linux-kernel - Re: [PATCH] iio: misc: add a generic regulator driver

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Message-ID: <CAMpxmJVpj57s-m_FS58J+QWvu-MnVmaZP-6ECnYHeRVSCfd-Fw@mail.gmail.com>
Date:   Tue, 13 Dec 2016 15:28:22 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Lars-Peter Clausen <lars@...afoo.de>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-iio@...r.kernel.org,
        linux-devicetree <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kevin Hilman <khilman@...libre.com>,
        Patrick Titiano <ptitiano@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] iio: misc: add a generic regulator driver

2016-12-12 18:15 GMT+01:00 Lars-Peter Clausen <lars@...afoo.de>:
> On 12/06/2016 12:12 PM, Bartosz Golaszewski wrote:

[snip!]

>>
>> So the problem we have is not power-cycling the adc - it's
>> power-cycling the device connected to a probe on which there's an adc.
>> What I was trying to do was adding support for the power-switch on
>> baylibre-acme[1] probes.
>>
>> For example: we have a USB probe on which the VBUS signal goes through
>> a power load switch and than through the adc. The adc (in this case
>> ina226) is always powered on, while the fixed regulator I wanted to
>> enable/disable actually drives the power switch to cut/restore power
>> to the connected USB device i.e. there's no real regulator - just a
>> GPIO driving the power switch.
>>
>> A typical use case is measuring the power consumption of development
>> boards[2]. Rebooting them remotely using acme probes is already done,
>> but we're using the obsolete /sys/class/gpio interface.
>>
>> We're already using libiio to read the measured data from the power
>> monitor, that's why we'd like to use the iio framework for
>> power-cycling the devices as well. My question is: would bridging the
>> regulator framework be the right solution? Should we look for
>> something else? Bridge the GPIO framework instead?
>
> I wouldn't necessaries create bridge, but instead just use the GPIO
> framework directly.
>
> We now have the GPIO chardev interface which meant to be used to support
> application specific logic that control the GPIOs, but where you don't want
> to write a kernel driver.
>
> My idea was to add GPIOs and GPIO chips as high level object inside libiio
> that can be accessed through the same context as the IIO devices. Similar to
> the current IIO API you have a API for gpios that allows to enumerate the
> GPIO devices and their pins as well as modify the pin state.
>

+ Linus

While the new GPIO interface would be very convenient - in our case we
could simply name the lines appropriately in the device tree - I'm not
sure this would be the correct approach.

>From this year's ELCE in Berlin I remember Linus suggested during his
talk that it's always better to write a kernel driver. Also: this way
the relevant GPIO lines would not be reserved for exclusive use by
power switches.

Linus - do you have any thoughts/suggestions on that subject?

Best regards,
Bartosz Golaszewski