linux-kernel - Re: [PATCH v2 0/7] tty: add flag to suppress ready signalling on open

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Message-ID: <X9HlA17uI7I3Cuxw@kroah.com>
Date:   Thu, 10 Dec 2020 10:06:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Mychaela Falconia <mychaela.falconia@...il.com>
Cc:     Johan Hovold <johan@...nel.org>, Jiri Slaby <jirislaby@...nel.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 v2 0/7] tty: add flag to suppress ready signalling on open

On Wed, Dec 09, 2020 at 02:49:45PM -0800, Mychaela Falconia wrote:
> Greg K-H wrote:
> 
> > I think we need more review for the rest of the series.  This does
> > change the way serial ports work in a non-traditional way (i.e. using
> > sysfs instead of terminal settings).
> 
> But the problem is that the current status quo is fundamentally broken
> for those hardware devices in which DTR and/or RTS have been repurposed
> for something other than modem and flow control.  Right now whenever a
> "cold" (never previously opened) serial port is opened for the first
> time, that open action immediately and unstoppably asserts both DTR
> and RTS hardware outputs, without giving userspace any opportunity to
> say "no, please don't do it".  Yes, this behaviour is codified in a
> bunch of standards that ultimately trace back to 1970s Original UNIX,
> but just because it is a standard does not make it right - this
> Unix/POSIX/Linux "standard" serial port behaviour is a bug, not a
> feature.

Thanks for the long response, but I think you have to realize that
creating a new api for something that has been "how things work" since
the 1970's should not be taken lightly.  No matter if it was a bug or
not, changing user-visable behavior is not a trivial thing.  What we
come up with here has to stand the test of time of being able to be
supported properly for the next 40+ years.

thanks,

greg k-h