linux-kernel - Re: [PATCH 0/5] tty: add flag to suppress ready signalling on open

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Message-ID: <a58e3a7b-58bb-0430-2344-8e8155758e45@kernel.org>
Date:   Fri, 4 Dec 2020 07:58:53 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Mychaela Falconia <mychaela.falconia@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Mychaela N . Falconia" <falcon@...ecalypso.org>,
        linux-serial@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] tty: add flag to suppress ready signalling on open

On 02. 12. 20, 12:48, Johan Hovold wrote:
>>> but I question the
>>> usefulness of doing so, as it is a chicken and egg problem: one needs
>>> to open the tty device in order to do termios ioctls on it, and if
>>> that initial open triggers DTR/RTS hardware actions, then the end user
>>> is still screwed.  If Johan or someone else can see a potential use
>>> case for manipulating this new flag via termios (as opposed to sysfs
>>> or USB-ID-based driver quirks), perhaps you could elaborate on it?
>>
>> We would need to (ab)use another open flag (e.g. O_DIRECT). I am not
>> biased to either of solutions.
> 
> Forgot to mention that using open-flags would prevent using standard
> utilities like cat, echo and terminal programs. So for that reason a
> termios and/or sysfs interface is also preferred.

Nope, I meant it differently. You set it up once using the special open 
flag. Like with setserial, one sets I/O port, irqs etc. and then uses 
standard tools as the port is already set up (marked as NORDY in this case).

thanks,
-- 
js