linux-kernel - Re: [PATCH V3] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

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Date:	Fri, 14 Mar 2014 16:16:02 +0200
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan <gnomes@...rguk.ukuu.org.uk>,
	Stephen Warren <swarren@...dia.com>,
	Jingoo Han <jg1.han@...sung.com>, linux-kernel@...r.kernel.org,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	linux-serial@...r.kernel.org, yrl.pp-manager.tt@...achi.com,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Aaron Sierra <asierra@...-inc.com>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH V3] serial/uart/8250: Add tunable RX interrupt trigger
 I/F of FIFO buffers

Hi,

On Fri, Mar 14, 2014 at 11:21:54AM +0900, Yoshihiro YUNOMAE wrote:
>  void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
>  {
> -	unsigned char fcr;
> -
>  	serial8250_clear_fifos(p);
> -	fcr = uart_config[p->port.type].fcr;
> -	serial_out(p, UART_FCR, fcr);
> +	p->fcr = uart_config[p->port.type].fcr;
> +	serial_out(p, UART_FCR, p->fcr);

You should allow also the probe drivers to set this..

        if (!p->fcr)
                p->fcr = uart_config[p->port.type].fcr;

>  }
>  EXPORT_SYMBOL_GPL(serial8250_clear_and_reinit_fifos);
>  
> @@ -2325,10 +2323,19 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>  		if ((baud < 2400 && !up->dma) || fifo_bug) {
>  			fcr &= ~UART_FCR_TRIGGER_MASK;
>  			fcr |= UART_FCR_TRIGGER_1;
> +			/* Don't use user setting RX trigger */
> +			up->fcr = 0;

I don't know about this but..

>  		}
>  	}
>  
>  	/*
> +	 * If up->fcr exists, a user has opened this port, changed RX trigger,
> +	 * or read RX trigger before. So, we don't need to change up->fcr here.
> +	 */
> +	if (!up->fcr)
> +		up->fcr = fcr;

Why not just set fcr = up->fcr in the beginning of the function?

<snip>

> +static int do_set_rx_int_trig(struct tty_port *port, unsigned char val)
> +{
> +	struct uart_state *state = container_of(port, struct uart_state, port);
> +	struct uart_port *uport = state->uart_port;
> +	struct uart_8250_port *up =
> +		container_of(uport, struct uart_8250_port, port);
> +	unsigned char fcr;
> +	int rx_trig;
> +
> +	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1)
> +		return -EINVAL;
> +
> +	rx_trig = convert_val2rxtrig(up, val);
> +	if (rx_trig < 0)
> +		return rx_trig;
> +
> +	serial8250_clear_fifos(up);
> +	if (!up->fcr)
> +		/* termios is not set yet */
> +		fcr = uart_config[up->port.type].fcr;
> +	else
> +		fcr = up->fcr;
> +	fcr &= ~UART_FCR_TRIGGER_MASK;
> +	fcr |= (unsigned char)rx_trig;
> +	up->fcr = fcr;
> +	serial_out(up, UART_FCR, up->fcr);
> +	return 0;
> +}

Where are you setting UART_FCR_ENABLE_FIFO bit? Am I missing
something?

> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
> index af47a8a..2ce1152 100644
> --- a/include/linux/serial_8250.h
> +++ b/include/linux/serial_8250.h
> @@ -76,6 +76,7 @@ struct uart_8250_port {
>  	unsigned short		bugs;		/* port bugs */
>  	unsigned int		tx_loadsz;	/* transmit fifo load size */
>  	unsigned char		acr;
> +	unsigned char		fcr;

I do like to see fcr being added here, but because of a different
reason. I want to be able to set it from the probe drivers.

Br,

-- 
heikki
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