From 2bed8a8e70729f996af92042d3ad0f11870acc1f Mon Sep 17 00:00:00 2001 From: Daniel Jedrychowski Date: Mon, 12 Dec 2016 09:18:28 +1100 Subject: [PATCH] Clearing FIFOs in RS485 emulation mode causes subsequent transmits to break 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 Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_port.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index fe4399b41df6..c13fec451d03 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1413,7 +1413,7 @@ static void __do_stop_tx_rs485(struct uart_8250_port *p) * 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);