On Mon, 31 Jul 2023 13:49:46 +0200, Marek Vasut wrote: > > 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. Heh, I also don't recommend that route, either :) (Though, it must be possible to create a sound device with that beep control in theory) > 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). So the question is what's expected from user-space POV. If a more generic control of beep volume is required, e.g. for desktop-like usages, an implementation of sound driver wouldn't be too bad. OTOH, for other specific use-cases, it doesn't matter much in which interface it's implemented, and sysfs could be an easy choice. And, IMO, extending the SND_BEEP with a volume value doesn't sound like a good idea. thanks, Takashi
