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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.
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