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

[David Lechner]

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.