[Regulator] Request for clarification - GPIO controlled regulator, USB VBUS,

From: Åukasz Majewski
Date: Tue Oct 03 2017 - 14:17:31 EST

Dear All,

Maybe somebody could shed some light to following issue:

On my setup I do have USB connected touchscreen powered from VBUS.

The VBUS power is controlled by a GPIO pin, which in turn is governed by regulator API:

reg_usbh1_vbus: usb-h1-vbus {
compatible = "regulator-fixed";
gpio = <&gpio3 31 GPIO_ACTIVE_LOW>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_usbh1_vbus>;
regulator-name = "usb_h1_vbus";
regulator-min-microvolt = <5000000>;
regulator-max-microvolt = <5000000>;
regulator-settling-time-us = <100000>;

This regulator is then passed to USB controller:

&usbh1 {
vbus-supply = <&reg_usbh1_vbus>;


The regulator API starts VBUS -> USB host get info about the VBUS present and starts enumeration of the USB device.

I would like to ask if there is any recommended way to remove VBUS power and have a way to force from user space the touchscreen (re-)enumeration?

As fair as I know the Regulator API is RO on purpose, so I cannot toggle vbus from there.

I could use hacks presented here (the userspace-regulator API):

but for some reason they did not find the way to the upstream. Also it seems like such approach is for testing, not for production system.

I could write a "dummy" regulator driver, which would export control API to /dev/sys/proc.
Something like:

(but with opposite way).

or ./drivers/input/misc/regulator-haptic.c

I've also tried the "usb" power control tricks;

echo "0" > /sys/bus/usb/devices/usb1/power/autosuspend_delay_ms
echo "auto" > /sys/bus/usb/devices/usb1/power/control

But without any effect (probably because of above dependencies).

Have I overlooked something? Maybe there is any other mainline code, which I could reuse?

My goal is to reuse as much as possible from ML and avoid developing any new code :-)

Thanks in advance,

Best regards.

Åukasz Majewski