高通平台dts的匹配过程分析

在arch/arm/mach-msm/board-8909.c中：

DT_MACHINE_START(MSM8909_DT,

"Qualcomm Technologies, Inc. MSM 8909 (Flattened Device Tree)")

.map_io = msm8909_map_io,

.init_machine = msm8909_init,

.dt_compat = msm8909_dt_match,

.reserve = msm8909_dt_reserve,

.smp = &msm8916_smp_ops,

MACHINE_END

经过宏替换，最终变为:

static const struct machine_desc __mach_desc_MSM8909_DT __used __attribute__((__section__(".arch.info.init"))) = {

.nr = ~0,

.name = "Qualcomm Technologies, Inc. MSM 8909 (Flattened Device Tree)",

.map_io = msm8909_map_io,

.init_machine = msm8909_init,

.dt_compat = msm8909_dt_match,

.reserve = msm8909_dt_reserve,

.smp = &msm8916_smp_ops,

}

msm8909_dt_match定义如下：

static const char *msm8909_dt_match[] __initconst = {

"qcom,msm8909",

"qcom,apq8009",

NULL

};

编译器会将machine_desc放在一个叫.arch.info.init的段中，具体可以参考arch/arm/kernel/vmlinux.lds.S文件：

.init.arch.info : {

__arch_info_begin = .;

*(.arch.info.init)

__arch_info_end = .;

}

另外在高通的dts文件中，会定义compatible = "qcom,msm8909-qrd", "qcom,msm8909", "qcom,qrd";通过"qcom,msm8909"匹配，具体过程如下：

在arch/arm/kernel/setup.c中，setup_arch会调用setup_machine_fdt(__atags_pointer)来匹配machine：

const struct machine_desc * __init setup_machine_fdt(unsigned int dt_phys)

{

//删除了部分代码

for_each_machine_desc(mdesc) {

score = of_flat_dt_match(dt_root, mdesc->dt_compat);

if (score > 0 && score < mdesc_score) {

mdesc_best = mdesc;

mdesc_score = score;

}

}

//删除了部分代码

return mdesc_best;

}

for_each_machine_desc宏展开如下：

#define for_each_machine_desc(p) \

for (p = __arch_info_begin; p < __arch_info_end; p++)

由此可见，在.arch.info.init段中，依次取出每个machine描述符，根据dt_compat属性来匹配dts，对应msm8909来说就是"qcom,msm8909"。

__atags_pointer是指向dts的指针，它的值在arch/arm/kernel/head-common.S文件中被赋值：

__mmap_switched:

adr r3, __mmap_switched_data

ldmia r3!, {r4, r5, r6, r7}

cmp r4, r5 @ Copy data segment if needed

1: cmpne r5, r6

ldrne fp, [r4], #4

strne fp, [r5], #4

bne 1b

mov fp, #0 @ Clear BSS (and zero fp)

1: cmp r6, r7

strcc fp, [r6],#4

bcc 1b

ARM( ldmia r3, {r4, r5, r6, r7, sp})

THUMB( ldmia r3, {r4, r5, r6, r7} )

THUMB( ldr sp, [r3, #16] )

str r9, [r4] @ Save processor ID

str r1, [r5] @ Save machine type

str r2, [r6] @ Save atags pointer

cmp r7, #0

bicne r4, r0, #CR_A @ Clear 'A' bit

stmneia r7, {r0, r4} @ Save control register values

b start_kernel

ENDPROC(__mmap_switched)

.align 2

.type __mmap_switched_data, %object

__mmap_switched_data:

.long __data_loc @ r4

.long _sdata @ r5

.long __bss_start @ r6

.long _end @ r7

.long processor_id @ r4

.long __machine_arch_type @ r5

.long __atags_pointer @ r6

#ifdef CONFIG_CPU_CP15

.long cr_alignment @ r7

#else

.long 0 @ r7

#endif

.long init_thread_union + THREAD_START_SP @ sp

.size __mmap_switched_data, . - __mmap_switched_data