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

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Date:	Tue, 17 May 2016 15:56:43 +0800
From:	Baolin Wang <baolin.wang@...aro.org>
To:	Felipe Balbi <balbi@...nel.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 Felipe,

On 13 May 2016 at 20:46, Felipe Balbi <balbi@...nel.org> wrote:
>
> 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.

Could you explain details to me, and I wanna continue to optimize the
power management things. Thanks.

>
> --
> balbi



-- 
Baolin.wang
Best Regards