linux-kernel - Re: [PATCH 3/3] usb: cp210x: Add ioctl for GPIO support

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Date:	Wed, 2 May 2012 21:49:01 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Preston Fick <pffick@...il.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	preston.fick@...abs.com
Subject: Re: [PATCH 3/3] usb: cp210x: Add ioctl for GPIO support

> Actually, why can't you use the GPIO subsystem for something like this?
> Can't you export your device as both a usb-serial device and a gpio
> device and have things work properly that way?

You still need the ioctls even then in order to discover the gpio
numbers, and having done that youi've got potential races with unload
when you try and open them. You've also got permissions considerations
and synchronization between gpio and data problems.

It's not a good way to go. It might make sense in some platforms to
expose them as both but its not a good general model.

I'm currently favouring adding some 'additional control line' bits to
termiox.
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