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

Felipe Balbi
2015-02-20T19:36:30Z

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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 ?

--
balbi

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