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commit bfd7bd5b49c84aac9068bff7635e94ce038475ec
parent 177c459b08a34dcf004aa9a4c1f1d8be682ff3af
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 20 Dec 2018 07:29:11 -0800

Merge tag 'tty-4.20-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

Pull tty/serial fix from Greg KH:
 "Here is a single fix, a revert, for the 8250 serial driver to resolve
  a reported problem.

  There was some attempted patches to fix the issue, but people are
  arguing about them, so reverting the patch to revert back to the 4.19
  and older behavior is the best thing to do at this late in the release
  cycle.

  The revert has been in linux-next with no reported issues"

* tag 'tty-4.20-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty:
  Revert "serial: 8250: Fix clearing FIFOs in RS485 mode again"

Diffstat:
Mdrivers/tty/serial/8250/8250_port.c | 29+++++------------------------
1 file changed, 5 insertions(+), 24 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c @@ -552,30 +552,11 @@ 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) { - /* - * 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); + 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); } } @@ -1467,7 +1448,7 @@ 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);