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

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Date:	Tue, 20 Nov 2012 01:32:10 -0800
From:	anish singh <anish198519851985@...il.com>
To:	Anton Vorontsov <cbouatmailru@...il.com>
Cc:	"Tc, Jenny" <jenny.tc@...el.com>,
	Chanwoo Choi <cw00.choi@...sung.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 1:24 AM, Anton Vorontsov <cbouatmailru@...il.com> wrote:
> 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...
+1 for this idea.
>
>>  * 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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