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

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Date:	Mon, 17 Mar 2014 12:03:09 +0900
From:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.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: Re: [PATCH V3] serial/uart/8250: Add tunable RX interrupt
 trigger I/F of FIFO buffers

Hi Heikki,

Thank you for your reply.

(2014/03/14 23:16), Heikki Krogerus wrote:
> 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;

Oh, I'll fix it.

>>   }
>>   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?

Ah, we don't need to set up->fcr = 0 in the previous flow when we
implement as follows:

unsigned char fcr = up->fcr;

  ... <snip> ...

     /*
      * If fcr exists, a user has opened this port, changed RX
      * trigger, or read RX trigger before. If so, we do not change
      * fcr.
      */
     if (!fcr)
         fcr = uart_config[port_type].fcr;
     if ((baud < 2400 && !up->dma) || fifo_bug) {
         fcr &= ~UART_FCR_TRIGGER_MASK;
         fcr |= UART_FCR_TRIGGER_1;
     }

up->fcr = fcr;

> <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?

In these implementation, the driver sets up->fcr as
uart_config[up->port.type].fcr first and changes only RX trigger. So,
we don't need to set the bit in a direct way.

Thank you,
Yoshihiro YUNOMAE

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@...achi.com


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