DM36X 平台USB改成host模式后，插上USB hub再接USB设备，此时设备能够正常工作；但是把USB hub去掉直接接设备，此时报错，串口信息如下，请问是什么原因，谢谢。
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串口打印信息如下：[ 103.030000] usb 1-1: new high speed USB device using musb_hdrc and address 6
[ 103.150000] usb 1-1: device descriptor read/64, error -71
[ 103.380000] usb 1-1: device descriptor read/64, error -71
[ 103.610000] usb 1-1: new high speed USB device using musb_hdrc and address 7
[ 103.730000] usb 1-1: device descriptor read/64, error -71
[ 103.960000] usb 1-1: device descriptor read/64, error -71
[ 104.190000] usb 1-1: new high speed USB device using musb_hdrc and address 8
[ 104.610000] usb 1-1: device not accepting address 8, error -71
[ 104.730000] usb 1-1: new high speed USB device using musb_hdrc and address 9
[ 105.150000] usb 1-1: device not accepting address 9, error -71
[ 108.540000] usb 1-1: new high speed USB device using musb_hdrc and address 10
[ 108.660000] usb 1-1: device descriptor read/64, error -71
[ 108.890000] usb 1-1: device descriptor read/64, error -71
[ 109.120000] usb 1-1: new high speed USB device using musb_hdrc and address 11
[ 109.240000] usb 1-1: device descriptor read/64, error -71
[ 109.470000] usb 1-1: device descriptor read/64, error -71
[ 109.700000] usb 1-1: new high speed USB device using musb_hdrc and address 12
[ 110.120000] usb 1-1: device not accepting address 12, error -71
[ 110.240000] usb 1-1: new high speed USB device using musb_hdrc and address 13
[ 110.660000] usb 1-1: device not accepting address 13, error -71
