There is a scenario about cdc-acm utilization.Application opens
n_gsm tty and cdc-acm tty. cdc-acm tty connects to xhci device.
The application configures cdc-adm tty to n_gsm tty as ldisc tty.
n_gsm=>cdc-acm=>xhci driver
acm_tty_write can be called from n_gsm driver by ldisc connection,
and from application when application opens cdc-acm tty directly.
acm_tty_write wakes up the device by calling usb_autopm_get_interface_async,
which calls pm_runtime_get. However, pm_runtime_get can't wake up
the device before returning as it's an async wake up. Then, acm_tty_write
might access the device when it is off.
The patchset fixes it by:
1) add a new function usb_autopm_get_interface_upgrade to deal with
above 2 requirements;
2) wake up device in n_gsm driver if n_gsm drivers calls cdc-acm driver;
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