linux-kernel - Re: [PATCH v3 1/2] hwmon: (lm90) Add power control

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Date:	Mon, 9 Sep 2013 14:50:22 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Wei Ni <wni@...dia.com>, khali@...ux-fr.org, swarren@...dotorg.org,
	lm-sensors@...sensors.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] hwmon: (lm90) Add power control

On Mon, Sep 09, 2013 at 04:34:43AM -0700, Guenter Roeck wrote:
> On 09/09/2013 04:12 AM, Mark Brown wrote:
> >On Mon, Sep 09, 2013 at 06:29:11PM +0800, Wei Ni wrote:

> >This doesn't look good, it is going to ignore actual errors - I *really*
> >doubt that vcc is optional, it looks like it's the main power supply for
> >the device.  You should use normal regulator_get(), _optional() is for
> >supplies which could physically not be provided in a system (eg, if the
> >device can generate them internally if required).

> Then he'll have to make sure that all devicetree files in the system
> contain references to this regulator.

Or get the patches applied on top of the code that'll be going in this
cycle implementing get_optional() properly - when that's done the
default will be to provide a dummy supply for regulator_get().  If you
ack the patch I'd be happy to carry it.

> >Also do you really need 25ms after power on?

> I had not noticed, but I recommend to reject the patch because of it.
> If we add 25ms delay to each driver, booting the system will take as
> long as booting windows. If enabling the regulator needs time, the
> regulator subsystem should do it.

And indeed it does this (well, it does whatever the driver says in terms
of delay).  However it is possible that the lm90 needs this time for
itself - if it's doing some sort of initialisation or callibration
sequence then that'll happen after the supplies come up.  25ms did seem
rather long, especially for such simple devices, but it's not beyond the
bounds of possibility.

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