linux-kernel - Re: [PATCH 4/4] usb: otg: twl4030-usb: Don't power down phy when it is in-use by charger.

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Message-ID: <20120518125010.582b191f@notabene.brown>
Date:	Fri, 18 May 2012 12:50:10 +1000
From:	NeilBrown <neilb@...e.de>
To:	Andi Shyti <andi.shyti@...il.com>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>, Felipe Balbi <balbi@...com>,
	Anton Vorontsov <cbou@...l.ru>,
	David Woodhouse <dwmw2@...radead.org>,
	Grazvydas Ignotas <notasas@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 4/4] usb: otg: twl4030-usb: Don't power down phy when it
 is in-use by charger.

On Sun, 13 May 2012 20:14:09 +0200 Andi Shyti <andi.shyti@...il.com> wrote:

> Hi,
> 
> On Wed, May 09, 2012 at 07:40:40AM +1000, NeilBrown wrote:
> > @@ -388,10 +388,16 @@ static void twl4030_phy_power(struct twl4030_usb *twl, int on)
> >  					(PHY_CLK_CTRL_CLOCKGATING_EN |
> >  						PHY_CLK_CTRL_CLK32K_EN));
> >  	} else {
> > -		__twl4030_phy_power(twl, 0);
> >  		regulator_disable(twl->usb1v5);
> >  		regulator_disable(twl->usb1v8);
> >  		regulator_disable(twl->usb3v1);
> > +		if (!regulator_is_enabled(twl->usb3v1))
> > +			/* no-one else is requesting this
> > +			 * so it is OK to power-down the
> > +			 * phy.  Sometimes a charger might
> > +			 * hold the regulator active.
> > +			 */
> > +			__twl4030_phy_power(twl, 0);
> >  	}
> 
> Usually a regulator line is shared by more than one device and
> regulator_is_enable() returns true if at least one of these
> devices is holding the regulator. This means that here the check
> will not work if this is your case.
> 
> Andi

This regulator is inside an MFD and it only feeds a very limited number of
devices within that MFD.  So I don't think there is much room for confusion.

However is it a somewhat indirect method of signalling.  I want the charger
to be able to tell the USB controller that it is using the PHY so please
don't turn it off.  Doing that through the regulator seems simple and
effective.
Maybe there is a better way, but it isn't immediately clear what that would
be.
Suggestions welcome.

Thanks,
NeilBrown

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