From: Guenter Roeck <linux@roeck-us.net>
To: Mark Brown <broonie@kernel.org>
Cc: Wei Ni <wni@nvidia.com>,
khali@linux-fr.org, swarren@wwwdotorg.org,
lm-sensors@lm-sensors.org, linux-tegra@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/2] hwmon: (lm90) Add power control
Date: Mon, 9 Sep 2013 08:50:43 -0700 [thread overview]
Message-ID: <20130909155043.GA18975@roeck-us.net> (raw)
In-Reply-To: <20130909135022.GZ29403@sirena.org.uk>
On Mon, Sep 09, 2013 at 02:50:22PM +0100, Mark Brown wrote:
> 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.
>
Jean will have to ack 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.
Even then it would be unreasonable to enforce such a delay for every instance
of this driver, even if the regulator is a dummy one and/or has been enabled
already. Many if not almost all users of the driver work just fine as-is,
without additional enforced delay (and, for that matter, without regulator ;).
If there is a delay, it would have to be optional: Only wait if the regulator
was really turned on by the call and not already active. I don't know if the
regulator subsystem has this capability; if not, maybe it should.
On a higher level, I wonder if such functionality should be added in the i2c
subsystem and not in i2c client drivers. Has anyone thought about this ?
Guenter
next prev parent reply other threads:[~2013-09-09 15:50 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-09 10:29 [PATCH v3 0/2] Add power control for lm90 Wei Ni
2013-09-09 10:29 ` [PATCH v3 1/2] hwmon: (lm90) Add power control Wei Ni
2013-09-09 11:12 ` Mark Brown
2013-09-09 11:34 ` Guenter Roeck
2013-09-09 13:50 ` Mark Brown
2013-09-09 15:50 ` Guenter Roeck [this message]
2013-09-09 16:02 ` Mark Brown
2013-09-09 16:17 ` Guenter Roeck
2013-09-09 20:39 ` Mark Brown
2013-09-10 4:05 ` Wei Ni
2013-09-10 4:50 ` Guenter Roeck
2013-09-10 5:39 ` Wei Ni
2013-09-10 5:54 ` Guenter Roeck
2013-09-10 6:30 ` Wei Ni
2013-09-10 10:13 ` Mark Brown
2013-09-10 11:29 ` Wei Ni
2013-09-10 12:11 ` Mark Brown
2013-09-11 9:40 ` Wei Ni
2013-09-10 3:22 ` Wei Ni
2013-09-10 3:36 ` Guenter Roeck
2013-09-10 3:40 ` Stephen Warren
2013-09-10 3:53 ` Guenter Roeck
2013-09-10 4:12 ` Wei Ni
2013-09-10 4:13 ` Stephen Warren
2013-09-10 4:44 ` Guenter Roeck
2013-09-10 10:09 ` Mark Brown
2013-09-10 15:07 ` Stephen Warren
2013-09-10 17:04 ` Mark Brown
2013-09-10 17:44 ` Stephen Warren
2013-09-10 18:07 ` Guenter Roeck
2013-09-10 18:18 ` Mark Brown
2013-09-10 18:37 ` Stephen Warren
2013-09-10 18:52 ` Mark Brown
2013-09-11 11:35 ` Wei Ni
2013-09-10 17:05 ` Mark Brown
2013-09-09 10:29 ` [PATCH v3 2/2] Documentation: dt: hwmon: add OF document for LM90 Wei Ni
2013-09-09 10:52 ` Guenter Roeck
2013-09-09 22:14 ` Stephen Warren
2013-09-10 4:25 ` Wei Ni
2013-09-09 10:57 ` Ramkumar Ramachandra
2013-09-10 4:35 ` Wei Ni
2013-09-10 4:36 ` Wei Ni
2013-09-09 22:15 ` Stephen Warren
2013-09-09 22:23 ` Guenter Roeck
2013-09-10 4:25 ` Wei Ni
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