From: Johan Hovold <johan@kernel.org>
To: Jiri Slaby <jirislaby@kernel.org>
Cc: Mychaela Falconia <mychaela.falconia@gmail.com>,
Johan Hovold <johan@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Mychaela N . Falconia" <falcon@freecalypso.org>,
linux-serial@vger.kernel.org, linux-usb@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/5] tty: add flag to suppress ready signalling on open
Date: Wed, 2 Dec 2020 12:48:17 +0100 [thread overview]
Message-ID: <X8d/Ac5Z4bT/W7ZA@localhost> (raw)
In-Reply-To: <c8f3e485-54c6-99c7-4888-6eef2e174bf6@kernel.org>
On Tue, Dec 01, 2020 at 08:14:07AM +0100, Jiri Slaby wrote:
> On 30. 11. 20, 22:22, Mychaela Falconia wrote:
> > 2) For situations in which the luxury of a custom USB ID is not
> > available, e.g., a situation where the device that does not tolerate
> > automatic DTR/RTS assertion on open is a physical RS-232 device that
> > can be connected to "any" serial port, the new sysfs attribute comes
> > to the rescue.
> >
> > Johan's patch comments say that the new flag can also be brought out
> > to termios in the future, similarly to HUPCL,
>
> The difference to other control flags is that open raises DTR/RTS in any
> case (i.e. including O_NONBLOCK) -- provided baud rate is set (and it is
> for casual serials). That means you cannot open a port to configure it
> (using e.g. setserial) without actually raising the DTR/RTS.
Right, but depending on the application this may be ok (e.g. reset and
initialise on first open after boot, which may have triggered a reset
anyway).
If control over first open is needed, the sysfs interface provides that
out-of-band.
> > 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.
Johan
next prev parent reply other threads:[~2020-12-02 11:49 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-30 15:37 [PATCH 0/5] tty: add flag to suppress ready signalling on open Johan Hovold
2020-11-30 15:37 ` [PATCH 1/5] tty: add port " Johan Hovold
2020-11-30 23:36 ` Mychaela Falconia
2020-12-01 5:49 ` Jiri Slaby
2020-12-01 7:09 ` Mychaela Falconia
2020-12-01 7:16 ` Jiri Slaby
2020-12-01 8:46 ` Johan Hovold
2020-11-30 15:37 ` [PATCH 2/5] serial: core: add sysfs attribute " Johan Hovold
2020-11-30 18:27 ` Andy Shevchenko
2020-12-01 8:21 ` Johan Hovold
2020-12-01 10:55 ` Andy Shevchenko
2020-12-01 11:05 ` Johan Hovold
2020-12-01 11:19 ` Andy Shevchenko
2020-12-01 13:22 ` Johan Hovold
2020-12-01 13:49 ` Andy Shevchenko
2020-12-01 17:43 ` Johan Hovold
2020-12-01 16:44 ` Greg Kroah-Hartman
2020-12-01 17:24 ` Johan Hovold
2020-11-30 15:37 ` [PATCH 3/5] USB: serial: " Johan Hovold
2020-11-30 18:29 ` Andy Shevchenko
2020-11-30 15:37 ` [PATCH 4/5] USB: serial: ftdi_sio: pass port to quirk port_probe functions Johan Hovold
2020-11-30 15:37 ` [PATCH 5/5] USB: serial: ftdi_sio: add support for FreeCalypso DUART28C adapter Johan Hovold
2020-12-01 6:54 ` Jiri Slaby
2020-12-01 8:55 ` Johan Hovold
2020-11-30 21:22 ` [PATCH 0/5] tty: add flag to suppress ready signalling on open Mychaela Falconia
2020-12-01 7:14 ` Jiri Slaby
2020-12-01 7:18 ` Mychaela Falconia
2020-12-02 11:48 ` Johan Hovold [this message]
2020-12-04 6:58 ` Jiri Slaby
2020-12-08 9:30 ` Johan Hovold
2020-12-01 8:40 ` Johan Hovold
2020-12-01 10:48 ` Andy Shevchenko
2020-12-01 10:58 ` Johan Hovold
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