Re: [PATCH v2] extcon: otg_gpio: add driver for USB OTG port controlled by GPIO(s)

From: David Cohen <david.a.cohen@linux.intel.com>
To: Felipe Balbi <balbi@ti.com>
Cc: Linus Walleij <linus.walleij@linaro.org>,
	Robert Baldyga <r.baldyga@samsung.com>,
	heikki.krogerus@linux.intel.com,
	MyungJoo Ham <myungjoo.ham@samsung.com>,
	Chanwoo Choi <cw00.choi@samsung.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	baolu.lu@linux.intel.com
Subject: Re: [PATCH v2] extcon: otg_gpio: add driver for USB OTG port controlled by GPIO(s)
Date: Fri, 20 Feb 2015 11:59:27 -0800	[thread overview]
Message-ID: <20150220195927.GE15303@psi-dev26.jf.intel.com> (raw)
In-Reply-To: <20150220193606.GA12522@saruman.tx.rr.com>

On Fri, Feb 20, 2015 at 01:36:06PM -0600, Felipe Balbi wrote:
> On Fri, Feb 20, 2015 at 11:17:00AM -0800, David Cohen wrote:
> > Hi Linus and Robert,
> > 
> > CC'ing Heikki as it involves a RFC from him.
> > 
> > On Fri, Feb 20, 2015 at 10:53:44AM +0100, Linus Walleij wrote:
> > > On Fri, Feb 20, 2015 at 7:41 AM, Robert Baldyga <r.baldyga@samsung.com> wrote:
> > > > Hi David,
> > > >
> > > > On 02/19/2015 08:59 PM, David Cohen wrote:
> > > >> Some Intel platforms have an USB OTG port fully (or partially)
> > > >> controlled by GPIOs:
> > > >>
> > > >> (1) USB ID is connected directly to a pulled up GPIO.
> > > >>
> > > >> Optionally:
> > > >> (2) VBUS is enabled/disabled by a GPIO
> > > >> (3) Platform has 2 USB controllers connected to same port: one for
> > > >>     device and one for host role. D+/- are switched between phys.
> > > >>     according to this GPIO level.
> > > >>
> > > >> This driver configures USB OTG port for device or host role according to
> > > >> USB ID value.
> > > >>  - If USB ID's GPIO level is low, OTG port is configured for host role
> > > >>    by sourcing VBUS and switching D+/- to host phy.
> > > >>  - If USB ID's GPIO level is high, by standard, the OTG port is
> > > >>    configured for device role by not sourcing VBUS and switching D+/- to
> > > >>    device controller.
> > > >
> > > > IMO it's not very elegant to handle VBUS power on/off in extcon driver.
> > > > Creating fixed regulator would allow to make VBUS handling more generic.
> > 
> > I agree. But please, see below.
> > 
> > > 
> > > IMHO it's just layers of abstraction piled on top of each other here.
> > > 
> > > I would put this adjacent to the phy driver somewhere in drivers/usb/*
> > > and make the actual USB-driver thing handle its GPIOs directly.
> > > But I guess David and Felipe have already discussed that as we're
> > > seeing this patch?
> > 
> > Felipe suggested to "divide to conquer" instead of having a single
> > extcon driver to handle all these functions:
> > 
> > - The mux functions would be controlled by a possible new pinctrl-gpio
> > driver (Linus, your input here would be nice :)
> > - The VBUS would be a fixed regulator
> > - The USB ID would make usage of existent extcon-gpio
> > 
> > But the on fw side, this is a single ACPI device representing a virtual
> > device for USB OTG port, which is nothing but a bunch of independent
> > GPIOs.
> > 
> > I could make a mfd driver to register devices for those simpler and more
> > generic drivers, but according to [1] community recognized it as a hack
> > with ACPI since I'd need to give them the GPIO without requesting on
> > mfd.
> > 
> > I'm open for suggestions :)
> 
> use MFD to create children devices and pass the required data to each
> one ?

I'd need to lookup GPIOs via ACPI without requesting them on mfd driver
and then give them to children devices.
Heikki proposed a way to do that on [1], but it got nack'ed by community.

Br, David

> 
> -- 
> balbi