[Zedboard Linux系统移植]-从MACHINE_START开始

) /* 64KB way size, 8-way associativity, parity disabled */ .l2c_aux_val = 0x00000000, .l2c_aux_mask = 0xffffffff, .smp = smp_ops(zynq_smp_ops), .map_io = zynq_map_io, .init_irq = zynq_irq_init, .init_machine = zynq_init_machine, .init_late = zynq_init_late, .init_time = zynq_timer_init, .dt_compat = zynq_dt_match, .reserve = zynq_memory_init, .restart = zynq_system_reset, MACHINE_END

<code>    zynq_init_machine--->  当前的zybo的机器初始化主函数。如需上点后初始化该板子的其他外设，可以在本函数内添加相应的初始化功能。
</code>

玩过或者移植过arm-linux的都应该知道在/arch/arm目录下有许多与具体处理器相关的目录，当然对于zynq的话所对应的目录就是mach-zynq，在里面找到与具体板子相关的文件Linux-Digilent-Dev-masterarcharmmach-zynqarmcommon.c，没错，就是它。无论是出于想移植到新的内核还是出于想深入学习某一款arm等，对这个文件的学习是必不可少的。这个文件大部分内容是对平台设备的结构体初始化，在这个文件的最后有一个非常重要的宏：

<code>DT_MACHINE_START(XILINX_EP107, <span class="hljs-string">"Xilinx Zynq Platform"</span>)
    <span class="hljs-comment">/* 64KB way size, 8-way associativity, parity disabled */</span>
    <span class="hljs-preprocessor">.l</span>2c_aux_val    = <span class="hljs-number">0x00000000</span>,
    <span class="hljs-preprocessor">.l</span>2c_aux_mask   = <span class="hljs-number">0xffffffff</span>,
    <span class="hljs-preprocessor">.smp</span>        = smp_ops(zynq_smp_ops),
    <span class="hljs-preprocessor">.map</span>_io     = zynq_map_io,
    <span class="hljs-preprocessor">.init</span>_irq   = zynq_irq_init,
    <span class="hljs-preprocessor">.init</span>_machine   = zynq_init_machine,
    <span class="hljs-preprocessor">.init</span>_late  = zynq_init_late,
    <span class="hljs-preprocessor">.init</span>_time  = zynq_timer_init,
    <span class="hljs-preprocessor">.dt</span>_compat  = zynq_dt_match,
    <span class="hljs-preprocessor">.reserve</span>    = zynq_memory_init,
    <span class="hljs-preprocessor">.restart</span>    = zynq_system_reset,
MACHINE_END</code>

DT_:qMACHINE_START的定义在arch/arm/include/asm/mach/arch.h，如下：

<code><span class="hljs-preprocessor">#<span class="hljs-keyword">define</span> DT_MACHINE_START(_name, _namestr)               </span>
<span class="hljs-keyword">static</span> <span class="hljs-keyword">const</span> <span class="hljs-keyword">struct</span> machine_desc __mach_desc_<span class="hljs-preprocessor">##_name    </span>
 __used                                                  __attribute__((__section__(<span class="hljs-string">".arch.info.init"</span>))) = {            .nr             = ~<span class="hljs-number">0</span>,                                   .name           = _namestr,

<span class="hljs-preprocessor">#<span class="hljs-keyword">endif</span></span></code>

噢，其实就是定义了一个struct machine_desc类型结构体变量，这个结构体还定义了其他一些成员，接下来着重关注.init_machine这个成员，它是一个函数指针，值为zynq_init_machine，这个函数也在common.c中定义。内容是什么呢？呵呵，因为在这里只给出大体流程，具体内容先不分析。现在最关心的是这个结构体变量在哪里被调用，从而调用它里面的成员和成员函数呢？先来看/arch/arm/kernel/setup.c里面的setup_arch()函数：

<code><span class="hljs-literal">void</span> __init setup_arch(char <span class="hljs-subst">**</span>cmdline_p)
{
    const struct machine_desc <span class="hljs-subst">*</span>mdesc;

    setup_processor();
    mdesc <span class="hljs-subst">=</span> setup_machine_fdt(__atags_pointer);
    <span class="hljs-keyword">if</span> (<span class="hljs-subst">!</span>mdesc)
        mdesc <span class="hljs-subst">=</span> setup_machine_tags(__atags_pointer, __machine_arch_type);
    machine_desc <span class="hljs-subst">=</span> mdesc;
    machine_name <span class="hljs-subst">=</span> mdesc<span class="hljs-subst">-></span>name;

    <span class="hljs-keyword">if</span> (mdesc<span class="hljs-subst">-></span>reboot_mode <span class="hljs-subst">!=</span> REBOOT_HARD)
        reboot_mode <span class="hljs-subst">=</span> mdesc<span class="hljs-subst">-></span>reboot_mode;

    init_mm<span class="hljs-built_in">.</span>start_code <span class="hljs-subst">=</span> (unsigned long) _text;
    init_mm<span class="hljs-built_in">.</span>end_code   <span class="hljs-subst">=</span> (unsigned long) _etext;
    init_mm<span class="hljs-built_in">.</span>end_data   <span class="hljs-subst">=</span> (unsigned long) _edata;
    init_mm<span class="hljs-built_in">.</span>brk    <span class="hljs-subst">=</span> (unsigned long) _end;

    <span class="hljs-comment">/* populate cmd_line too for later use, preserving boot_command_line */</span>
    strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);
    <span class="hljs-subst">*</span>cmdline_p <span class="hljs-subst">=</span> cmd_line;

    parse_early_param();

    early_paging_init(mdesc, lookup_processor_type(read_cpuid_id()));
    setup_dma_zone(mdesc);
    sanity_check_meminfo();
    arm_memblock_init(mdesc);

    paging_init(mdesc);
    request_standard_resources(mdesc);

    <span class="hljs-keyword">if</span> (mdesc<span class="hljs-subst">-></span>restart)
        arm_pm_restart <span class="hljs-subst">=</span> mdesc<span class="hljs-subst">-></span>restart;

    unflatten_device_tree();

    arm_dt_init_cpu_maps();
    psci_init();
    <span class="hljs-attribute">...</span><span class="hljs-attribute">...</span><span class="hljs-attribute">...</span><span class="hljs-attribute">...</span><span class="hljs-attribute">...</span><span class="hljs-attribute">...</span><span class="hljs-attribute">...</span><span class="hljs-built_in">.</span></code>

这个函数在/init/main.c的start_kernel()函数里被调用。看到第10行，这里的setup_machine()函数的作用就是找到我们想要的struct machine_desc类型的变量，也就是在common.c里定义那个变量。函数的参数machine_arch_type的值是什么呢？继续看：

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[Zedboard Linux系统移植]-从MACHINE_START开始

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