Hardware Environment: x86, arm (pxa) Problem Description: 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?
Not sure, just select one method and post a patch for review... or is it fixed already?
Any progress here?
No Progress. I posted a patch (1) which was discussed on the linux-arm-kernel mailinglist (2). As my patch breaks other things it got rejectd. 1) http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=3498/1 2) http://www.spinics.net/lists/arm-kernel/msg33755.html
TBH I can't see any way to solve this. The choice is: we fix this and break some well defined POSIX behaviour, or we don't fix this and we keep the well defined POSIX behaviour. I'm afraid this bug gives way to not introducing a regression.
I see. So, should we reject the bug and say we're not fixing it?
So what was the verdict? Anyone else might help to make decision? Thanks.
OK, it looks like we won't be fixing this. hm.