linux-kernel - Re: [PATCH v3 0/3] input: pwm-beeper: add feature to set volume level

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Date:   Fri, 17 Feb 2017 11:01:47 +0100
From:   Frieder Schrempf <frieder.schrempf@...eet.de>
To:     David Lechner <david@...hnology.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:     <robh@...nel.org>, <pawel.moll@....com>,
        <ijc+devicetree@...lion.org.uk>, <galak@...eaurora.org>,
        <luis@...ethencourt.com>, <linux-input@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/3] input: pwm-beeper: add feature to set volume level

On 16.02.2017 22:44, David Lechner wrote:
> On 02/16/2017 03:15 PM, Frieder Schrempf wrote:
>> Hello David,
>>
>> On 20.01.2017 20:11, David Lechner wrote:
>>> 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.
>>
>> I have just send v4.
>>>
>>> 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?
>>
>> An alsa mixer control for the pwm-beeper volume sounds nice, but
>> unfortunately I have no idea how one would implement this, or if this is
>> even possible.
>>>
>
>
> I know it is possible because I have done it. ;-)
>
> https://github.com/ev3dev/lego-linux-drivers/blob/master/evb/evb_sound.c
>
> The driver in the link above does PCM playback using PWM. But, it also
> included an input device similar to pwm-beeper and it includes an ALSA
> volume control specifically for the beeper.

Aha, thanks. Doesn't look too complicated. I think I will play with this 
a bit, when I have time. So maybe the sysfs volume control can be 
replaced with a proper volume mixer control at some point.