Message-ID: <c028b2fc-7ed1-772c-82e3-b98a25f58ffb@kernel.org>
Date:   Sat, 10 Dec 2016 18:17:40 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        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 06/12/16 11:12, 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?
Definitely doesn't fit inside standard scope of IIO - though I can see
why you were thinking along these lines.

Mark Brown, any thoughts?

Effectively we are are looking at something that (in general form) might
be the equivalent of controlling a lab bench supply... So regulators
at the edge of the known world, with no visibility of what lies beyond.
> 
> Best regards,
> Bartosz Golaszewski
> 
> [1] http://baylibre.com/acme/
> [2] https://github.com/BayLibre/POWERCI
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