我看到：
root@imx6ullevk:~# cat /sys/kernel/debug/mmc0/ios
clock: 132000000 Hz
vdd: 21 (3.3 ~ 3.4 V)
bus mode: 2 (push-pull)
chip select: 0 (don't care)
power mode: 2 (on)
bus width: 2 (4 bits)
timing spec: 6 (sd uhs SDR104)
signal voltage: 1 (1.80 V)
driver type: 0 (driver type B)
如何让接口使用 200MHz 时钟？我应该在设备树中放什么？
