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

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Date:   Thu, 16 Feb 2017 22:15:29 +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

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.
>