linux-kernel - Re: [PATCH 1/2] tty: Add lookahead param to receive

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Message-ID: <cffdfa4c-57f8-a8f7-758e-2975b91d7b92@kernel.org>
Date:   Wed, 6 Apr 2022 10:07:31 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     linux-serial@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Gilles Buloz <gilles.buloz@...tron.com>,
        Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH 1/2] tty: Add lookahead param to receive_buf

On 05. 04. 22, 18:03, Andy Shevchenko wrote:
> On Tue, Apr 05, 2022 at 01:24:36PM +0300, Ilpo Järvinen wrote:
>> After lookahead for XON/XOFF characters is added by the next
>> patch, the receive side needs to ensure the flow-control
>> actions are not retaken later on when those same characters
>> get read by TTY.
>>
>> Thus, pass lookahead count to receive_buf and skip
>> flow-control character actions if already taken for the
>> character in question. Lookahead count will become live after
>> the next patch.
> 
> ...
> 
>> -static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
>> +static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c,
>> +				       bool lookahead_done)
>>   {
>>   	struct n_tty_data *ldata = tty->disc_data;
>>   
>>   	if (I_IXON(tty)) {
>>   		if (c == START_CHAR(tty)) {
>> -			start_tty(tty);
>> -			process_echoes(tty);
>> +			if (!lookahead_done) {
>> +				start_tty(tty);
>> +				process_echoes(tty);
>> +			}
>>   			return;
>>   		}
>>   		if (c == STOP_CHAR(tty)) {
>> -			stop_tty(tty);
>> +			if (!lookahead_done)
>> +				stop_tty(tty);
>>   			return;
>>   		}
> 
> Wouldn't be cleaner to inside out the conditionals?

Seconded.

> 	if (I_IXON(tty)) {
> 		if (lookahead_done) {
> 			// Can be joined, but I think this is better

I would join them, IMO it'd be still easy to read and to follow too.

> 			if (c == START_CHAR(tty))
> 				return;
> 			if (c == STOP_CHAR(tty))
> 				return;
> 		} else {
> 			if (c == START_CHAR(tty)) {
> 				start_tty(tty);
> 				process_echoes(tty);
> 				return;
> 			}
> 			if (c == STOP_CHAR(tty)) {
> 				stop_tty(tty);
> 				return;
> 			}
> 		}
> 	}

thanks,
-- 
js
suse labs