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

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Date:	Thu, 22 Nov 2012 13:00:52 +0000
From:	"Tc, Jenny" <jenny.tc@...el.com>
To:	"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>,
	Anton Vorontsov <cbouatmailru@...il.com>,
	"Anton Vorontsov (anton.vorontsov@...aro.org)" 
	<anton.vorontsov@...aro.org>
CC:	??? <cw00.choi@...sung.com>,
	anish singh <anish198519851985@...il.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: Re: [PATCH] extcon : callback function to read cable property

> The "RFC" patch for this feature is now shown at:
> http://git.kernel.org/?p=linux/kernel/git/mzx/extcon.git;a=commit;h=5655a
> eef83addaec77a3b9387a3dd18b6c146dd5
> (Note that "for-add-feature" branch is sort of "RFC" branch)
> 
> I'm now considering relaying notifications of data updates possible via the
> notifier block of register-interest. Any inputs are welcomed.
> 
> 
> Anyway, for the USB issue of "suspend/resume at host-side and current-limit
> at device-side", we will need to 1. update regulator subsystem to have
> notification for current change (it does for enable/disable/voltage-changes)
> 2. let the charger use current-regulator 3. let the one who detects (usb
> driver?) changes at host-side change the current limit of that current-
> regulator 4. let the event from current-regulator relayed via extcon.
> We may use power-supply class as well for this issue. (may need to update if
> power-supply class does not have notifications and suspend/resume states)
> 

For this solution to work, the cable provider itself
need to register with any of these subsystems - power_supply/regulator/charger manager
IMHO a cable provider shouldn't register itself with any of the subsystem.

 For example it cannot register with power_supply subsystem
since it's not a power_supply. It's just source for a power_supply.
We register either charger/battery with power supply. I couldn't find a way
to register the cable with power supply subsystem. 

Anton,
Do you have any suggestion here?

I think the same case with regulator framework also. A cable doesn’t belong
to a regulator framework. A cable doesn’t expose any control attribute (current control/voltage
control). It just have  properties (eg current) controlled by external agents (Host machine/wall charger)

And charger manager is a consumer and not a provider. It cannot decide the charger cable capabilities.

I  have a modified version of the above patch which uses properties directly. 
https://gitorious.org/linux-charging-framework/linux-charging-framework/commit/ff358373dcb32027ebe1a267fc8b8999a3bd37e4

-jtc