Re: RE: [PATCH] extcon : callback function to read cable property

From: MyungJoo Ham
Date: Wed Oct 17 2012 - 03:08:27 EST

> Myunjoo/Chanwoo
> Ping...
> Could you please review this patch?
> -jtc
> > > > Subject: Re: [PATCH] extcon : callback function to read cable
> > > > property
> > > >
> > > > I think the reason why we have extcon is in first place is to only
> > > > notify the clients of cable connection and disconnection and it is
> > > > up to the client to decide what else to do with the cable such as
> > > > finding which state it is in and other details.
> > > > So I feel this should not be handled in the extcon.
> > > >
> > > > However it is up to the maintainer to decide.
> > >
> > > Once the consumer gets the notification, it needs to take some action.
> > > One of the action is to read the cable properties. This can be done by
> > > proprietary calls which is known both to the consumer and the provider.
> > > My intention is to avoid this proprietary calls. Since both the
> > > provider and consumer are communicating with the extcon subsystem , I
> > > feel having a callback function of this kind would help to avoid the
> > > use of proprietary calls. Also I agree that extcon notifier chains are
> > > used to notify the cable state (attach/detach). But if a cable has
> > > more than two states (like the charger cable) how do we support it without
> > having a callback function like this?
> > > Let the maintainer take the final decision.
> > Well this use case will keep on growing if we start factor in this kind of
> > changes and that is why I am opposed to adding any other state.
> > Maintainer?
> > >
> > >
> >


I don't think it's appropriate to declare the charger specific
properties in extcon.h. The status of a charger should be and can be
represented by an instance of regulator, power-supply-class,
or charger-manager.

Thus, we may (I'm still not sure) need to let extcon to relay
the instance (struct device? or char *devname?) with some callback
similar with get_cable_device(). However, allowing (and encouraging)
to pass void pointer of cable_props to extcon users from extcon device
appears not adequete. If the both parties can use their own "private"
data structure, why they cannot simply pass their own data witht the
"private" data channel?

- The later part of patch: NACK
- The first part of patch (callback): need to reconsider the data type.
We may get device pointer or device name that is correspondant to the
cable, which in turn, guides us to the corresponding data structure
(charger-manager, regulator, or something) However, I'm still not sure
which should be appropriate for this.

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