Could AM3352 keep USB as a peripheral alive in sleep mode?

I've implement AM3352 USB as a serial port with peripheral mode in Linux, which appears a COM port connected with PC.

If I use "echo mem>/sys/power/state" to let it enter deep sleep mode 0, the COM port disappears, which means the USB is disconnected.

I've modified the code in kernel:

Remove "omap_hwmod_idle(usb_oh);" in function am33xx_pm_suspend.

and also the M3 code:

Change "pd_per_state = PD_RET" to "pd_per_state = PD_ON" in struct deep_sleep_data ds0_data definition.

But the USB is still disconnected when it enters sleep mode.

Is there any way to keep USB alive in deep sleep mode?

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