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

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Message-ID: <CAHp75Vczx=qjNed-8nwm6iSq5sxUKE2mXzPSd70zUxumZ5sANQ@mail.gmail.com>
Date:   Tue, 1 Dec 2020 12:48:48 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Mychaela Falconia <mychaela.falconia@...il.com>
Cc:     Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "Mychaela N . Falconia" <falcon@...ecalypso.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        USB <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/5] tty: add flag to suppress ready signalling on open

On Mon, Nov 30, 2020 at 11:25 PM Mychaela Falconia
<mychaela.falconia@...il.com> wrote:

...

> Johan's patch comments say that the new flag can also be brought out
> to termios in the future, similarly to HUPCL, 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?

Thanks for the very detailed description of what you are working on.
Unfortunately I have no thoughts about alternative solutions.

> Andy Shevchenko wrote:
>
> > > Add a nordy sysfs attribute to suppress raising the modem-control lines
> > > on open to signal DTE readiness.
> >
> > Why not call it nomctrl ?
>
> I have no opinion one way or another as to what the new sysfs attribute
> should be called - my use case won't involve this sysfs mechanism at
> all, instead I care much more about the path where the tty port flag
> gets set via a driver quirk upon seeing my custom USB ID. :)

Then why do we bother with sysfs right now? It's an ABI and Johan is
completely aware and knows that once it's in the kernel it is close to
being carved in stone.
I would vote to remove sysfs from now and see if we really need it in
the future.

-- 
With Best Regards,
Andy Shevchenko