第一种:手动设置
串口连接上板子后进入到下面的目录：
cd sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100
su一下：
rk3326_m2g:/sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100 $ su
然后输入下面的命令：
echo host > otg_mode
第二种烧写固件：
修改路径：px30_android8.1/device/rockchip/rk3326
修改文件：init.rk3326.rc
chown system system /sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100/otg_mode
chmod 0666 /sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100/otg_mode
write /sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100/otg_mode otg
结果如下：
1|rk3326_m2g:/sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100 # echo host > otg_mode
rk3326_m2g:/sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100 # [ 634.484788] android_work: sent uevent USB_STATE=DISCONNECTED
[ 636.994373] init: processing action (sys.usb.config=none && sys.usb.configfs=1) from (init.rk30board.usb.rc:31)
[ 636.995650] init: processing action (sys.usb.config=none && sys.usb.configfs=1) from (/init.usb.configfs.rc:1)
[ 636.998630] android_work: did not send uevent (0 0 (null))
[ 636.998750] configfs-gadget gadget: unbind function 'Function FS Gadget'/ffffffc03a456038
[ 636.998921] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.998961] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.998991] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.999021] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.999050] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.999080] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.999110] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.999140] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.999170] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.999199] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.999229] dwc2 ff300000.usb: dwc2_hsotg_ep_disable: called in host mode?
[ 636.999971] init: Sending signal 9 to service 'adbd' (pid 910) process group...
[ 637.030703] init: Successfully killed process cgroup uid 0 pid 910 in 30ms
[ 637.035618] init: Service 'adbd' (pid 910) killed by signal 9
[ 637.044370] init: processing action (init.svc.adbd=stopped) from (init.rk30board.usb.rc:35)
[ 637.044484] init: processing action (init.svc.adbd=stopped) from (/init.usb.configfs.rc:15)
[ 637.047914] init: processing action (sys.usb.config=adb && sys.usb.configfs=1) from (init.rk30board.usb.rc:64)
[ 637.048155] init: processing action (sys.usb.config=adb && sys.usb.configfs=1) from (/init.usb.configfs.rc:18)
[ 637.048268] init: starting service 'adbd'...
[ 637.049618] init: property_set("ro.boottime.adbd", "637108098228") failed: property already set
[ 637.050903] init: Created socket '/dev/socket/adbd', mode 660, user 1000, group 1000
[ 637.061640] read descriptors
[ 637.061691] read strings
[ 637.062733] init: processing action (sys.usb.config=adb && sys.usb.configfs=1 && sys.usb.ffs.ready=1) from (/init.usb.configfs.rc:21)
[ 637.065241] dwc2 ff300000.usb: bound driver configfs-gadget
没有切换之前是发现一个ADB设备，切换之后如下图片（没有发现设备）：
host切换设置：
修改路径：px30_android8.1/device/rockchip/rk3326
修改文件：init.rk3326.rc
chown system system /sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100/otg_mode
chmod 0666 /sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100/otg_mode
write /sys/devices/platform/ff2c0000.syscon/ff2c0000.syscon:usb2-phy@100/otg_mode host