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

From: Åukasz Majewski
Date: Tue Oct 03 2017 - 18:52:38 EST

Hi Dmitry,

Hi Åukasz,

On Tue, Oct 3, 2017 at 9:58 AM, Åukasz Majewski <l.majewski@xxxxxxxxx> wrote:
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
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 :-)

Please start from the beginning: it is not quite clear why you want
the touchscreen to be re-enumerated.

The above setup generally works.

However, from time to time I do encounter some HID multi-touch driver initialization errors, which render the touchscreen unusable - e.g:

usb 1-1: input irq status -75 received
usb 1-1: reset low-speed USB device number 2 using ci_hdrc
expected 16 bytes, got -1


hid-generic 0003:19E2:2533.0002: unknown main item tag 0x0
hid-generic 0003:19E2:2533.0002: unknown main item tag 0x0
hid-generic 0003:19E2:2533.0002: unbalanced collection at end of report description
hid-generic: probe of 0003:19E2:2533.0002 failed with error -22

I've added 100 ms settle time for the VBUS regulator, but I'm not sure if it will fix this issue (I'm going to inspect VBUS voltage with oscilloscope).

Since I do have above errors, I thought that it would be feasible to have a "mean" to re-set VBUS voltage and force enumeration of the device.

I'm quite curious how USB connected touchscreens are controlled with USB's VBUS not accessible from user-space out of the box?


Best regards.

Åukasz Majewski