Bug in 8250/serial_core suspend code.

[Uli Luckas]

Hi,
there is a bug in recent kernel's suspend code for serial drivers, at least 
for 8250 and pxa, probably others though.

When suspending (e.g. apm --suspend) a machine, the serial_core suspend code 
tries to disable modem control lines (including RTS):
http://sosdg.org/~coywolf/lxr/source/drivers/serial/serial_core.c?v=2.6;a=arm#L1926
This is needed to stop the other side of a serial link from sending any data 
after our serial port has been disabled.

Now in line 1937 ops->shutdown(port) is called. For 8250 this points to 
serial8250_shutdown, for pxa to serial_pxa_shutdown. Both call 
xxx__set_mctrl(&up->port, up->port.mctrl) which will restore the old control 
line values and reverse the intended effect.

I am not quite sure about the right approach to fixing this. Should 
uart_suspend_port set port.mctrl to 0 after saveing it's old value? Or should 
serial8250_shutdown simply set port.mctrl to 0?

Please also reply in private mail, as I am not subscribed.

Thanks for your help
Uli
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