From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-Id: <20120527002515.541379086@linuxfoundation.org> Date: Sun, 27 May 2012 09:25:46 +0900 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Christian Melki Subject: [ 40/91] 8250.c: less than 2400 baud fix. In-Reply-To: <20120527010903.GA18244@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Melki commit f9a9111b540fd67db5dab332f4b83d86c90e27b1 upstream. We noticed that we were loosing data at speed less than 2400 baud. It turned out our (TI16750 compatible) uart with 64 byte outgoing fifo was truncated to 16 byte (bit 5 sets fifo len) when modifying the fcr reg. The input code still fills the buffer with 64 bytes if I remember correctly and thus data is lost. Our fix was to remove whiping of the fcr content and just add the TRIGGER_1 which we want for latency. I can't see why this would not work on less than 2400 always, for all uarts ... Otherwise one would have to make sure the filling of the fifo re-checks the current state of available fifo size (urrk). Signed-off-by: Christian Melki Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) --- a/drivers/tty/serial/8250/8250.c +++ b/drivers/tty/serial/8250/8250.c @@ -2280,10 +2280,11 @@ serial8250_do_set_termios(struct uart_po quot++; if (up->capabilities & UART_CAP_FIFO && port->fifosize > 1) { - if (baud < 2400) - fcr = UART_FCR_ENABLE_FIFO | UART_FCR_TRIGGER_1; - else - fcr = uart_config[port->type].fcr; + fcr = uart_config[port->type].fcr; + if (baud < 2400) { + fcr &= ~UART_FCR_TRIGGER_MASK; + fcr |= UART_FCR_TRIGGER_1; + } } /*