linux-kernel - Re: [PATCH v3 01/11] usb: phy: Add APIs for runtime power management

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Message-ID: <20130403141831.GJ14680@arwen.pp.htv.fi>
Date:	Wed, 3 Apr 2013 17:18:31 +0300
From:	Felipe Balbi <balbi@...com>
To:	Vivek Gautam <gautamvivek1987@...il.com>
CC:	<balbi@...com>, Kishon Vijay Abraham I <kishon@...com>,
	Vivek Gautam <gautam.vivek@...sung.com>,
	<linux-usb@...r.kernel.org>, <linux-samsung-soc@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<gregkh@...uxfoundation.org>, <stern@...land.harvard.edu>,
	<sarah.a.sharp@...ux.intel.com>, <rob.herring@...xeda.com>,
	<kgene.kim@...sung.com>, <dianders@...omium.org>,
	<t.figa@...sung.com>, <p.paneri@...sung.com>
Subject: Re: [PATCH v3 01/11] usb: phy: Add APIs for runtime power management

Hi,

On Wed, Apr 03, 2013 at 07:40:44PM +0530, Vivek Gautam wrote:
> >> > >> >> +static inline void usb_phy_autopm_enable(struct usb_phy *x)
> >> > >> >> +{
> >> > >> >> +       if (!x || !x->dev) {
> >> > >> >> +               dev_err(x->dev, "no PHY or attached device available\n");
> >> > >> >> +               return;
> >> > >> >> +               }
> >> > >> >> +
> >> > >> >> +       pm_runtime_enable(x->dev);
> >> > >> >> +}
> >> > >> >
> >> > >> >
> >> > >> > IMO we need not have wrapper APIs for runtime_enable and runtime_disable
> >> > >> > here. Generally runtime_enable and runtime_disable is done in probe and
> >> > >> > remove of a driver respectively. So it's better to leave the
> >> > >> > runtime_enable/runtime_disable to be done in *phy provider* driver than
> >> > >> > having an API for it to be done by *phy user* driver. Felipe, what do you
> >> > >> > think?
> >> > >>
> >> > >> Thanks!!
> >> > >> That's very true, runtime_enable() and runtime_disable() calls are made by
> >> > >> *phy_provider* only. But a querry here.
> >> > >> Wouldn't in any case a PHY consumer might want to disable runtime_pm on PHY ?
> >> > >> Say, when consumer failed to suspend the PHY properly
> >> > >> (*put_sync(phy->dev)* fails), how much sure is the consumer about the
> >> > >> state of PHY ?
> >> > >
> >> > > no no, wait a minute. We might not want to enable runtime pm for the PHY
> >> > > until the UDC says it can handle runtime pm, no ? I guess this makes a
> >> > > bit of sense (at least in my head :-p).
> >> > >
> >> > > Imagine if PHY is runtime suspended but e.g. DWC3 isn't runtime pm
> >> > > enabled... Does it make sense to leave that control to the USB
> >> > > controller drivers ?
> >> > >
> >> > > I'm open for suggestions
> >> >
> >> > Of course unless the PHY consumer can handle runtime PM for PHY,
> >> > PHY should not ideally be going into runtime_suspend.
> >> >
> >> > Actually trying out few things, here are my observations
> >> >
> >> > Enabling runtime_pm on PHY pushes PHY to go into runtime_suspend state.
> >> > But a device detection wakes up DWC3 controller, and if i don't wake
> >> > up PHY (using get_sync(phy->dev)) here
> >> > in runtime_resume() callback of DWC3, i don't get PHY back in active state.
> >> > So it becomes the duty of DWC3 controller to handle PHY's sleep and wake-up.
> >> > Thereby it becomes logical that DWC3 controller has the right to
> >> > enable runtime_pm
> >> > of PHY.
> >> >
> >> > But there's a catch here. if there are multiple consumers of PHY (like
> >> > USB2 type PHY can
> >> > have DWC3 controller as well as EHCI/OHCI or even HSGadget) then in that case,
> >> > only one of the consumer can enable runtime_pm on PHY. So who decides this.
> >> >
> >> > Aargh!! lot of confusion here :-(
> >>
> >>
> >> hmmm, maybe add a flag to struct usb_phy and check it on
> >> usb_phy_autopm_enable() ??
> >>
> >> How does usbcore handle it ? They request class drivers to pass
> >> supports_autosuspend, but while we should have a similar flag, that's
> >> not enough. We also need a flag to tell us when pm_runtime has already
> >> been enabled.
> 
> True
> 
> >>
> >> So how about:
> >>
> >> usb_phy_autopm_enable()
> >> {
> >>       if (!phy->suports_autosuspend)
> >>               return -ENOSYS;
> >>
> >>       if (phy->autosuspend_enabled)
> >>               return 0;
> >>
> >>       phy->autosuspend_enabled = true;
> >>       return pm_runtime_enable(phy->dev);
> >> }
> >>
> >> ???
> 
> Great
> 
> >
> > and of course I missed the fact that pm_runtime_enable returns nothing
> > :-) But you got my point.
> 
> Yea, this is a way around this. :-)
> 
> Just one more query :-)
> 
> Lets suppose DWC3 enables runtime_pm on USB 2 type phy,
> it will try to go into suspend state and thereby call runtime_suspend(), if any.
> And PHY will come to active state only when its consumer wakes it up,
> and this consumer is operational
> only when its related PHY is in fully functional state.
> So do we have a situation in which this PHY goes into low power state
> in its runtime_suspend(),
> resulting in non-detection of devices on further attach (since PHY is
> in low power state) ?
> 
> Will the controller (like EHCI/OHCI) be functional now ?

ehci/ohci need to cope with that by calling usb_phy_autopm_get_sync(),
right ? (so does DWC3 :-)

-- 
balbi

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