Possible software flow problem in serial_core
From: Bollinger, Seth
Date: Thu Mar 20 2014 - 09:51:48 EST
We+IBk-ve recently run into a possible problem with software flow control
handling in the serial+AF8-core layer.
Here is the scenario:
1. Transmit from uart to remote device
2. Remote device sends us an XOFF
3. The tty layer receives the XOFF
4. stop+AF8-tty() - The uart transmitter is stopped (ops-+AD4-stop+AF8-tx) just as the
serial+AF8-core ring is cleared (this could trap a few bytes in the fifo).
5. Remote device sends us an XON
6. The tty layer receives the XON
7. start+AF8-tty() - However, the serial+AF8-core ring is empty, so the call to
start the uart transmitter (uart+AF8-start:ops-+AD4-start+AF8-tx) is skipped
Any window, however small, could leave bytes stuck in the transmitter
forever -- particularly if there will be no further transmission until
receiving a response.
I can't find any functionality in the drivers that accounts for this
possibility. Can you help me find how Linux serial drivers manage this
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/