linux-kernel - Re: [PATCH 1/1] input: pwm-beeper: add feature to set volume via sysfs

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Date:   Fri, 7 Oct 2016 09:00:53 +0000
From:   Schrempf Frieder <frieder.schrempf@...eet.de>
To:     Rob Herring <robh@...nel.org>
CC:     "dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>,
        "pawel.moll@....com" <pawel.moll@....com>,
        "ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
        "galak@...eaurora.org" <galak@...eaurora.org>,
        "luis@...ethencourt.com" <luis@...ethencourt.com>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] input: pwm-beeper: add feature to set volume via
 sysfs

Thank you Rob for looking at my first kernel contribution.
I come back to it now, as I had some time to process your comments.

On 11.04.2016 17:21, Rob Herring wrote:
> On Thu, Apr 07, 2016 at 03:58:40PM +0000, Schrempf Frieder wrote:
>> Make the driver accept different volume levels via sysfs.
>> This can be helpful if the beep/bell sound intensity needs
>> to be adapted to the environment of the device.
>
> It is preferred that bindings be a separate patch. Also, this is 2
> independent features: the sysfs interface and DT properties. So that is
> probably 3 patches.
>
> Also, sysfs interfaces are supposed to be documented.

I have splitted this into 3 patches and will send them soon as v2.
I also added documentation for the sysfs interface.

>
>>
>> The number of volume levels available and their values can
>> be specified via device tree (similar to pwm-backlight).
>>
>> This patch was tested with linux-imx 3.10.17 and was
>> applied to current mainline without any changes.
>
> You need to test with something not 3 years old...

I tested the v2 patches with Linux 4.7.4 now.

>
>>
>> Signed-off-by: Frieder Schrempf <frieder.schrempf@...eet.de>
>> ---
>>  .../devicetree/bindings/input/pwm-beeper.txt    |  20 ++++
>>  drivers/input/misc/pwm-beeper.c                 | 109 ++++++++++++++++++-
>>  2 files changed, 126 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/input/pwm-beeper.txt b/Documentation/devicetree/bindings/input/pwm-beeper.txt
>> index be332ae..153cd3f 100644
>> --- a/Documentation/devicetree/bindings/input/pwm-beeper.txt
>> +++ b/Documentation/devicetree/bindings/input/pwm-beeper.txt
>> @@ -5,3 +5,23 @@ Registers a PWM device as beeper.
>>  Required properties:
>>  - compatible: should be "pwm-beeper"
>>  - pwms: phandle to the physical PWM device
>> +- volume-levels: Array of distinct volume levels. These need to be in the
>> +      range of 0 to 500, while 0 means 0% duty cycle (mute) and 500 means
>> +      50% duty cycle (max volume).
>
> Where does the scale of 0-500 come from? It is tenth of a percent?

I used tenth of a percent because this is needed to define low volume 
levels with pwm duty cycles in the range of <1%.
This is necessary because of the highly non-linear relation between duty 
cycle and actual perceived volume.

The upper limit of 500 therefore results from 50% being the duty cycle 
with maximum volume.

>
> How many array entries?

The array size and therefore the number of volume levels is dynamic and 
only defined by the number of entries in the volume-levels property.

>
>> +      Please note that the actual volume of most beepers is highly
>> +      non-linear, which means that low volume levels are probably somewhere
>> +      in the range of 1 to 30 (0.1-3% duty cycle).
>> +- default-volume-level: the default volume level (index into the
>> +      array defined by the "volume-levels" property)
>> +
>> +The volume level can be set via sysfs under /sys/class/input/inputX/volume.
>> +The maximum volume level index can be read from /sys/class/input/inputX/max_volume_level.
>> +
>> +Example:
>> +
>> +	pwm-beeper {
>> +		compatible = "pwm-beeper";
>> +		pwms = <&pwm4 0 5000>;
>> +		volume-levels = <0 8 20 40 500>;
>> +		default-volume-level = <4>;
>> +	};