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

From: Alan Stern
Date: Tue Apr 23 2013 - 12:53:11 EST

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In reply to: Vivek Gautam: "Re: [PATCH v3 01/11] usb: phy: Add APIs for runtime power management"
Next in thread: Vivek Gautam: "Re: [PATCH v3 01/11] usb: phy: Add APIs for runtime power management"
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On Tue, 23 Apr 2013, Vivek Gautam wrote:

> >> Alright, so here's my understanding:
> >>
> >> I suggested letting e.g. DWC3 enable the PHY's runtime_pm; Alan said
> >> that it could be done before that so that DWC3 sees an enabled PHY
> >> during probe.
> >
> > Basically right. Help me to understand the overall situation a little
> > better:
> >
> > What code registers the PHY initially?
> PHY is added to global list by PHY drivers (like
> phy-samsung-usb2.c/phy-omap-usb2.c)
> by usb_add_phy() API

Then this routine should initialize the PHY. The initialized state
could be either active or suspended, your choice. Suspended would be
best, in case the PHY never gets used.

> > What routine does the DWC3 driver call to register itself
> > as a consumer of the PHY?
> I think DWC3 doesn't registers itself as consumer of PHY,
> rather it gets that PHY from
> the list using devm_usb_get_phy()/devm_usb_get_phy_by_phandle() API.
> DWC3 can now call PHY's initialization sequence using usb_phy_init().
> So, before DWC3 initializes the PHY, PHYs should be in active state.

Then usb_phy_init should make sure the PHY is in the active state. If
usb_add_phy() left the PHY suspended, then this routine should call
pm_runtime_get_sync().

After DWC3 (or any other driver) has acquired the PHY, it can call
pm_runtime_put/get() however it likes, so long as the calls balance
properly. If the driver isn't runtime-PM aware then it won't use any
of these calls, and the PHY will remain active the entire time.

> > Likewise, what routine does it call to unregister itself?
> Once DWC3's remove() is called PHYs are put.

Is there a routine analogous to usb_phy_init() that gets called when
PHY is released? That routine would do the opposite of usb_phy_init(),
putting the PHY back into its initialized state.

Alan Stern

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