linux-kernel - Re: [PATCH 1/2] regulators: Add definition of regulator_set_voltage_time() for !CONFIG

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Date:	Wed, 4 Jun 2014 11:16:37 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Mark Brown <broonie@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arvind Chauhan <arvind.chauhan@....com>,
	Eduardo Valentin <edubezval@...il.com>,
	Pavel Machek <pavel@....cz>,
	Liam Girdwood <lgirdwood@...il.com>
Subject: Re: [PATCH 1/2] regulators: Add definition of regulator_set_voltage_time()
 for !CONFIG_REGULATOR

On 3 June 2014 21:18, Mark Brown <broonie@...nel.org> wrote:
> No, as I've explained repeatedly NULL is a perfectly valid regulator and

Okay, its been checked at multiple places already and that's obviously
wrong then.

> that's not going to work reliably.  As I've previously requested please
> think about what happens to cpufreq if we fail to ramp voltages.

Okay, so here is the scenario:

- driver is generic (like cpufreq-cpu0) and some user platforms may have
regulator support and others might not..

- For platforms with regulators support, we _must_ check if the voltage
change is successful or not and fail if regulator_set_voltage() failed.

- But for platforms without regulators support (CONFIG_REGULATOR=n),
regulator_get() will return NULL (a valid regulator though) and
regulator_set_voltage() will fail. Because the platform doesn't care much
about regulators it must go on and change frequency as if nothing
happened.

How can we achieve both these requirements by a generic piece of
code?

The only way I could think of currently is by returning something
special like -ENOSYS from regulator_set_voltage() when
regulators aren't configured in kernel and check return value of
regulator_set_voltage() against this..

This also holds true for regulator_get_voltage() which is returning
-EINVAL currently..

Please share if you have some other solution in mind..
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