bcm2835-analog-audio: Is my driver PWM, ALSA or neither

[Gottfried Haider]

Michael,

I don't have any suggestion to you actual question, but as someone who
builds (user-space) tools that interact with whatever peripheral I can
get my hands on: anything that would keep access to PWM open, and make
arbitration between it and audio more straightforward, would help
IMHO.

My most pressing issue with PWM today is that exporting a channel via
sysfs does not appear to cause events in udev. (At least this was the
case when I last checked on an 4.4-era kernel.) Because of this, there
is no sensible way of applying more relaxed access permissions to the
individual channel's sysfs nodes. And having to have root is
especially tricky to do with desktop applications...

I don't know much about the device model, but somehow exporting a gpio
pin via sysfs (drivers/gpio/gpiolib-sysfs.c) does create an "add"
event on udev, whereas the same on pwm (drivers/pwm/sysfs.c) doesn't
seem to cause one.

Just in case you stumble upon this area while you hack on the
alsa-cum-pwm driver :)

Best,

Gottfried