linux-kernel - Re: [PATCH v1 4/7] iio: st_sensors: Call st_sensors_power

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Message-ID: <CAHp75Vf=r-rhuzx-DXHcY1xB=t4HP3wNdYAWH1buvqBvTteJ0Q@mail.gmail.com>
Date:   Sun, 18 Apr 2021 16:36:17 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Gaëtan André <rvlander@...tanandre.eu>,
        Nuno Sá <nuno.sa@...log.com>,
        Denis Ciocca <denis.ciocca@...com>,
        linux-iio <linux-iio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v1 4/7] iio: st_sensors: Call st_sensors_power_enable()
 from bus drivers

On Sun, Apr 18, 2021 at 1:54 PM Jonathan Cameron <jic23@...nel.org> wrote:
> On Wed, 14 Apr 2021 22:54:51 +0300
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
>
> > In case we would initialize two IIO devices from one physical device,
> > we shouldn't have a clash on regulators. That's why move
> > st_sensors_power_enable() call from core to bus drivers.
>
> Why is this a problem?

You can't have two regulators of the same name on the same device.
IIRC the regulator framework produces a good splat for this.

>  The two instances would double up and both get +
> enable + disable the regulators.  However, that shouldn't matter as
> they are reference counted anyway.
>
> Perhaps an example?  Even in patch 6 I can only see that it is wasteful
> to do it twice, rather than wrong as such.

Believe me, I would like to avoid that, but it seems a limitation of
the regulator framework. It simply produces a splat. I'll try to
reproduce it again (because this series started like a couple of years
ago, just eventually I found a time to clean up and submit) and will
tell you how it is going.


-- 
With Best Regards,
Andy Shevchenko