From: Alan Stern <stern@rowland.harvard.edu>
To: Oliver Neukum <oneukum@suse.com>
Cc: Simon Arlott <simon@octiron.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>,
linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
linux-serial@vger.kernel.org
Subject: Re: [PATCH] USB: cdc-acm: expose serial close_delay and closing_wait in sysfs
Date: Thu, 24 Aug 2023 21:53:28 -0400 [thread overview]
Message-ID: <d1658254-b65b-4e2e-8c22-45008374d6eb@rowland.harvard.edu> (raw)
In-Reply-To: <f1b001d8-4d6c-8c9d-a90c-7d97294b66b4@suse.com>
On Fri, Aug 25, 2023 at 01:46:15AM +0200, Oliver Neukum wrote:
>
>
> On 24.08.23 20:02, Simon Arlott wrote:
> > The ioctl can't be used without opening and closing the tty, which has
> > side effects. On open() it'll raise DTR/RTS and activate it. For cdc-acm
> > that will indicate to the device that the serial port has been opened
> > which will be visible to the software running on the USB device. On
> > close() it'll be delayed by the close_delay if any process is currently
> > doing a blocking open() and there's no carrier, then the closing_wait
> > time if there's been any incomplete transmitted data (by any process).
>
> And that is an issue of the generic serial layer.
Is it feasible to add a sysfs attribute for ttys or the serial layer to
control the side effect of opening (avoid raising DTR/RTS)? If that
could be done, a program could use the existing ioctl to set close_delay
and closing_wait to 0 with no penalties.
This would be racy, but for the purposes of udev that shouldn't matter
much.
Alan Stern
prev parent reply other threads:[~2023-08-25 1:54 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-23 20:37 [PATCH] USB: cdc-acm: expose serial close_delay and closing_wait in sysfs Simon Arlott
2023-08-23 21:12 ` [PATCH (v2)] " Simon Arlott
2023-08-24 7:18 ` [PATCH] docs: ABI: sysfs-tty: close times are in hundredths of a second Simon Arlott
2023-08-25 5:33 ` Jiri Slaby
2023-08-27 18:23 ` [PATCH (v2)] docs: ABI: sysfs-tty: close times are in centiseconds Simon Arlott
2023-08-24 8:21 ` [PATCH] USB: cdc-acm: expose serial close_delay and closing_wait in sysfs Oliver Neukum
2023-08-24 14:48 ` Greg Kroah-Hartman
2023-08-24 18:02 ` Simon Arlott
2023-08-24 19:22 ` Greg Kroah-Hartman
2023-08-27 15:36 ` Simon Arlott
2023-08-24 23:46 ` Oliver Neukum
2023-08-25 1:53 ` Alan Stern [this message]
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