linux-kernel - Re: [lm-sensors] regulator: regulator_get behaviour without CONFIG

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Message-ID: <4BBB6083.2070903@cam.ac.uk>
Date:	Tue, 06 Apr 2010 17:25:39 +0100
From:	Jonathan Cameron <jic23@....ac.uk>
To:	Liam Girdwood <lrg@...mlogic.co.uk>
CC:	Jean Delvare <khali@...ux-fr.org>,
	lm-sensors <lm-sensors@...sensors.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [lm-sensors] regulator: regulator_get behaviour without CONFIG_REGULATOR
 set

On 04/06/10 16:27, Liam Girdwood wrote:
> On Mon, 2010-04-05 at 14:23 +0100, Mark Brown wrote:
>> On Sat, Apr 03, 2010 at 05:37:45PM +0200, Jean Delvare wrote:
>>> On Fri, 2 Apr 2010 21:45:03 +0100, Mark Brown wrote:
>>
>>>> In this case you don't need the if (voltage) check - the code that uses
>>>> supply_uV is going to have to cope with it being set to 0 if the driver
>>>> doesn't just give up, and the enable wants to happen anyway (perhaps
>>>> we've got a switchable supply we can't read the voltage of).  It should
>>>> never make any odds if the notifier never gets called since the supply
>>>> could be invariant.
>>
>>> We still need to check if (voltage) to not overwrite the previous value
>>> of data->supply_uV with 0. We will probably do that as an immediate fix
>>> to the sht15 driver. But yes, the rest doesn't need a condition.
>>
>> I was assuming that there wasn't a previous value since this was in
>> probe(), sorry.
>>
>>> Still, I'd prefer if drivers were just able to check for data->reg ==
>>> NULL and skip the whole thing. Would you apply the following patch?
>>
>>> From: Jean Delvare <khali@...ux-fr.org>
>>> Subject: regulator: Let drivers know when they use the stub API
>>
>>> Have the stub variant of regulator_get() return NULL, so that drivers
>>> can (but still don't have to) handle this case specifically.
>>
>> I guess I'll ack it but I'd be suspicous of driver code which actually
>> makes use of this - there is actual hardware which has the same features
>> as the regulator that gets stubbed in and ought to be handled.  On the
>> other hand, perhaps someone will come up with a good use for it.
>>
>> It also seems a bit odd to return a traditional error value in a success
>> case but it doesn't actually make much difference.
> 
> Thanks, I've applied this with Mark's Ack.
> 
> I suppose this is something we may look into more when we have more
> clients.
Makes sense.  There will probably be quite a few IIO drivers over the next
few months doing much the same as sht15, where the voltage ref for devices
may well be fed by a regulator.  In that case, we may only offer the option
of using an external v_ref if the regulator is available.  Many devices have
an internal regulator to provide it so typically we'll start them up using that
and provide an interface to switch to external regulator if one is available.
I haven't thought through exactly how this will work as yet. I'll cc people in
when this comes up.

Thanks,

Jonathan



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