* [PATCH] 8250.c: less than 2400 baud fix.
@ 2012-04-26 6:59 Christian Melki
2012-04-30 2:07 ` gregkh
0 siblings, 1 reply; 3+ messages in thread
From: Christian Melki @ 2012-04-26 6:59 UTC (permalink / raw)
To: gregkh@linuxfoundation.org; +Cc: linux-serial@vger.kernel.org
From: Christian Melki <christian.melki@ericsson.se>
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 <christian.melki@ericsson.se>
---
diff -urpN linux-3.3.2.orig//drivers/tty/serial/8250/8250.c linux-3.3.2/drivers/tty/serial/8250/8250.c
--- linux-3.3.2.orig//drivers/tty/serial/8250/8250.c 2012-04-25 10:31:29.000000000 +0200
+++ linux-3.3.2/drivers/tty/serial/8250/8250.c 2012-04-26 08:46:29.000000000 +0200
@@ -2299,10 +2299,11 @@ serial8250_do_set_termios(struct uart_po
quot++;
if (up->capabilities & UART_CAP_FIFO && up->port.fifosize > 1) {
- if (baud < 2400)
- fcr = UART_FCR_ENABLE_FIFO | UART_FCR_TRIGGER_1;
- else
- fcr = uart_config[up->port.type].fcr;
+ fcr = uart_config[up->port.type].fcr;
+ if (baud < 2400) {
+ fcr &= ~UART_FCR_TRIGGER_MASK;
+ fcr |= UART_FCR_TRIGGER_1;
+ }
}
/*
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] 8250.c: less than 2400 baud fix.
2012-04-26 6:59 [PATCH] 8250.c: less than 2400 baud fix Christian Melki
@ 2012-04-30 2:07 ` gregkh
2012-04-30 9:21 ` Christian Melki
0 siblings, 1 reply; 3+ messages in thread
From: gregkh @ 2012-04-30 2:07 UTC (permalink / raw)
To: Christian Melki; +Cc: linux-serial@vger.kernel.org
On Thu, Apr 26, 2012 at 08:59:50AM +0200, Christian Melki wrote:
> From: Christian Melki <christian.melki@ericsson.se>
>
> 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 <christian.melki@ericsson.se>
> ---
>
> diff -urpN linux-3.3.2.orig//drivers/tty/serial/8250/8250.c linux-3.3.2/drivers/tty/serial/8250/8250.c
> --- linux-3.3.2.orig//drivers/tty/serial/8250/8250.c 2012-04-25 10:31:29.000000000 +0200
> +++ linux-3.3.2/drivers/tty/serial/8250/8250.c 2012-04-26 08:46:29.000000000 +0200
> @@ -2299,10 +2299,11 @@ serial8250_do_set_termios(struct uart_po
> quot++;
>
> if (up->capabilities & UART_CAP_FIFO && up->port.fifosize > 1) {
> - if (baud < 2400)
> - fcr = UART_FCR_ENABLE_FIFO | UART_FCR_TRIGGER_1;
> - else
> - fcr = uart_config[up->port.type].fcr;
> + fcr = uart_config[up->port.type].fcr;
> + if (baud < 2400) {
> + fcr &= ~UART_FCR_TRIGGER_MASK;
> + fcr |= UART_FCR_TRIGGER_1;
> + }
> }
This patch doesn't apply at all to my tree, and I can't see why with a
quick glance :(
Can you redo this against the linux-next tree and resend it please?
thanks,
greg k-h
^ permalink raw reply [flat|nested] 3+ messages in thread* RE: [PATCH] 8250.c: less than 2400 baud fix.
2012-04-30 2:07 ` gregkh
@ 2012-04-30 9:21 ` Christian Melki
0 siblings, 0 replies; 3+ messages in thread
From: Christian Melki @ 2012-04-30 9:21 UTC (permalink / raw)
To: gregkh@linuxfoundation.org; +Cc: linux-serial@vger.kernel.org
Sorry about that.
Diff should have handled that simple line offset. Now it applies cleanly to my linux-next atleast.
Signed-off-by: Christian Melki <christian.melki@ericsson.se>
---
diff -urpN linux-next.orig/drivers/tty/serial/8250/8250.c linux-next/drivers/tty/serial/8250/8250.c
--- linux-next.orig/drivers/tty/serial/8250/8250.c 2012-04-30 10:58:13.000000000 +0200
+++ linux-next/drivers/tty/serial/8250/8250.c 2012-04-30 11:03:12.000000000 +0200
@@ -2259,10 +2259,11 @@ 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;
+ }
}
/*
^ permalink raw reply [flat|nested] 3+ messages in thread
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2012-04-26 6:59 [PATCH] 8250.c: less than 2400 baud fix Christian Melki
2012-04-30 2:07 ` gregkh
2012-04-30 9:21 ` Christian Melki
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