SD卡电压切换部分代码

    /*
     * In case CCS and S18A in the response is set, start Signal Voltage
     * Switch procedure. SPI mode doesn't support CMD11.
     */
    if (!mmc_host_is_spi(host) && rocr &&
       ((*rocr & 0x41000000) == 0x41000000)) {
        err = mmc_set_uhs_voltage(host, pocr);
        if (err == -EAGAIN) {
            retries--;
            goto try_again;
        } else if (err) {
            retries = 0;
            goto try_again;
        }
    }