Commit 2bed8a8e authored by Daniel Jedrychowski's avatar Daniel Jedrychowski Committed by Greg Kroah-Hartman

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: default avatarDaniel Jedrychowski <avistel@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent c130b666
...@@ -1413,7 +1413,7 @@ static void __do_stop_tx_rs485(struct uart_8250_port *p) ...@@ -1413,7 +1413,7 @@ static void __do_stop_tx_rs485(struct uart_8250_port *p)
* Enable previously disabled RX interrupts. * Enable previously disabled RX interrupts.
*/ */
if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) { 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; p->ier |= UART_IER_RLSI | UART_IER_RDI;
serial_port_out(&p->port, UART_IER, p->ier); serial_port_out(&p->port, UART_IER, p->ier);
......
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