From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oliver Neukum Subject: Re: Moxa UPort 1150 and =?UTF-8?Q?RS-422=2F485=E2=80=A6?= what's the "proper" way to switch modes Date: Wed, 28 Jun 2017 11:19:09 +0200 Message-ID: <1498641549.10278.5.camel@suse.com> References: <4a469222-d48d-f498-f2db-ca582295adc3@longlandclan.id.au> <20170627090449.GG3025@localhost> <42601356-656d-57d0-d366-a0933780b8f9@longlandclan.id.au> <1498565331.30390.5.camel@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Sender: linux-usb-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Stuart Longland , Johan Hovold Cc: Alan Cox , linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-serial@vger.kernel.org Am Mittwoch, den 28.06.2017, 08:07 +1000 schrieb Stuart Longland: Hi, > >> and to select 4-wire ("full duplex") RS-485, one does: > >> # echo rs485fd > /sys/class/tty/ttyUSB0/standard > > This looks like something that people will put into udev. > > So the switch will be done via udev, but the user not necessarily > > started via udev. Looks like a race to me. > > It is a race, but unless a daemon is watching for the very moment that a > particular serial interface appears, it's one that init scripts are very > likely to win. That is precisely what a demon might do. > Short of having a flag that blocks reads/writes until a given sysfs file > is written to say "I'm ready, go ahead"… there aren't that many options > I can think of. 1) module option 2) ioctl Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html