Hi Marek and Traut, On Mon, May 15, 2023 at 03:36:02PM +0200, Marek Vasut wrote: > On 5/15/23 08:50, Traut Manuel LCPF-CH wrote: > > Hi Marek, > > Hi, > > > > 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 ? > > > > I tend to not change existing user-space interfaces. I would prefer to have an additional event or using sysfs. > > I am increasingly concerned about the race condition between change of > volume (via sysfs) and frequency (via SND_TONE) . So I would be banking > toward additional event, like SND_TONE_WITH_VOLUME or something along those > lines. This is just my $.02, but I don't see anything wrong with proposing an _additive_ change to the ABI such as this. My only concern is that this kind of change seems useful to any effect (e.g. SND_BEEP) and not limited to only tones. Unless volume adjustment is less useful for those? > > > > --- > > > NOTE: This uses approach similar to [1], except it is much simpler. > > > [1] https://patchwork.kernel.org/project/linux-input/cover/20230201152128.614439-1-manuel.traut@xxxxxx/ > > > > This one is more complex, because the mapping between duty cycle and volume is not linear. Probably it depends also on the used beeper hardware which values are doing a significant change in volume. Therefore the patchset introduced a mapping between volume levels and duty cycle times in the device-tree to allow user-space applications to control the beeper volume hardware independently. > > I wonder whether this mapping shouldn't be considered policy and left to > userspace to deal with, instead of swamping the kernel or DT with it ? I agree that the kernel need not try and linearize the values; in fact LEDs already have the same problem. I still feel however that imposing a unique maximum value (e.g. 50,000) is inappropriate because the range should remain the same regardless of the underlying HW implementation (PWM, class A/B, etc.). > > -- > Best regards, > Marek Vasut Kind regards, Jeff LaBundy
