On 7/31/23 08:21, Takashi Iwai wrote:
On Mon, 31 Jul 2023 07:36:38 +0200,
Dmitry Torokhov wrote:
On Sat, May 13, 2023 at 11:02:30PM +0200, Marek Vasut wrote:
On 5/13/23 03:51, Marek Vasut wrote:
On 5/13/23 03:12, Jeff LaBundy wrote:
Hi Marek,
Hi,
On Fri, May 12, 2023 at 08:55:51PM +0200, Marek Vasut wrote:
The PWM beeper volume can be controlled by adjusting the PWM duty cycle,
expose volume setting via sysfs, so users can make the beeper quieter.
This patch adds sysfs attribute 'volume' in range 0..50000, i.e. from 0
to 50% in 1/1000th of percent steps, this resolution should be
sufficient.
The reason for 50000 cap on volume or PWM duty cycle is because
duty cycle
above 50% again reduces the loudness, the PWM wave form is inverted wave
form of the one for duty cycle below 50% and the beeper gets quieter the
closer the setting is to 100% . Hence, 50% cap where the wave
form yields
the loudest result.
Signed-off-by: Marek Vasut <marex@xxxxxxx>
---
An alternative option would be to extend the userspace input
ABI, e.g. by
using SND_TONE top 16bits to encode the duty cycle in 0..50000
range, and
bottom 16bit to encode the existing frequency in Hz . Since frequency in
Hz is likely to be below some 25 kHz for audible bell, this fits
in 16bits
just fine. Thoughts ?
---
Thanks for the patch; this seems like a useful feature.
My first thought is that 50000 seems like an oddly specific limit to
impose
upon user space. Ideally, user space need not even care that the
beeper is
implemented via PWM and why 50000 is significant.
Instead, what about accepting 0..255 as the LED subsystem does for
brightness,
then map these values to 0..50000 internally? In fact, the leds-pwm
driver
does something similar.
The pwm_set_relative_duty_cycle() function can map whatever range to
whatever other range of the PWM already, so that's not an issues here.
It seems to me the 0..127 or 0..255 range is a bit too limiting . I
think even for the LEDs the reason for that limit is legacy design, but
here I might be wrong.
I'm also curious as to whether this function should be a rogue sysfs
control
limited to this driver, or a generic operation in input. For
example, input
already allows user space to specify the magnitude of an FF effect;
perhaps
something similar is warranted here?
See the "An alternative ..." part above, I was wondering about this too,
whether this can be added into the input ABI, but I am somewhat
reluctant to fiddle with the ABI.
Thinking about this further, we could try and add some
EV_SND SND_TONE_WITH_VOLUME
to avoid overloading EV_SND SND_TONE , and at the same time allow the user
to set both frequency and volume for the tone without any race condition
between the two.
The EV_SND SND_TONE_WITH_VOLUME would still take one 32bit parameter, except
this time the parameter 16 LSbits would be the frequency and 16 MSbits would
be the volume.
But again, here I would like input from the maintainers.
Beeper was supposed to be an extremely simple device with minimal
controls. I wonder if there is need for volume controls, etc, etc are we
not better moving it over to the sound subsystem. We already have:
sound/drivers/pcsp/pcsp.c
and
sound/pci/hda/hda_beep.c
there, can we have other "advanced" beepers there as well? Adding sound
maintainers to CC...
I don't mind it put to sound/*. But, note that pcsp.c you pointed in
the above is a PCM tone generator driver with a PC beep device, and it
provides the normal SND_BEEP input only for compatibility.
Indeed there have been already many sound drivers providing the beep
capability, and they bind with the input device using SND_BEEP. And,
for the beep volume, "Beep Playback Volume" mixer control is provided,
too.
Uh, I don't need a full sound device to emit beeps, that's not even
possible with this hardware. I only need to control loudness of the
beeper that is controlled by PWM output. That's why I am trying to
extend the pwm-beeper driver, which seems the best fit for such a
device, it is only missing this one feature (loudness control).
