Messages in this thread | | | Date | Tue, 3 Jan 2012 10:37:07 -0500 | From | Dave Jones <> | Subject | serial ports now asserting DTR and RTS during boot; breaks connected hardware |
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Jiri, We got this report from a user who notes a change in behaviour for his serial hardware over the last few kernel versions.
https://bugzilla.redhat.com/show_bug.cgi?id=771010
This sounds like it might be related to your DTR/RTS changes back in March 2011 maybe ?
> Description of problem: > > After upgrade from FC14 to FC16, it was discovered that during kernel boot, the > DTR and RTS signals of serial devices (both real UART and FTDI USB devices) are > being asserted from driver load to approx 20 seconds afterward. This causes > some types of hardware connected to these ports to fail as they expect a > different sequence or controlled activation of these signals. In particular, > ham radio equipment that uses these signals to key transmitters is now going > into uncontrolled transmit for nearly the duration of kernel boot. > > > Steps to Reproduce: > 1. connect RS232 breakout box to serial port > 2. boot system > 3. watch DTR and RTS LEDs light as kernel is booting > > Actual results: > > LEDs light and stay light for almost entire boot duration indicating that DTR > and RTS are asserting as the kernel boots. > > Expected results: > > DTR and RTS should not activate while kernel is booting. They should only > activate when the port is opened by an application and it has performed a > termios function to enable these signals. > > > Additional info: > > The following code in the ftdi_sio driver is one suspect but this behavior > happens on 8250 UARTs also so it is systemic now, > > ftdi_sio.c, line 2161, > > /* Ensure RTS and DTR are raised when baudrate changed from 0 > */ > if (!old_termios || (old_termios->c_cflag & CBAUD) == B0) > set_mctrl(port, TIOCM_DTR | TIOCM_RTS); >
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