emmc问题：

mmc1: switch to high-speed failed, err:-110

drivers/mmc/core/mmc.c

/drivers/mmc/core/mmc_ops.c

跟踪发现是：err = mmc_wait_for_cmd(host, &cmd, 0); 返回错误

修改成：err = mmc_wait_for_cmd(host, &cmd, MMC_CMD_RETRIES);

问题解决！