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Re: [PATCH v2 2/3] input: pwm-beeper: add documentation for volume devicetree bindings

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  Re: [PATCH v2 2/3] input: pwm-beeper: add documentation for volume  devicetree bindings Frieder Schrempf <frieder.schrempf@exceet.de> - 2017-01-19 16:00 +0100
    [PATCH v3 0/3] input: pwm-beeper: add feature to set volume level Frieder Schrempf <frieder.schrempf@exceet.de> - 2017-01-19 16:30 +0100
      Re: [PATCH v3 0/3] input: pwm-beeper: add feature to set volume level Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2017-01-19 22:50 +0100
        Re: [PATCH v3 0/3] input: pwm-beeper: add feature to set volume level David Lechner <david@lechnology.com> - 2017-01-20 20:20 +0100

#1562803 — Re: [PATCH v2 2/3] input: pwm-beeper: add documentation for volume devicetree bindings

On 11.10.2016 15:39, Rob Herring wrote:
> On Tue, Oct 11, 2016 at 3:17 AM, Schrempf Frieder
> <frieder.schrempf@exceet.de> wrote:
>> On 10.10.2016 17:20, Rob Herring wrote:
>>> On Fri, Oct 07, 2016 at 09:08:17AM +0000, Schrempf Frieder wrote:
>>>> This patch adds the documentation for the devicetree bindings to set
>>>> the volume levels.
>>>>
>>>> Signed-off-by: Frieder Schrempf <frieder.schrempf@exceet.de>
>>>> ---
>>>> Changes in v2:
>>>>  - split into 3 separate patches
>>>>  - make volume properties optional
>>>>
>>>>  .../devicetree/bindings/input/pwm-beeper.txt       | 22 ++++++++++++++++++++++
>>>>  1 file changed, 22 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/input/pwm-beeper.txt b/Documentation/devicetree/bindings/input/pwm-beeper.txt
>>>> index be332ae..6d8ba4e 100644
>>>> --- a/Documentation/devicetree/bindings/input/pwm-beeper.txt
>>>> +++ b/Documentation/devicetree/bindings/input/pwm-beeper.txt
>>>> @@ -5,3 +5,25 @@ Registers a PWM device as beeper.
>>>>  Required properties:
>>>>  - compatible: should be "pwm-beeper"
>>>>  - pwms: phandle to the physical PWM device
>>>> +
>>>> +Optional properties:
>>>> +- 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).
>>>> +      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).
>>>
>>> What does the index correspond to? The linear volume?
>>
>> In most cases users probably need linear volume levels (e.g. 0%, 25%,
>> 50%, 75%, 100%) and in this case the index would indeed correspond to
>> the linear perceived volume.
>>
>> But also non-linear relations are possible (e.g. 0%, 20%, 100%), if the
>> user needs for example "mute", "low", "high" as volume levels.
>
> Exclude off/mute and this is still linear. Also, the user exposed
> levels could be a subset of the defined h/w levels. That should be
> independent of DT.

Ok
>
>> The linearization (defining the corresponding duty cycle for each index)
>> depends on the beeper and the perception of the user.
>
> This has to be a consistent interface across h/w to have a userspace
> that can work across h/w. For that, you have to define the binding as
> linear. Of course, it's all measured by perception and not completely
> accurate which is fine.

I see. I will resend and change the description to make clear, that the
volume-levels property is meant to specify linear volume levels.
>
>> For the example array definition below, I tried different duty cycles
>> and found values of 0.8%, 2%, 4%, 50% to be approximately correspondent
>> to perceived volume levels of 25%, 50%, 75%, 100% in my case.
>>
>>>
>>>> +- 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.
>
> Also, drop this. Not relevant to the binding.

Ok, I will drop this.
>
> Rob
>

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#1562825 — [PATCH v3 0/3] input: pwm-beeper: add feature to set volume level

Make the driver accept switching volume levels via sysfs.
This can be helpful if the beep/bell sound intensity needs
to be adapted to the environment of the device.

The number of volume levels available and their values can
be specified via device tree (similar to pwm-backlight).

The volume adjustment is done by changing the duty cycle of
the pwm signal.

Changes in v3:
 - update date
 - change description of volume-levels to be used for linear levels

Frieder Schrempf (3):
  input: pwm-beeper: add feature to set volume via sysfs
  input: pwm-beeper: add documentation for volume devicetree bindings
  input: pwm-beeper: add devicetree bindings to set volume levels

 .../ABI/testing/sysfs-class-input-pwm-beeper       |  17 +++
 .../devicetree/bindings/input/pwm-beeper.txt       |  20 ++++
 drivers/input/misc/pwm-beeper.c                    | 116 ++++++++++++++++++++-
 3 files changed, 151 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-input-pwm-beeper

-- 
2.7.4

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#1563115 — Re: [PATCH v3 0/3] input: pwm-beeper: add feature to set volume level

On Thu, Jan 19, 2017 at 04:24:07PM +0100, Frieder Schrempf wrote:
> Make the driver accept switching volume levels via sysfs.
> This can be helpful if the beep/bell sound intensity needs
> to be adapted to the environment of the device.
> 
> The number of volume levels available and their values can
> be specified via device tree (similar to pwm-backlight).
> 
> The volume adjustment is done by changing the duty cycle of
> the pwm signal.

I wonder how this all will mesh up with beepers that have dedicated
amplifiers (support is being added by David Lechner).

Thanks.

-- 
Dmitry

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#1563874 — Re: [PATCH v3 0/3] input: pwm-beeper: add feature to set volume level

On 01/19/2017 03:37 PM, Dmitry Torokhov wrote:
> On Thu, Jan 19, 2017 at 04:24:07PM +0100, Frieder Schrempf wrote:
>> Make the driver accept switching volume levels via sysfs.
>> This can be helpful if the beep/bell sound intensity needs
>> to be adapted to the environment of the device.
>>
>> The number of volume levels available and their values can
>> be specified via device tree (similar to pwm-backlight).
>>
>> The volume adjustment is done by changing the duty cycle of
>> the pwm signal.
>
> I wonder how this all will mesh up with beepers that have dedicated
> amplifiers (support is being added by David Lechner).

This will work very well with it. I fact, it is a feature I would like 
to have but I was not sure about a good way to implement it. Please Cc: 
me on future revisions of this series and I will be glad to test it.

One thing that would be nice would be for a more generic way to change 
the volume from userspace. Having a sysfs attribute on the platform 
device will work, but it requires very specific knowledge from any 
userspace program that wants to control the volume. Would it be possible 
to add an alsa mixer volume control or something like that?

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