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 11:00:40 +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:
> 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.

I have it half-way done. Have a look at my dwc3-fix-suspend branch on
k.org. I haven't sent because I'm not getting a PME event. Can you test
on your end and let me know what happens?

Note that if cable is disconnected, we will drop RUN/STOP bit. On
runtime_resume, we will restart the controller from scratch (skipping
memory allocations, of course)

-- 
balbi

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