linux-kernel - Re: [PATCH 2/2] iio: misc: add support for GPIO power switches

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Date:   Fri, 30 Dec 2016 14:05:48 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kevin Hilman <khilman@...libre.com>,
        Patrick Titiano <ptitiano@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Alexandre Courbot <gnurou@...il.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>
Subject: Re: [PATCH 2/2] iio: misc: add support for GPIO power switches

n Thu, Dec 29, 2016 at 5:29 PM, Sebastian Reichel <sre@...nel.org> wrote:
> On Wed, Dec 28, 2016 at 01:50:17PM +0100, Linus Walleij wrote:
>> On Sun, Dec 11, 2016 at 11:21 PM, Bartosz Golaszewski
>> <bgolaszewski@...libre.com> wrote:
>>
>> > Some power-measuring ADCs work together with power load switches which
>> > allow to power-cycle measured devices.
>> >
>> > An example use case would be measuring the power consumption of a
>> > development board during boot using a power monitor such as TI INA226
>> > and power-cycling the board remotely using a TPS229* power switch.
>> >
>> > Add an iio driver for simple GPIO power switches and expose a sysfs
>> > attribute allowing to toggle their state.
>> >
>> > Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
>>
>> I don't get this, isn't this doing the same as
>> drivers/power/reset/gpio-poweroff.c
>> ?
>>
>> With the only difference that the latter uses the standard syscall
>> from pm_power_off to reboot the system instead of some random
>> sysfs file.
>
> As far as I understand it, the TPS229 is used by Barzosz to poweroff
> a remote system. The gpio-poweroff driver is used to poweroff the
> local system.

Thanks yeah I understood this from the context of later patches.

Well if such a property is used it should be the property of the remote
system per se, and the remote system should then also be desribed in
DT, not half-described by dangling references at random nodes.

So this needs to be re-architected to either describe the remote system
in DT and handle it in the kernel, or handle it all from userspace if it
is a one-off non-product thing.

Yours,
Linus Walleij