linux-kernel - Re: [PATCH 2/5] Documentation: devicetree: Add property for controlling power saving mode for the us5182 als sensor

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Message-ID: <565B0D78.6010707@kernel.org>
Date:	Sun, 29 Nov 2015 14:36:40 +0000
From:	Jonathan Cameron <jic23@...nel.org>
To:	Rob Herring <robh@...nel.org>,
	Adriana Reus <adriana.reus@...el.com>
Cc:	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	pawel.moll@....com, pmeerw@...erw.net, lars@...afoo.de
Subject: Re: [PATCH 2/5] Documentation: devicetree: Add property for
 controlling power saving mode for the us5182 als sensor

On 25/11/15 23:55, Rob Herring wrote:
> On Wed, Nov 25, 2015 at 11:50:30AM +0200, Adriana Reus wrote:
>>
>>
>> On 25.11.2015 02:01, Rob Herring wrote:
>>> On Tue, Nov 24, 2015 at 12:59:49PM +0200, Adriana Reus wrote:
>>>> Add a property to allow changing the default power-saving mode.
>>>> By default, at read raw the chip will activate and provide
>>>> one measurent, then it will shut itself down. However, the
>>>> chip can also work in "continuous" mode which may be more reliable
>>>> but is also more power consuming.
>>>>
>>>> Signed-off-by: Adriana Reus <adriana.reus@...el.com>
>>>> ---
>>>>  Documentation/devicetree/bindings/iio/light/us5182d.txt | 11 +++++++++++
>>>>  1 file changed, 11 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/iio/light/us5182d.txt b/Documentation/devicetree/bindings/iio/light/us5182d.txt
>>>> index 6f0a530..a619799 100644
>>>> --- a/Documentation/devicetree/bindings/iio/light/us5182d.txt
>>>> +++ b/Documentation/devicetree/bindings/iio/light/us5182d.txt
>>>> @@ -7,13 +7,24 @@ Required properties:
>>>>  Optional properties:
>>>>  - upisemi,glass-coef: glass attenuation factor - compensation factor of
>>>>                        resolution 1000 for material transmittance.
>>>> +
>>>>  - upisemi,dark-ths: array of 8 elements containing 16-bit thresholds (adc
>>>>                      counts) corresponding to every scale.
>>>> +
>>>>  - upisemi,upper-dark-gain: 8-bit dark gain compensation factor(4 int and 4
>>>>                             fractional bits - Q4.4) applied when light > threshold
>>>> +
>>>>  - upisemi,lower-dark-gain: 8-bit dark gain compensation factor(4 int and 4
>>>>                             fractional bits - Q4.4) applied when light < threshold
>>>>
>>>> +- upisemi,continuous: This chip has two power modes: one-shot (chip takes one
>>>> +                      measurement and then shuts itself down) and continuous (
>>>> +                      chip takes continuous measurements). The one-shot mode is
>>>> +                      more power-friendly but the continuous mode may be more
>>>> +                      reliable. If this property is specified the continuous
>>>> +                      mode will be used instead of the default one-shot one for
>>>> +                      raw reads.
>>>
>>> I could imagine an OS may want to decide this on its own or use a
>>> mixture of the modes.
>>>
>>> Rob
>>>
>>
>> There is no possibility of mixing them up (at the same time), so for example
>> proximity cannot work in one mode and als the other.
>>
>> The one-shot mode can only be used for raw reads (for example when
>> user-space polls in_[proximity|light]_raw). If user-space wants to enable
>> events (activate interrupts when certain thresholds are met - patch 5 of the
>> series), then the chip has to switch to continuous nonetheless because it
>> needs to be active all the time. So one work-flow scenario would be:
>>
>> Consumer1 starts polling the raw interface - default_mode
>> Consumer2 activates events - continuous mode
>> Consumer2 deactivates events - back to default_mode
>>
>> The only choice here is the default mode for raw reads, it currently is
>> one-shot, this patch allows for continuous to be used if preferred.
> 
> Okay, then:
> 
> Acked-by: Rob Herring <robh@...nel.org>
Applied to the togreg branch of iio.git - initially pushed out as testing.

Thanks,

Jonathan
> 
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