This is a note to let you know that I've just added the patch titled
8250.c: less than 2400 baud fix.
to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-next branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will also will be merged in the next major kernel release
during the merge window.
If you have any questions about this process, please let me know.
>From f9a9111b540fd67db5dab332f4b83d86c90e27b1 Mon Sep 17 00:00:00 2001
From: Christian Melki <[email protected]>
Date: Mon, 30 Apr 2012 11:21:26 +0200
Subject: 8250.c: less than 2400 baud fix.
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 <[email protected]>
Cc: stable <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/tty/serial/8250/8250.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/8250/8250.c b/drivers/tty/serial/8250/8250.c
index 182efcc..c9ac4ea 100644
--- a/drivers/tty/serial/8250/8250.c
+++ b/drivers/tty/serial/8250/8250.c
@@ -2259,10 +2259,11 @@ serial8250_do_set_termios(struct uart_port *port,
struct ktermios *termios,
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;
+ }
}
/*
--
1.7.10
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