Re: [PATCH] 8250.c: less than 2400 baud fix.

["gregkh@linuxfoundation.org" <gregkh@linuxfoundation.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