, 然后打包到bootimage里。

zImage-dtb方式

zImage-dtb的编译

dtb怎么编译进bootimage的？ makefile文件分析

.config 文件里生成的内容如下

代码语言：javascript复制
CONFIG_ARCH_MSM8916=y

CONFIG_ARCH_MSM8937=y

CONFIG_ARCH_MSM8917=y

CONFIG_ARCH_MSM8920=y

CONFIG_ARCH_MSM8940=y

CONFIG_ARCH_MSM8953=y

Jetbrains全家桶1年46，售后保障稳定

kernel/msm-3.18/arch/arm/boot/dts/qcom/Makefile

（只要这些arch定义了 这些dtb文件都会被包含进去）

代码语言：javascript复制
dtb-$(CONFIG_ARCH_MDMCALIFORNIUM)  = mdmcalifornium-sim.dtb 

mdmcalifornium-rumi.dtb

…

代码语言：javascript复制
mdmcalifornium-v1.1-nand-mtp.dtb 

mdmcalifornium-v1.1-nand-dualwifi-mtp.dtb



dtb-$(CONFIG_ARCH_MSM8937)  = msm8937-rumi.dtb 

msm8937-pmi8950-cdp.dtb 

.......

apq8037-pmi8950-mtp.dtb 

apq8037-pmi8937-mtp.dtb



dtb-$(CONFIG_ARCH_MSM8917)  = msm8917-rumi.dtb 

apq8017-pmi8937-cdp.dtb

…

代码语言：javascript复制
msm8917-qgp-tmo.dtb 

msm8917-pmi8937-qrd-sku5.dtb

.config 文件里生成的内容如下

代码语言：javascript复制
CONFIG_USE_OF=y

CONFIG_ATAGS=y

# CONFIG_DEPRECATED_PARAM_STRUCT is not set

CONFIG_BUILD_ARM_APPENDED_DTB_IMAGE=y

CONFIG_BUILD_ARM_APPENDED_DTB_IMAGE_NAMES=

kernel/msm-3.18/arch/arm/boot/Makefile

代码语言：javascript复制
DTB_NAMES := $(subst $",,$(CONFIG_BUILD_ARM_APPENDED_DTB_IMAGE_NAMES))

ifneq ($(DTB_NAMES),)

DTB_LIST := $(addsuffix .dtb,$(DTB_NAMES))

else

DTB_LIST := $(dtb-y)

endif

DTB_OBJS := $(addprefix $(obj)/dts/qcom/,$(DTB_LIST))

因为CONFIG_BUILD_ARM_APPENDED_DTB_IMAGE_NAMES 这个为空，

所以

代码语言：javascript复制
DTB_LIST := $(dtb-y)

DTB_OBJS := $(obj)/dts/qcom/$(dtb-y)

需要编译zImage-dtb

代码语言：javascript复制
# Default target when executing plain make

ifeq ($(CONFIG_XIP_KERNEL),y)
KBUILD_IMAGE := xipImage

else ifeq ($(CONFIG_BUILD_ARM_APPENDED_DTB_IMAGE),y)

KBUILD_IMAGE := zImage-dtb

else

KBUILD_IMAGE := zImage

endif



$(obj)/Image: vmlinux FORCE

$(call if_changed,objcopy)

@$(kecho) ' Kernel: $@ is ready'



$(obj)/compressed/vmlinux: $(obj)/Image FORCE

$(Q)$(MAKE) $(build)=$(obj)/compressed $@



$(obj)/zImage: $(obj)/compressed/vmlinux FORCE

$(call if_changed,objcopy)

@$(kecho) ' Kernel: $@ is ready'



$(obj)/zImage-dtb: $(obj)/zImage $(DTB_OBJS) FORCE

$(call if_changed,cat)

@echo ' Kernel: $@ is ready'

可以看出zImage-dtb 依赖于 (obj)/zImage (DTB_OBJS)

代码语言：javascript复制
%.dtb: | scripts

$(Q)$(MAKE) $(build)=$(boot)/dts MACHINE=$(MACHINE) $(boot)/dts/$@



dtbs: scripts

$(Q)$(MAKE) $(build)=$(boot)/dts MACHINE=$(MACHINE) dtbs

$(foreach DIR, $(DTSSUBDIR), $(Q)$(MAKE) $(build)=$(boot)/dts/$(DIR) MACHINE=$(MACHINE) dtbs)



zImage-dtb: vmlinux scripts dtbs

$(Q)$(MAKE) $(build)=$(boot) MACHINE=$(MACHINE) DTSSUBDIR=$(DTSSUBDIR) $(boot)/$@

二进制文件查看

查看kernel的二进制文件，查看0x2C位置的值，此处存放的值是第一个dtb文件的偏移地址

从图中可以看出dtb所在的地址为0x008e7db0 0x800 = 0x008e85b0

0x008e85b0地址可以看到magic 0xd00dfeed(大端)

0x008e85b0 0x0002bef5 = 0x009144A5为下一个dtb的起始地址

0x009144A5地址可以看到新的dtb开始，看到magic 0xd00dfeed(大端)

lk的加载过程代码分析

appabootaboot.c

boot_linux_from_mmc dt_size = hdr->dt_size; if(dt_size) { … }else{ dtb = dev_tree_appended() }

代码语言：javascript复制
void *dev_tree_appended(void *kernel, uint32_t kernel_size, uint32_t dtb_offset, void *tags)
{ 

if (dtb_offset)
app_dtb_offset = dtb_offset;
else
memcpy((void*) &app_dtb_offset, (void*) (kernel   DTB_OFFSET), sizeof(uint32_t));	
....
while (((uintptr_t)dtb   sizeof(struct fdt_header)) < (uintptr_t)kernel_end) { 

struct fdt_header dtb_hdr;
uint32_t dtb_size;
/* the DTB could be unaligned, so extract the header, * and operate on it separately */
memcpy(&dtb_hdr, dtb, sizeof(struct fdt_header));
if (fdt_check_header((const void *)&dtb_hdr) != 0 ||
fdt_check_header_ext((const void *)&dtb_hdr) != 0 ||
((uintptr_t)dtb   (uintptr_t)fdt_totalsize((const void *)&dtb_hdr) < (uintptr_t)dtb) ||
((uintptr_t)dtb   (uintptr_t)fdt_totalsize((const void *)&dtb_hdr) > (uintptr_t)kernel_end))
break;
dtb_size = fdt_totalsize(&dtb_hdr);
dev_tree_compatible(dtb, dtb_size, dt_entry_queue);
/* goto the next device tree if any */
dtb  = dtb_size;
}
best_match_dt_entry = platform_dt_match_best(dt_entry_queue);
if (best_match_dt_entry){ 

bestmatch_tag = (void *)best_match_dt_entry->offset;
bestmatch_tag_size = best_match_dt_entry->size;
dprintf(INFO, "Best match DTB tags %u/x/0xx/%x/%x/%x/%x/%x/%x/%xn",
best_match_dt_entry->platform_id, best_match_dt_entry->variant_id,
best_match_dt_entry->board_hw_subtype, best_match_dt_entry->soc_rev,
best_match_dt_entry->pmic_rev[0], best_match_dt_entry->pmic_rev[1],
best_match_dt_entry->pmic_rev[2], best_match_dt_entry->pmic_rev[3],
best_match_dt_entry->offset, best_match_dt_entry->size);
dprintf(INFO, "Using pmic info 0x%0x/0x%x/0x%x/0x%0x for device 0x%0x/0x%x/0x%x/0x%0xn",
best_match_dt_entry->pmic_rev[0], best_match_dt_entry->pmic_rev[1],
best_match_dt_entry->pmic_rev[2], best_match_dt_entry->pmic_rev[3],
board_pmic_target(0), board_pmic_target(1),
board_pmic_target(2), board_pmic_target(3));
}
.......................
return NULL;
}

其中DTB_OFFSET的定义为0x2C，与上一节的图相对应。 根据偏移值找到dtb的位置，然后对每个dtb进行解析，找到最匹配的那个dtb，这个是有dev_tree_compatible(dtb, dtb_size, dt_entry_queue);函数来实现的。

dev_tree_compatible(void *dtb, uint32_t dtb_size, struct dt_entry_node *dtb_list) platform_dt_absolute_match(cur_dt_entry, dtb_list)

dev_tree_compatible会调用platform_dt_absolute_match来判断

代码语言：javascript复制
static int platform_dt_absolute_match(struct dt_entry *cur_dt_entry, struct dt_entry_node *dt_list)
{ 

uint32_t cur_dt_hlos_ddr;
uint32_t cur_dt_hw_platform;
uint32_t cur_dt_hw_subtype;
uint32_t cur_dt_msm_id;
dt_node *dt_node_tmp = NULL;
/* Platform-id * bit no |31 24|23 16|15 0| * |reserved|foundry-id|msm-id| */
cur_dt_msm_id = (cur_dt_entry->platform_id & 0x0000ffff);
cur_dt_hw_platform = (cur_dt_entry->variant_id & 0x000000ff);
cur_dt_hw_subtype = (cur_dt_entry->board_hw_subtype & 0xff);
/* Determine the bits 10:8 to check the DT with the DDR Size */
cur_dt_hlos_ddr = (cur_dt_entry->board_hw_subtype & 0x700);
/* 1. must match the msm_id, platform_hw_id, platform_subtype and DDR size * soc, board major/minor, pmic major/minor must less than board info * 2. find the matched DTB then return 1 * 3. otherwise return 0 */
if((cur_dt_msm_id == (board_platform_id() & 0x0000ffff)) &&
(cur_dt_hw_platform == board_hardware_id()) &&
(cur_dt_hw_subtype == board_hardware_subtype()) &&
(cur_dt_hlos_ddr == (target_get_hlos_subtype() & 0x700)) &&
(cur_dt_entry->soc_rev <= board_soc_version()) &&
((cur_dt_entry->variant_id & 0x00ffff00) <= (board_target_id() & 0x00ffff00)) &&
((cur_dt_entry->pmic_rev[0] & 0x00ffff00) <= (board_pmic_target(0) & 0x00ffff00)) &&
((cur_dt_entry->pmic_rev[1] & 0x00ffff00) <= (board_pmic_target(1) & 0x00ffff00)) &&
((cur_dt_entry->pmic_rev[2] & 0x00ffff00) <= (board_pmic_target(2) & 0x00ffff00)) &&
((cur_dt_entry->pmic_rev[3] & 0x00ffff00) <= (board_pmic_target(3) & 0x00ffff00))) { 

dt_node_tmp = dt_entry_list_init();
memcpy((char*)dt_node_tmp->dt_entry_m,(char*)cur_dt_entry, sizeof(struct dt_entry));
dprintf(SPEW, "Add DTB entry %u/x/0xx/%x/%x/%x/%x/%x/%x/%xn",
dt_node_tmp->dt_entry_m->platform_id, dt_node_tmp->dt_entry_m->variant_id,
dt_node_tmp->dt_entry_m->board_hw_subtype, dt_node_tmp->dt_entry_m->soc_rev,
dt_node_tmp->dt_entry_m->pmic_rev[0], dt_node_tmp->dt_entry_m->pmic_rev[1],
dt_node_tmp->dt_entry_m->pmic_rev[2], dt_node_tmp->dt_entry_m->pmic_rev[3],
dt_node_tmp->dt_entry_m->offset, dt_node_tmp->dt_entry_m->size);
insert_dt_entry_in_queue(dt_list, dt_node_tmp);
return 1;
}
return 0;
}

board_platform_id() board_hardware_id() board_hardware_subtype() target_get_hlos_subtype() board_soc_version()board_target_id() 几乎都来自board结构体

代码语言：javascript复制
struct board_data {
uint32_t platform;  //board_platform_id
uint32_t foundry_id;
uint32_t chip_serial;
uint32_t platform_version;//board_soc_version
uint32_t platform_hw;//board_hardware_id()
uint32_t platform_subtype;//board_hardware_subtype
uint32_t target;//board_target_id()
uint32_t baseband;
struct board_pmic_data pmic_info[MAX_PMIC_DEVICES];
uint32_t platform_hlos_subtype;//target_get_hlos_subtype即board_hlos_subtype
uint32_t num_pmics;
uint32_t pmic_array_offset;
struct board_pmic_data *pmic_info_array;
};

board在platformmsm_sharedboard.c 文件里赋值 board_init() platform_detect()

代码语言：javascript复制
			board.platform = board_info_v11.board_info_v3.msm_id;
board.platform_version = board_info_v11.board_info_v3.msm_version;
board.platform_hw = board_info_v11.board_info_v3.hw_platform;
board.platform_subtype = board_info_v11.platform_subtype;
/* * fill in board.target with variant_id information * bit no |31 24 |23 16|15 8|7 0| * board.target = |subtype|plat_hw_ver major|plat_hw_ver minor|hw_platform| * */
board.target = (((board_info_v11.platform_subtype & 0xff) << 24) |
(((board_info_v11.platform_version >> 16) & 0xff) << 16) |
((board_info_v11.platform_version & 0xff) << 8) |
(board_info_v11.board_info_v3.hw_platform & 0xff));
board.foundry_id = board_info_v11.foundry_id;
board.chip_serial = board_info_v11.chip_serial;
board.num_pmics = board_info_v11.num_pmics;
board.pmic_array_offset = board_info_v11.pmic_array_offset;
}
/* HLOS subtype * bit no |31 20 | 19 16|15 13 |12 11 | 10 8 | 7 0| * board.platform_hlos_subtype = |reserved | Boot device |Reserved | Panel | DDR detection | subtype| * | bits | | bits | Detection | */
board.platform_hlos_subtype = (board_get_ddr_subtype() << 8) | (platform_get_boot_dev() << 16) | (platform_detect_panel() << 11);

根据代码里给的注释，从smem里获得

platform_dt_absolute_match过程

代码语言：javascript复制
static int platform_dt_absolute_match(struct dt_entry *cur_dt_entry, struct dt_entry_node *dt_list)
{ 

/* Platform-id * bit no |31 24|23 16|15 0| * |reserved|foundry-id|msm-id| */
cur_dt_msm_id = (cur_dt_entry->platform_id & 0x0000ffff);
cur_dt_hw_platform = (cur_dt_entry->variant_id & 0x000000ff);
cur_dt_hw_subtype = (cur_dt_entry->board_hw_subtype & 0xff);
/* Determine the bits 10:8 to check the DT with the DDR Size */
cur_dt_hlos_ddr = (cur_dt_entry->board_hw_subtype & 0x700);
/* 1. must match the msm_id, platform_hw_id, platform_subtype and DDR size * soc, board major/minor, pmic major/minor must less than board info * 2. find the matched DTB then return 1 * 3. otherwise return 0 */
if((cur_dt_msm_id == (board_platform_id() & 0x0000ffff)) &&
(cur_dt_hw_platform == board_hardware_id()) &&
(cur_dt_hw_subtype == board_hardware_subtype()) &&
(cur_dt_hlos_ddr == (target_get_hlos_subtype() & 0x700)) &&
(cur_dt_entry->soc_rev <= board_soc_version()) &&
((cur_dt_entry->variant_id & 0x00ffff00) <= (board_target_id() & 0x00ffff00)) &&
((cur_dt_entry->pmic_rev[0] & 0x00ffff00) <= (board_pmic_target(0) & 0x00ffff00)) &&
((cur_dt_entry->pmic_rev[1] & 0x00ffff00) <= (board_pmic_target(1) & 0x00ffff00)) &&
((cur_dt_entry->pmic_rev[2] & 0x00ffff00) <= (board_pmic_target(2) & 0x00ffff00)) &&
((cur_dt_entry->pmic_rev[3] & 0x00ffff00) <= (board_pmic_target(3) & 0x00ffff00))) { 

dt_node_tmp = dt_entry_list_init();
memcpy((char*)dt_node_tmp->dt_entry_m,(char*)cur_dt_entry, sizeof(struct dt_entry));
... ...
}

对比之前需要从dts里将信息提取出来，主要是通过读取三个属性值然后提取

代码语言：javascript复制
pmic_prop = (const char *)fdt_getprop(dtb, root_offset, "qcom,pmic-id", &len_pmic_id);
board_prop = (const char *)fdt_getprop(dtb, root_offset, "qcom,board-id", &len_board_id);

plat_prop = (const char *)fdt_getprop(dtb, root_offset, “qcom,msm-id”, &len_plat_id);

代码语言：javascript复制
		board_data[i].variant_id = fdt32_to_cpu(((struct board_id *)board_prop)->variant_id);
board_data[i].platform_subtype = fdt32_to_cpu(((struct board_id *)board_prop)->platform_subtype);
dt_entry_array[k].board_hw_subtype = board_data[j].platform_subtype;
platform_data[i].platform_id = fdt32_to_cpu(((struct plat_id *)plat_prop)->platform_id);
platform_data[i].soc_rev = fdt32_to_cpu(((struct plat_id *)plat_prop)->soc_rev);
pmic_data[i].pmic_version[0]= fdt32_to_cpu(((struct pmic_id *)pmic_prop)->pmic_version[0]);
pmic_data[i].pmic_version[1]= fdt32_to_cpu(((struct pmic_id *)pmic_prop)->pmic_version[1]);
pmic_data[i].pmic_version[2]= fdt32_to_cpu(((struct pmic_id *)pmic_prop)->pmic_version[2]);
pmic_data[i].pmic_version[3]= fdt32_to_cpu(((struct pmic_id *)pmic_prop)->pmic_version[3]);

must match the msm_id, platform_hw_id, platform_subtype and DDR size 可见 msm_id, platform_hw_platform, platform_subtype and DDR size 这几个需要完全匹配才可以 cur_dt_msm_id = (cur_dt_entry->platform_id & 0x0000ffff); 来自”qcom,msm-id”

platform_hw_platform = (cur_dt_entry->variant_id & 0x000000ff); 来自 “qcom,board-id”

cur_dt_hw_subtype = (cur_dt_entry->board_hw_subtype & 0xff); 同样来自 “qcom,board-id”

总之，最终会找到一个最合适的dtb，也有可能因为配置不对找不到匹配的dtb文件。

由此可见，在dtb未匹配时，需要修改sbl里的id，或者同步修改dts里的board id，让两者匹配才可以。

dt.img方式

dt.img的编译

deviceqcomcommongenerate_extra_images.mk

代码语言：javascript复制
#----------------------------------------------------------------------
# Generate device tree image (dt.img)
#----------------------------------------------------------------------
ifneq ($(strip $(TARGET_NO_KERNEL)),true)
ifeq ($(strip $(BOARD_KERNEL_SEPARATED_DT)),true)
ifeq ($(strip $(BUILD_TINY_ANDROID)),true)
include device/qcom/common/dtbtool/Android.mk
endif
DTBTOOL := $(HOST_OUT_EXECUTABLES)/dtbTool$(HOST_EXECUTABLE_SUFFIX)
INSTALLED_DTIMAGE_TARGET := $(PRODUCT_OUT)/dt.img
possible_dtb_dirs = $(KERNEL_OUT)/arch/$(TARGET_KERNEL_ARCH)/boot/dts/ $(KERNEL_OUT)/arch/arm/boot/dts/ $(KERNEL_OUT)/arch/arm/boot/
dtb_dir = $(firstword $(wildcard $(possible_dtb_dirs)))
define build-dtimage-target
$(call pretty,"Target dt image: $(INSTALLED_DTIMAGE_TARGET)")
$(hide) $(DTBTOOL) -o $@ -s $(BOARD_KERNEL_PAGESIZE) -p $(KERNEL_OUT)/scripts/dtc/ $(dtb_dir)
$(hide) chmod a r $@
endef
$(INSTALLED_DTIMAGE_TARGET): $(DTBTOOL) $(INSTALLED_KERNEL_TARGET)
$(build-dtimage-target)
ALL_DEFAULT_INSTALLED_MODULES  = $(INSTALLED_DTIMAGE_TARGET)
ALL_MODULES.$(LOCAL_MODULE).INSTALLED  = $(INSTALLED_DTIMAGE_TARGET)
endif
endif

可见是使用dtbtool dtbtool代码定义在deviceqcomcommondtbtooldtbtool.c, 与这个文件同一目录下的dtbtool.txt是对dtbtool的使用说明。

1.1) Android boot image Header:

  1. Magic (8B)
  2. kernel size (4B)
  3. kernel addr (4B)
  4. ramdisk size (4B)
  5. ramdisk addr (4B)
  6. 2ndary size (4B)
  7. 2ndary addr (4B)
  8. tags addr (4B)
  9. page size (4B)
  10. unused #1 (4B) (zero in standard Android)
  11. unused #2 (4B) (zero in standard Android)
  12. product name (16B)
  13. kernel cmdline (512B)
  14. id (8B)

1.2) Layout: A) header (as above – 1 page) B) kernel (n pages) C) ramdisk (m pages) D) second stage (o pages) 2) QC table of device tree

dt.img的构造

可以看出magic是QCDT，version是3，num_entries是0x89

可以看出offset是0x1800, size是0x26800 （0x1800 0x26800=0x28000）

0x28000是另一个dtb的开始

lk的加载过程代码分析

代码语言：javascript复制
int boot_linux_from_mmc(void)
{ 

...............
if(dt_size) { 

dt_table_offset = ((uint32_t)image_addr   page_size   kernel_actual   ramdisk_actual   second_actual);
table = (struct dt_table*) dt_table_offset;
if (dev_tree_validate(table, hdr->page_size, &dt_hdr_size) != 0) { 

dprintf(CRITICAL, "ERROR: Cannot validate Device Tree Table n");
return -1;
}
/* Its Error if, dt_hdr_size (table->num_entries * dt_entry size   Dev_Tree Header) goes beyound hdr->dt_size*/
if (dt_hdr_size > ROUND_TO_PAGE(dt_size,hdr->page_size)) { 

dprintf(CRITICAL, "ERROR: Invalid Device Tree size n");
return -1;
}
/* Find index of device tree within device tree table */
if(dev_tree_get_entry_info(table, &dt_entry) != 0){ 

dprintf(CRITICAL, "ERROR: Getting device tree address failedn");
return -1;
}
if(dt_entry.offset > (UINT_MAX - dt_entry.size)) { 

dprintf(CRITICAL, "ERROR: Device tree contents are Invalidn");
return -1;
}
/* Ensure we are not overshooting dt_size with the dt_entry selected */
if ((dt_entry.offset   dt_entry.size) > dt_size) { 

dprintf(CRITICAL, "ERROR: Device tree contents are Invalidn");
return -1;
}
if (is_gzip_package((unsigned char *)dt_table_offset   dt_entry.offset, dt_entry.size))
{ 

unsigned int compressed_size = 0;
out_addr  = out_len;
out_avai_len -= out_len;
dprintf(INFO, "decompressing dtb: startn");
rc = decompress((unsigned char *)dt_table_offset   dt_entry.offset,
dt_entry.size, out_addr, out_avai_len,
&compressed_size, &dtb_size);
if (rc)
{ 

dprintf(CRITICAL, "decompressing dtb failed!!!n");
ASSERT(0);
}
dprintf(INFO, "decompressing dtb: donen");
best_match_dt_addr = out_addr;
} else { 

best_match_dt_addr = (unsigned char *)dt_table_offset   dt_entry.offset;
dtb_size = dt_entry.size;
}
/* Validate and Read device device tree in the tags_addr */
if (check_aboot_addr_range_overlap(hdr->tags_addr, dtb_size) ||
check_ddr_addr_range_bound(hdr->tags_addr, dtb_size))
{ 

dprintf(CRITICAL, "Device tree addresses are not validn");
return -1;
}
memmove((void *)hdr->tags_addr, (char *)best_match_dt_addr, dtb_size);
} else { 

/* Validate the tags_addr */
if (check_aboot_addr_range_overlap(hdr->tags_addr, kernel_actual) ||
check_ddr_addr_range_bound(hdr->tags_addr, kernel_actual))
{ 

dprintf(CRITICAL, "Device tree addresses are not valid.n");
return -1;
}
/* * If appended dev tree is found, update the atags with * memory address to the DTB appended location on RAM. * Else update with the atags address in the kernel header */
void *dtb;
dtb = dev_tree_appended(
(void*)(image_addr   page_size  
patched_kernel_hdr_size),
hdr->kernel_size, dtb_offset,
(void *)hdr->tags_addr);
if (!dtb) { 

dprintf(CRITICAL, "ERROR: Appended Device Tree Blob not foundn");
return -1;
}
} 
....................
}

在这种情况下dt_size是非0的，走第一个分支，第二个分支是zImage-dtb那种方式使用的

代码语言：javascript复制
int dev_tree_get_entry_info(struct dt_table *table, struct dt_entry *dt_entry_info)
for(i = 0; found == 0 && i < table->num_entries; i  )
platform_dt_absolute_match(cur_dt_entry, dt_entry_queue);
best_match_dt_entry = platform_dt_match_best(dt_entry_queue);

调用关系如上，对每一个dt_entry调用platform_dt_absolute_match，找到最匹配的，匹配方法与zImage-dtb方式类似，不再赘述。

小结

device tree最终编译成dtb文件，而高通平台为了让一个bootimage支持多种不同的配置（甚至是不同的board，不同的平台），将众多的dtb文件一起同时编译和打包。为了区分匹配不同的平台，高通平台需要再sbl里配置id，与device tree里的qcom,pmic-id和qcom,board-id相呼应，这两者需要匹配，才能实现dtb文件的正确加载，然后由lk传递给kernel。而dtb的识别是在lk里实现的，lk代码里对dt.img方式和zImage-dtb方式做了兼容，可以同时识别这两种方式。

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android kernel 打包

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