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

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Date:	Wed, 25 Nov 2015 11:50:30 +0200
From:	Adriana Reus <adriana.reus@...el.com>
To:	Rob Herring <robh@...nel.org>
Cc:	jic23@...nel.org, 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 25.11.2015 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.
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