This is a note to let you know that I've just added the patch titled Clearing FIFOs in RS485 emulation mode causes subsequent transmits to break to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: clearing-fifos-in-rs485-emulation-mode-causes-subsequent-transmits-to-break.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 2bed8a8e70729f996af92042d3ad0f11870acc1f Mon Sep 17 00:00:00 2001 From: Daniel Jedrychowski <avistel@xxxxxxxxx> Date: Mon, 12 Dec 2016 09:18:28 +1100 Subject: Clearing FIFOs in RS485 emulation mode causes subsequent transmits to break From: Daniel Jedrychowski <avistel@xxxxxxxxx> commit 2bed8a8e70729f996af92042d3ad0f11870acc1f upstream. When in RS485 emulation mode, __do_stop_tx_rs485() calls serial8250_clear_fifos(). This not only clears the FIFOs, but also sets all bits in their control register (UART_FCR) to 0. One of the effects of this is the disabling of the FIFOs, which turns them into single-byte holding registers. The rest of the driver doesn't know this, which results in the lions share of characters passed into a write call to be dropped. (I can supply logic analyzer screenshots if necessary) This fix replaces the serial8250_clear_fifos() call to serial8250_clear_and_reinit_fifos() - this prevents the "dropped characters" issue from manifesting again while retaining the requirement of clearing the RX FIFO after transmission if the SER_RS485_RX_DURING_TX flag is disabled. Signed-off-by: Daniel Jedrychowski <avistel@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/tty/serial/8250/8250_port.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1411,7 +1411,7 @@ static void __do_stop_tx_rs485(struct ua * Enable previously disabled RX interrupts. */ if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) { - serial8250_clear_fifos(p); + serial8250_clear_and_reinit_fifos(p); p->ier |= UART_IER_RLSI | UART_IER_RDI; serial_port_out(&p->port, UART_IER, p->ier); Patches currently in stable-queue which might be from avistel@xxxxxxxxx are queue-4.9/clearing-fifos-in-rs485-emulation-mode-causes-subsequent-transmits-to-break.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html