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

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Date:	Fri, 20 Feb 2015 12:40:49 -0800
From:	David Cohen <david.a.cohen@...ux.intel.com>
To:	Felipe Balbi <balbi@...com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Robert Baldyga <r.baldyga@...sung.com>,
	heikki.krogerus@...ux.intel.com,
	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: [PATCH v2] extcon: otg_gpio: add driver for USB OTG port
 controlled by GPIO(s)

On Fri, Feb 20, 2015 at 02:00:26PM -0600, Felipe Balbi wrote:
> On Fri, Feb 20, 2015 at 11:59:27AM -0800, David Cohen wrote:
> > 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@...sung.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.
> 
> you missed [1] :-)

Oops. Looks like it went away during your past reply :)

[1] https://lkml.org/lkml/2014/12/18/82

Br, David

> 
> -- 
> balbi


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