linux-kernel - Re: Question about fixed regulator DT properties

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Message-ID: <547630AD.1010108@mentor.com>
Date:	Wed, 26 Nov 2014 21:57:33 +0200
From:	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:	Mark Brown <broonie@...nel.org>
CC:	Liam Girdwood <lgirdwood@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: Question about fixed regulator DT properties

On 26.11.2014 21:20, Mark Brown wrote:
> On Wed, Nov 26, 2014 at 09:13:50PM +0200, Vladimir Zapolskiy wrote:
> 
>> If I want to enable a fixed regulator (not controlled by
>> bootloader/firmware) by Linux on boot or when fixed.ko module is bound,
>> shall I specify the same "regulator-boot-on" property? At least this is
>> the practical way to enable a fixed and/or gpio regulator right now, but
>> is it correct?
> 
> It depends what you're trying to accomplish by doing this.

If "regulator-boot-on" is specified and the regulator is enabled by
bootloader/firmware, then the kernel re-enables it.

If "regulator-boot-on" is specified and the regulator is untouched by
bootloader/firmware, then the kernel simply enables it.

As far as I understand the latter side-effect is exploited on quite many
ARM boards, when there is no defined regulator consumer, but I agree
that it looks hackish. My assumption is that probably fixed regulator
logic around "regulator-boot-on" property should be changed, so that the
kernel will not attempt to physically re-enable/enable the
"regulator-boot-on" regulator at all, then misusage of the property
should gone forced by necessity of finding a proper regulator consumer.

>> Or should the regulator always be enabled externally (assuming
>> "regulator-always-on" is omitted) after registration independently on
>> "regulator-boot-on" property?
> 
> Best practice is that there should be a consumer which keeps the
> regulator enabled whenever it is required.  There should normally be
> little use for boot-on, it's mostly there to ease handover from the
> bootloader in cases where we can't read the hardware state - if you're
> not sure if you should use it the chances are you shouldn't.
> 

Right, thank you for explanation.

--
With best wishes,
Vladimir
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