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Date: Wed, 30 Nov 2011 15:34:05 +0900
From: Greg KH <gregkh@suse.de>
To: Morten CHRISTIANSEN <morten.christiansen@stericsson.com>
Cc: Linus Walleij <linus.walleij@linaro.org>, NeilBrown <neilb@suse.de>,
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        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Mian Yousaf KAUKAB <mian.yousaf.kaukab@stericsson.com>
Subject: Re: [RFC PATCH 0/3] introduce: Multistate Switch Class
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On Mon, Nov 28, 2011 at 04:09:47PM +0100, Morten CHRISTIANSEN wrote:
> Hello!
> 
> Linus is correct. However some more info might be useful? Feel free to drop off whenever in the more and more detailed explanations! This is a non-trivial issue that has had some effort spent on it already.
> 
> SUMMARY: Devices today charge at high current (1.5A) from a dedicated charger and 500mA max from a standard USB port, using the standard MaxPower parameter. It would have been great if devices could also charge at higher current from a host or hub port but that is not really practical due to HW issues, not SW issues. See below. A new USB Power Delivery spec is imminent that might be of interest?
> 
> SHORT VERSION OF PREVIOUS EFFORTS:
> Using HID for managing USB battery charging current from the host is indeed the correct approach. And a work effort in USB Device Working Group went all the way to "ready for publication" state - and then died (for a number of reasons) some years ago. (Due to IPR reasons I cannot forward the un-released version of the spec.)
> 
> I see no reason to revisit the HID approach since it will not get any device support. Even if it was the correct approach.

<snip>

thanks a lot for the information, it was very helpful.

greg k-h