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

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Date:   Wed, 9 Dec 2020 15:30:33 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     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 02, 2020 at 12:39:35PM +0100, Johan Hovold wrote:
> This series adds a new NORDY port flag to suppress raising the
> modem-control lines on open to signal DTE readiness.
> 
> This can be used to implement a NORDY termios control flag to complement
> HUPCL, which controls lowering of the modem-control lines on final
> close.
> 
> Initially drivers can export the flag through sysfs, which also allows
> control over the lines on first open. Such an interface is implemented
> for serial core and USB serial.
> 
> The motivation for this is to allow for applications where the DTR and
> RTS lines are used for non-standard purposes (e.g. generating power-on
> and reset pulses) to open the port without undesirable side effects.
> 
> The final patches enables this flag by default for such a USB serial
> device.
> 
> Other examples include HAM-radio devices where DTR and RTS is used for
> push-to-talk and continuous-wave control and various Arduino boards
> which are reset on open unless a jumper is physically removed.
> 
> Greg, are you ok we me taking this through my tree? I'm planning on some
> follow ups to the ftdi driver and the tty/serial changes are fairly
> self-contained.
> 
> Also let me know if you prefer to hold this off for 5.12. The change is
> minimal, self-contained and low-risk, but it is a new interface and late
> in the release cycle as Andy pointed out.

I took the first 2 patches now, that was easy :)

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).  So I want to get a bunch of people
to agree that this is ok to do things this way now before taking this
new user-visible api.

thanks,

greg k-h