linux-kernel - Re: Question: How to power-manage UART-attached devices.

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Message-ID: <20120501093559.5c14087d@notabene.brown>
Date:	Tue, 1 May 2012 09:35:59 +1000
From:	NeilBrown <neilb@...e.de>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	linux-serial@...r.kernel.org, linux-pm@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: Question:  How to power-manage UART-attached devices.

On Mon, 30 Apr 2012 23:33:22 +0100 Mark Brown
<broonie@...nsource.wolfsonmicro.com> wrote:

> On Tue, May 01, 2012 at 08:22:09AM +1000, NeilBrown wrote:
> 
> >  The question is how can user-space tell the kernel that these devices are
> >  'inactive'?
> 
> >  I would like to integrate this into Linux in the most  "natural" way that I
> >  can but am having trouble.  My current approach involves using "rfkill" but
> >  that doesn't work very well for reasons that are probably not very relevant
> >  here.  It probably does make sense for powering the GPS antenna, but not
> >  much else.
> 
> The userspace consumer was added for users like this that live entirely
> in userspace.

Hi Mark,
 thanks for the reply.

 I assume you mean REGULATOR_VIRTUAL_CONSUMER (drivers/regulator/virtual.c)?

 The one where the Kconfig entry says:
    This is mainly useful for test purposes.

 That certainly was useful for test purposes but I want to move beyond
 testing.

 One of the purposes of an operating system is to provide useful abstractions
 and hide irrelevant details, so I don't want user-space to have to
 explicitly enable a regulator.
 I could cope with an 'on/off switch' abstraction.  It might then enable a
 regulator. In the case of the GPS device it would need to both enable a
 regulator and toggle a GPIO line.  I really don't want user-space to "know"
 that it has to turn on a regulator and toggle a gpio line...

 So I'm still hoping for something more abstract.

Thanks,
NeilBrown

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