linux-kernel - Re: [PATCH] dwc3: gadget: Defer starting the gadget device until gadget is power on

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Date:	Fri, 13 May 2016 15:46:24 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Baolin Wang <baolin.wang@...aro.org>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nel.org>,
	USB <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dwc3: gadget: Defer starting the gadget device until gadget is power on


Hi,

Baolin Wang <baolin.wang@...aro.org> writes:
>>>> why does it need restart? Why is dwc3 powered off? Who powers it off?
>>>
>>> Because when the dwc3 Vbus is off (no cable pluging in now),
>>> especially for some mobile device, the system need to power off the
>>> dwc3 to save power in this situation.
>>
>> but dwc3 doesn't do this by itself, so who's doing it?
>
> Yes, the dwc3 clock is controlled by the Soc system, so the Soc system
> can disable the dwc3 clock when there is no cable plugging in.

understood.

>>>> This looks like a *really* bad power management implementation. Do you
>>>> have hibernation enabled? Do you have Clock gating enabled? Which dwc3
>>>> version are you using? How was it configured?
>>>
>>> This is not hibernation, we want to power off the dwc3 to save power
>>> when no cable plugging in. Yes, we have clock gating, at this
>>> situation we will disable the clock and shutdown the phy to save
>>> power. For mobile device, most time no cable plugging in, so we need
>>> to think about the power consuming. How do you think this requirement?
>>
>> Well, seems like you're missing *proper* runtime PM. I've been meaning
>> to work on it for weeks, but I still have a few other things to do
>> before I get to that. In any case, we don't need to do what you did
>> here. There are better ways.
>
> Make sense.

cool, if you wanna work on it, let me know and I can give some details
of what I have in mind.

-- 
balbi

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