linux-kernel - Re: [PATCH] regulator: Provide optional dummy regulator for consumers

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Message-Id: <10B19BD9-34B8-4E0E-9737-09141A37BD00@opensource.wolfsonmicro.com>
Date:	Fri, 12 Feb 2010 23:26:20 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Grazvydas Ignotas <notasas@...il.com>
Cc:	Liam Girdwood <lrg@...mlogic.co.uk>,
	Mike Rapoport <mike@...pulab.co.il>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] regulator: Provide optional dummy regulator for consumers

On 12 Feb 2010, at 23:01, Grazvydas Ignotas <notasas@...il.com> wrote:

> On Fri, Feb 12, 2010 at 12:18 PM, Mark Brown
> <broonie@...nsource.wolfsonmicro.com> wrote:
>> In order to ease transitions with drivers are boards start using  
>> regulators
>> provide an option to cause all regulator_get() calls to succeed,  
>> with a
>> dummy always on regulator being supplied where one has not been  
>> configured.
>> A warning is printed whenever the dummy regulator is used to aid  
>> system
>> development.
>>
>> This regulator does not implement any regulator operations but will  
>> allow
>> simple consumers which only do enable() and disable() calls to run.  
>> It
>> is kept separate from the fixed voltage regulator to avoid Kconfig
>> confusion on the part of users when it is extended to allow boards to
>> explicitly use the dummy regulator to simplify cases where the  
>> majority
>> of supplies are from fixed regulators without software control.
>>
>> This option is currently only effective for systems which do not  
>> specify
>> full constriants. If required an override could also be provided to  
>> allow
>> these systems to use the dummy regulator, though it is likely that
>> unconfigured supplies on such systems will lead to error due to
>> regulators being powered down more aggressively when not in use.
>>
>> Signed-off-by: Mark Brown <broonie@...nsource.wolfsonmicro.com>
>> ---
>>
>
> hm, tried intentionally nuking regulator setup on my board to test
> dummy and drivers started failing on regulator_enable() with -1
> (EPERM?). Looks like dummy doesn't have constraints defined, so not
> much use of this if _enable() is failing anyway.

Hrmpf. That was working for me - are you running the latest regulator  
code? There was a bug where it was requiring CHANGE_STATUS even if the  
regulator is always on, which isn't sensible since there is no  
possibility of actually changing the status. It should now only be  
checking for permission to change status if it would actually do so.  
There was also a patch yesterday to make regulators that don't define  
an is_enabled() report as enabled.

> BTW, drivers/mmc/host/omap_hsmmc.c has quite a lot of logic related to
> vcc_aux being available or not (vcc_aux is typically used to power
> some MMC pins and is unused on devices with SD cards, like pandora). I
> wonder if it may cause some functionality change there.

Yeah, quite possibly. This sort of stuff is one of the reasons it's  
much nicer to specify full constraints where possible; it allows  
drivers that can have missing supplies to handle that.
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