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

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Date:   Tue, 3 Oct 2017 12:16:41 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Łukasz Majewski <l.majewski@...ess.pl>
Cc:     "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [Regulator] Request for clarification - GPIO controlled
 regulator, USB VBUS,

Hi Łukasz,

On Tue, Oct 3, 2017 at 9:58 AM, Łukasz Majewski <l.majewski@...ess.pl> 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):
> https://patchwork.ozlabs.org/patch/374912/
> https://lkml.org/lkml/2014/7/30/357
>
> 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:
> http://elixir.free-electrons.com/linux/latest/source/drivers/usb/phy/phy-fsl-usb.c
>
> (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.

Thanks.

-- 
Dmitry