Re: Moxa UPort 1150 and RS-422/485… what's the "proper" way to switch modes

From: Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Alan Cox <gnomes-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org>
Cc: Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Oliver Neukum <oneukum-IBi9RG/b67k@public.gmane.org>,
	Stuart Longland
	<stuartl-3e+Fe6x+DsgJbe36r25VNhCuuivNXqWP@public.gmane.org>,
	linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: Moxa UPort 1150 and RS-422/485… what's the "proper" way to switch modes
Date: Mon, 3 Jul 2017 10:51:31 +0200	[thread overview]
Message-ID: <20170703085131.GE7084@localhost> (raw)
In-Reply-To: <20170629205032.743ab235@alans-desktop>

On Thu, Jun 29, 2017 at 08:50:32PM +0100, Alan Cox wrote:
> So IMHO there are two cases
> 
> 1. The configuration is fixed in the hardware - in which case we should
> automatically set it in kernel, or from device tree.

Right.

> 2. The configuration is soft - in which case you need an ioctl you can
> use on the port to change it - irrespective of whether sysfs also handles
> it. For simple permissions reasons and also to avoid races you need that
> ioctl.

Ok, but if we are going to extend and use the RS485 ioctl for this, I
think we should just stick to that and not add a sysfs-interface as
well.

I'll take a closer look at this.

> We intentionally have lots of spare space left to extend the RS485 ioctl,
> and we have termiox which contains even more room and historically in
> other Unixen dealt with all sorts of weird and wonderful parameters used
> on stuff like synchronous ports.

Yes, your foresight when adding (generalising) that ioctl might come in
handy now. :)

Thanks,
Johan
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