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... Thanks. -- Dmitry
