linux-kernel - Re: [PATCH v3 1/2] hwmon: (lm90) Add power control

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Date:	Tue, 10 Sep 2013 12:37:47 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mark Brown <broonie@...nel.org>
CC:	Guenter Roeck <linux@...ck-us.net>, Wei Ni <wni@...dia.com>,
	"khali@...ux-fr.org" <khali@...ux-fr.org>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] hwmon: (lm90) Add power control

On 09/10/2013 12:18 PM, Mark Brown wrote:
> On Tue, Sep 10, 2013 at 11:44:05AM -0600, Stephen Warren wrote:
> 
>> OK, so I believe you're saying that the case of a chip with just
>> a single power source, which absolutely must be present in HW for
>> the chip to be powered, isn't appropriate for
>> regulator_get_optional(). Something must always define a
>> regulator for that power source, even if there is no external SW
>> control over that power source.
> 
> Well, it really should be mandatory - personally I don't think
> it's sensible to add off-SoC chips without defining their
> regulators, it's more trouble than it's worth to have to add them
> later for all the time it takes to define the bindings.  In IETF
> terms it's a should.
> 
>> We either allow the regulator to be optional (since SW control
>> over the regulator is optional), or go back to every board file
>> and DT and add a dummy regulator in (which then breaks DT ABI,
>> and even ignoring that is a pain).
> 
> The whole point of the way I'm changing the dummy support is to
> allow us to gracefully cope with errors here so there's no
> mandatory update even though strictly there should be one.

OK, so for the DT binding we should make vcc-supply a required
property, yet the driver will still work OK if that property just
happens to be missing (or e.g. when instantiated from a board file,
and there's no regulator).
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