linux-kernel - Re: Regulator supplies when using Device Tree

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Date:	Wed, 28 Mar 2012 12:19:45 -0700
From:	Michael Bohan <mbohan@...eaurora.org>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
CC:	rnayak@...com, lrg@...com, LKML <linux-kernel@...r.kernel.org>,
	linux-arm-msm@...r.kernel.org
Subject: Re: Regulator supplies when using Device Tree

On 3/28/2012 3:09 AM, Mark Brown wrote:
> On Tue, Mar 27, 2012 at 06:38:30PM -0700, Michael Bohan wrote:
>> the answer is that we should invent another binding to portray the
>> name of the supply the driver should be checking against. But then
>> it would seem silly to have two bindings that pertain to supply
>> names.
>
> Absolutely not, that would be broken.  The whole point here is that
> supplies of all kinds are always requested with the name the chip uses
> for the supply.

Let's consider an example with two regulators:

regulator@0 {
   compatible = "ldo_driver";
   foo-supply = <&smps1>;
};

regulator@1 {
   compatible = "ldo_driver";
};

How do we write a single regulator driver that supports both of these 
regulator devices?

Within the regulator driver, we currently have to do an 
of_get_property(of_node, "foo-supply", NULL) to determine whether the 
device has a supply, and thus whether we should assign 
rdesc->supply_name to "foo" or not when calling regulator_register(). Is 
there a better way to do this? If we don't do this check for the case 
where a device does not have a supply specified in the Device Tree, then 
regulator_register() will fail.

Before Device Tree, regulators could get their supply names directly 
from the board file like so:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=Documentation/power/regulator/machine.txt;h=ce63af0a8e35ecab32e2f326d13a9a2b33b62909;hb=refs/heads/master#l67

Thus the regulator driver was never concerned about the specifics of a 
supply name. And if the supply name was not specified, then the 
regulator_register() would happily succeed without any checks in the 
driver.

Thanks,
Mike

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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