diff options
| -rw-r--r-- | drivers/tty/serial/8250/8250_port.c | 29 |
1 files changed, 24 insertions, 5 deletions
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 3f779d25ec0c..f776b3eafb96 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -552,11 +552,30 @@ static unsigned int serial_icr_read(struct uart_8250_port *up, int offset) */ static void serial8250_clear_fifos(struct uart_8250_port *p) { + unsigned char fcr; + unsigned char clr_mask = UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT; + if (p->capabilities & UART_CAP_FIFO) { - serial_out(p, UART_FCR, UART_FCR_ENABLE_FIFO); - serial_out(p, UART_FCR, UART_FCR_ENABLE_FIFO | - UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT); - serial_out(p, UART_FCR, 0); + /* + * Make sure to avoid changing FCR[7:3] and ENABLE_FIFO bits. + * In case ENABLE_FIFO is not set, there is nothing to flush + * so just return. Furthermore, on certain implementations of + * the 8250 core, the FCR[7:3] bits may only be changed under + * specific conditions and changing them if those conditions + * are not met can have nasty side effects. One such core is + * the 8250-omap present in TI AM335x. + */ + fcr = serial_in(p, UART_FCR); + + /* FIFO is not enabled, there's nothing to clear. */ + if (!(fcr & UART_FCR_ENABLE_FIFO)) + return; + + fcr |= clr_mask; + serial_out(p, UART_FCR, fcr); + + fcr &= ~clr_mask; + serial_out(p, UART_FCR, fcr); } } @@ -1448,7 +1467,7 @@ 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_and_reinit_fifos(p); + serial8250_clear_fifos(p); p->ier |= UART_IER_RLSI | UART_IER_RDI; serial_port_out(&p->port, UART_IER, p->ier); |