linux-kernel - Re: [PATCH 4/4] usb: phy: twl4030: test ID resistance to see if charger is present.

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Message-ID: <20150304174017.681f4f8a@notabene.brown>
Date:	Wed, 4 Mar 2015 17:40:17 +1100
From:	NeilBrown <neilb@...e.de>
To:	Pavel Machek <pavel@....cz>
Cc:	Tony Lindgren <tony@...mide.com>, Felipe Balbi <balbi@...com>,
	Kishon Vijay Abraham I <kishon@...com>,
	linux-omap@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	GTA04 owners <gta04-owner@...delico.com>
Subject: Re: [PATCH 4/4] usb: phy: twl4030: test ID resistance to see if
 charger is present.

On Mon, 2 Mar 2015 22:04:44 +0100 Pavel Machek <pavel@....cz> wrote:

> On Tue 2015-02-24 14:40:37, NeilBrown wrote:
> > If an 'A' plug is inserted, ID should be pulled to ground.
> > If a 'B' plug, then ID should be floating.
> > 
> > If an Accessory Charger Adapter is inserted, then ID will
> > be neither grounded nor floating.  In this case tell the
> > USB subsystem that it is an A plug, and the battery
> > charging subsystem that it is a charger.
> 
> > Fortunately, this will treat the Openmoko charger (and
> > other similar chargers) as a charger.
> > 
> > Signed-off-by: NeilBrown <neilb@...e.de>
> 
> I guess signed-off-by should be "real name", so I'd add a space..

This is how I always sign-off my name (2858 times in "git log") so I don't
think I'll change it now.

> 
> Acked-by: Pavel Machek <pavel@....cz>

Thanks.

> 
> > --- a/drivers/phy/phy-twl4030-usb.c
> > +++ b/drivers/phy/phy-twl4030-usb.c
> > @@ -596,9 +596,31 @@ static irqreturn_t twl4030_usb_irq(int irq, void *_twl)
> >  	struct twl4030_usb *twl = _twl;
> >  	enum omap_musb_vbus_id_status status;
> >  	bool status_changed = false;
> > +	bool found_charger = false;
> >  
> >  	status = twl4030_usb_linkstat(twl);
> >  
> > +	if (status == OMAP_MUSB_ID_GROUND ||
> > +	    status == OMAP_MUSB_VBUS_VALID) {
> > +		/* We should check the resistance on the ID pin.
> > +		 * If not a Ground or Floating, then this is
> > +		 * likely a charger
> 
> "charger.", and I guess kernel comments should have /* on separate line.

Yep.

> 
> So it will draw .5A from the charger? 1A? 2A?
> 
> 									Pavel

That is up to the charger driver.  The phy just detects what is there, it
doesn't decide what to do with it.

Thanks,
NeilBrown

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