Date:   Mon, 12 Dec 2016 18:15:28 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Jonathan Cameron <jic23@...nel.org>
Cc:     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

On 12/06/2016 12:12 PM, Bartosz Golaszewski wrote:
> 2016-12-03 10:11 GMT+01:00 Jonathan Cameron <jic23@...nel.org>:
>> On 30/11/16 10:10, Lars-Peter Clausen wrote:
>>> On 11/29/2016 04:35 PM, Bartosz Golaszewski wrote:
>>>> 2016-11-29 16:30 GMT+01:00 Lars-Peter Clausen <lars@...afoo.de>:
>>>>> On 11/29/2016 04:22 PM, Bartosz Golaszewski wrote:
>>>>> [...]
>>>>>> diff --git a/Documentation/devicetree/bindings/iio/misc/iio-regulator.txt b/Documentation/devicetree/bindings/iio/misc/iio-regulator.txt
>>>>>> new file mode 100644
>>>>>> index 0000000..147458f
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/iio/misc/iio-regulator.txt
>>>>>> @@ -0,0 +1,18 @@
>>>>>> +Industrial IO regulator device driver
>>>>>> +-------------------------------------
>>>>>> +
>>>>>> +This document describes the bindings for the iio-regulator - a dummy device
>>>>>> +driver representing a physical regulator within the iio framework.
>>>>>
>>>>> No bindings for drivers, only for hardware. So this wont work.
>>>>>
>>>>
>>>> What about exporting regulator attributes analogous to the one in this
>>>> patch from the iio-core when a *-supply property is specified for a
>>>> node?
>>>
>>> The problem with exposing direct control to the regulator is that it allows
>>> to modify the hardware state without the drivers knowledge. If you
>>> power-cycle a device all previous configuration that has been written to the
>>> device is reset. The device driver needs to be aware of this otherwise its
>>> assumed state and the actual device state can divert which will result in
>>> undefined behavior. Also access to the device will fail unexpectedly when
>>> the regulator is turned off. So I think generally the driver should
>>> explicitly control the regulator, power-up when needed, power-down when not.
>> I agree with what Lars has said.
>>
>> There 'may' be some argument to ultimately have a bridge driver from
>> regulators to IIO.  That would be for cases where the divide between a regulator
>> and a DAC is blurred.  However it would still have to play nicely with the
>> regulator framework and any other devices registered on that regulator.
>> Ultimately the ideal in that case would then be to describe what the DAC is
>> actually being used to do but that's a more complex issue!
>>
>> That doesn't seem to be what you are targeting here.
>>
>> What it sounds like you need is to have the hardware well enough described that
>> the standard runtime power management can disable the regulator just fine when
>> it is not in use.  This may mean improving the power management in the relevant
>> drivers.
>>
>> Jonathan
>>
>> p.s. If ever proposing to do something 'unusual' with a regulator you should
>> bring in the regulator framework maintainers in the cc list.
>>>
>>> - Lars
>>>
>>
> 
> I wrote the initial patch quickly and didn't give it much of a
> thought. Now I realized I completely missed the point and managed to
> confuse everybody - myself included.
> 
> 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.

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