linux-kernel - Re: [PATCH] extcon-gpio: add devicetree support.

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Date:	Mon, 4 Nov 2013 10:39:32 -0800
From:	Mark Brown <broonie@...nel.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	NeilBrown <neilb@...e.de>, MyungJoo Ham <myungjoo.ham@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Belisko Marek <marek.belisko@...il.com>,
	"Dr. H. Nikolaus Schaller" <hns@...delico.com>
Subject: Re: [PATCH] extcon-gpio: add devicetree support.

On Fri, Nov 01, 2013 at 10:16:44AM -0700, Mark Rutland wrote:
> On Fri, Nov 01, 2013 at 09:50:05AM +0000, NeilBrown wrote:

> > + - label: name for connector.  If not given, device name is used.

> Are extcon devices ever used standalone? If so, why?

They are sometimes used for things that don't have/need any other
software representation in the system like detection of attachment of
covers or as bundles for other connectors (like the Apple 30 pin cables,
they have the base connector with multiple possible things connected on
it).

> If not I see _no_ reason at all for the label property. If a userspace
> application needs to detect the presence of a particular external connector, it
> will need to know this in relation to the device the external connectors are
> attached to. In that case the application should find that device and traverse
> its set of extcon devices. The names for the external connections will be a
> property of the device, not the extcon devices themselves (along hte same lines
> as clocks), and need not be a property of the extcon device.

This is often done for user display purposes rather than for the
application and is sometimes done from the perspective of "what's
plugged into my system" (eg, helping someone cable up their system)
rather than from the point of view of using an individual device.

For example the HDA spec connector objects include information like the
connector label (ie, writing on the case) and colour as part of the
object for the connector and DMI does similar things for PCI slots.

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