linux kernel --- 宏 CONFIG_CMDLINE 设置控制台 console

内核配置文件（比如arch\arm\configs\imx_v6_v7_defconfig）会配置宏 CONFIG_CMDLINE，用于某些情况下配置内核

CONFIG_CMDLINE="noinitrd console=ttymxc0,115200"

由以下代码可知，当设备树没有 bootargs，或者设置了CONFIG_CMDLINE_FORCE，则使用内核配置文件提供的CONFIG_CMDLINE

    /* Retrieve command line */
    p = of_get_flat_dt_prop(node, "bootargs", &l);
    if (p != NULL && l > 0)
        strlcpy(data, p, min(l, COMMAND_LINE_SIZE));

    /*
     * CONFIG_CMDLINE is meant to be a default in case nothing else
     * managed to set the command line, unless CONFIG_CMDLINE_FORCE
     * is set in which case we override whatever was found earlier.
     */
#ifdef CONFIG_CMDLINE
#if defined(CONFIG_CMDLINE_EXTEND)
    strlcat(data, " ", COMMAND_LINE_SIZE);
    strlcat(data, CONFIG_CMDLINE, COMMAND_LINE_SIZE);
#elif defined(CONFIG_CMDLINE_FORCE)
    strlcpy(data, CONFIG_CMDLINE, COMMAND_LINE_SIZE);
#else
    /* No arguments from boot loader, use kernel's  cmdl*/
    if (!((char *)data)[0])
        strlcpy(data, CONFIG_CMDLINE, COMMAND_LINE_SIZE);