linux-kernel - Re: [RFC/PATCH] extcon: otg_gpio: add driver for USB OTG port controlled by GPIO(s)

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Date:	Tue, 17 Feb 2015 11:20:56 -0800
From:	David Cohen <david.a.cohen@...ux.intel.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	baolu.lu@...ux.intel.com
Subject: Re: [RFC/PATCH] extcon: otg_gpio: add driver for USB OTG port
 controlled by GPIO(s)

Hi Linus,

Thanks for reviewing.

On Thu, Jan 08, 2015 at 08:23:03PM +0100, Linus Walleij wrote:
> On Mon, Dec 22, 2014 at 11:43 PM, David Cohen
> <david.a.cohen@...ux.intel.com> wrote:
> 
> > Some platforms have an USB OTG port fully (or partially) controlled by
> > GPIOs:
> >
> > (1) USB ID is connected directly to GPIO
> >
> > Optionally:
> > (2) VBUS is enabled by a GPIO (when ID is grounded)
> > (3) Platform has 2 USB controllers connected to same port: one for
> >     device and one for host role. D+/- are switched between phys
> >     by GPIO.
> >
> > As per initial version, this driver has the duty to control whether
> > USB-Host cable is plugged in or not:
> >  - If yes, OTG port is configured for host role
> >  - If no, by standard, the OTG port is configured for device role
> >
> > Signed-off-by: David Cohen <david.a.cohen@...ux.intel.com>
> 
> Pretty interesting! I don't understand the USB stuff so commenting
> from a GPIO side of things only.
> 
> > +config EXTCON_OTG_GPIO
> > +       tristate "VIRTUAL USB OTG PORT support"
> > +       depends on GPIOLIB
> 
> Isn't it dependent on ACPI? This was mentioned in the commit message.

Yep, I'll add it :)

> 
> > +/*
> > + * Virtual USB OTG Port driver controlled by gpios
> > + *
> > + * Copyright (c) 2014, Intel Corporation.
> > + * Author: David Cohen <david.a.cohen@...ux.intel.com>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + */
> > +
> > +#include <linux/acpi.h>
> > +#include <linux/extcon.h>
> > +#include <linux/gpio.h>
> 
> You should include <linux/gpio/consumer.h>
> 
> And nothing else. (I think it'll just work.)

It should work. I'll fix it.

> 
> > +static int __init vuport_init(void)
> > +{
> > +       return platform_driver_register(&vuport_driver);
> > +}
> > +subsys_initcall(vuport_init);
> 
> Usually we try to avoid this kind of early initcalls.
> Doesn't deferred probe work as intended?

Yeah, deferred probe is a better thing to try here.

Br, David

> 
> Yours,
> Linus Walleij
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