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

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Date:	Wed, 3 Apr 2013 16:56:59 +0300
From:	Felipe Balbi <balbi@...com>
To:	Felipe Balbi <balbi@...com>
CC:	Vivek Gautam <gautamvivek1987@...il.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 04:54:14PM +0300, Felipe Balbi 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.
> 
> 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);
> }
> 
> ???

and of course I missed the fact that pm_runtime_enable returns nothing
:-) But you got my point.

-- 
balbi

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