linux-kernel - Re: [PATCH] extcon : callback function to read cable property

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Message-ID: <20121120092419.GA27280@lizard>
Date:	Tue, 20 Nov 2012 01:24:19 -0800
From:	Anton Vorontsov <cbouatmailru@...il.com>
To:	"Tc, Jenny" <jenny.tc@...el.com>
Cc:	Chanwoo Choi <cw00.choi@...sung.com>,
	anish singh <anish198519851985@...il.com>,
	"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"myunjoo.ham@...il.com" <myunjoo.ham@...il.com>,
	"lockwood@...roid.com" <lockwood@...roid.com>,
	"peterhuewe@....de" <peterhuewe@....de>,
	"broonie@...nsource.wolfsonmicro.com" 
	<broonie@...nsource.wolfsonmicro.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"lars@...afoo.de" <lars@...afoo.de>,
	"jic23@...nel.org" <jic23@...nel.org>,
	"Pallala, Ramakrishna" <ramakrishna.pallala@...el.com>
Subject: Re: [PATCH] extcon : callback function to read cable property

On Tue, Nov 20, 2012 at 09:14:41AM +0000, Tc, Jenny wrote:
[...]
> > For example,
> > Firstly, the power_supply charging framework check state of charger cable
> > whether attached or detached cable. Second, when power_supply charging
> > framework receive the changed state of host system from 'Host system
> > notifier', change charging current of charger cable.
> 
> Not just SUSPEND, but we need to handle RESUME , UPDATE etc.  Also this doesn’t help us to
> define a standard interface for the charger cable state/properties. IMHO it's not right
> to provide different interfaces for different cables. This doesn't help us to standardize
> the charger cable interface.
> 
> This thread has been running for a quite long time. Unfortunately we couldn't make an
> agreement on the final solution. I would like to recap the overall requirement and
> would like to propose alternate solutions. The requirements is  to
> "Provide a generic interface for charger cable states and charger cable properties"
> 
> Even though extcon subsystem handles charger cable states, it's not enough to handle
> all kind of charger cable states. It can handle just 2 states CONNECT/DISCONNECT.
> But there are scenarios where we need to handle more than 2 states
> (eg. USB SUSPEND/RESUME/UPDATE etc). Also extcon doesn't have any mechanism to
> read cable properties in a generic way.  Extcon charger-cable consumer driver
> implementations (eg charger-manager), defines charger cable properties statically (current in mA)
> inside the consumer driver. This is not enough, since the charger cable properties may change dynamically
> 
> In existing form extcon cannot support different charger cable states and their 
> properties in a generic way. Also we couldn't find a final solution on how to modify the
> extcon to support these requirements. From the whole discussion what I conclude is
>  * extcon is not designed to support cable properties

The idea of using union seemed good to me, what happened to it?

I mean, MyungJoo Ham wrote:

| We may have:
|        enum extcon_cable_type {
|                EXTCON_CT_REGULATOR,
|                EXTCON_CT_PSY,
|                EXTCON_CT_CHARGER_CB,
|                ...
|        };
| and have the following included at struct extcon_cable:
|        union {
|                struct regulator *reg;
|                struct power_supply *psy;
|                struct charger_cable *charger_cb;
|                ...
|        } cable data;
|        enum extcon_cable_type cable_type;

This sounds good to me...

>  * extcon is not designed to support any cable state other than CONNECT/DISCONNECT

Dunno for this one. Can we get these additional states via "properties" as
described above?

Thanks,
Anton.
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