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

David Cohen
2014-12-23T20:42:10Z

On Tue, Dec 23, 2014 at 11:09:44PM +0300, Sergei Shtylyov wrote:
> Hello.
>
> On 12/23/2014 10:57 PM, David Cohen 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)
>
> >> Can't the host driver still control Vbus?
>
> >I can't a clean way for host driver to control VBUS considering it
> >depends on USB ID.
>
> You're using the cable state notifiers, why not control Vbus from there?
> You need some way of passing the GPIO to host driver though... I assume
> you're not using the device tree, and your host controllers live on PCI, so
> the platform data is out of question. You may be right then...

Yes to all questions :)

>
> >>>(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@linux.intel.com>
> >>>---
>
> >>>Hi,
>
> >>>Some Intel Bay Trail boards have an unusual way to handle the USB OTG port:
> >>> - The USB ID pin is connected directly to GPIO on SoC
> >>> - When in host role, VBUS is provided by enabling a GPIO
> >>> - Device and host roles are supported by 2 independent controllers with D+/-
> >>> pins from port switched between different phys according a GPIO level.
>
> >>>The ACPI table describes this USB port as a (virtual) device with all the
> >>>necessary GPIOs. This driver implements support to this virtual device as an
> >>>extcon class driver. All drivers that depend on the USB OTG port state (USB phy,
> >>>PMIC, charge detection) will listen to extcon events.
>
> >> It's very close to my setup on R-Car R8A7791 based boards. :-)
> >>I have already submitted Maxim MAX3355 OTG chip GPIO-based driver.
>
> >Hm. I'll look for it. Thanks for pointing.
>
> http://marc.info/?l=linux-usb&m=141825413802370
> In my case, Vbus is not controlled via GPIO though. I would have probably
> used the generic GPIO extcon driver if I didn't have to drive MAX3355's
> SHDN# pin high...

Besides the USB ID, I need to control VBUS and the D+/- switch. We have
a new use case coming soon that may need to add a second switch control.

> There were also some other patches for this issue, the one probably
> interesting to you is there:
>
> http://marc.info/?l=linux-usb&m=141877180912359

This one is interesting, but I'm restricted to ACPI and to the DSDTs already
released.
E.g. http://www.androidauthority.com/trekstor-xintron-lollipop-564364/

Br, David

>
> >>>Comments are welcome.
>
> >>>Br, David
>
> [...]
>
> >>>+static int __init vuport_init(void)
> >>>+{
> >>>+ return platform_driver_register(&vuport_driver);
> >>>+}
> >>>+subsys_initcall(vuport_init);
>
> >> Hm, why?
>
> >We have drivers that depend on this one during their probe.
>
> What about deferred probing? With EPROBE_DEFER we don't need to play the
> initcall games any more AFAIU.
>
> >Br, David
>
> WBR, Sergei
>