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

Sergei Shtylyov
2014-12-23T20:09:50Z

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...

>>> (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...
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

>>> 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