On Tue, Dec 8, 2020 at 11:57 AM Thierry Reding <thierry.red...@gmail.com> wrote: > > Is this really that complicated? I sounds to me like the only thing that > you need is to have some sort of usage count for the prescaler. Whenever > you want to use the prescaler you check that usage count. If it is zero, > then you can just set it to whatever you need. If it isn't zero, that > means somebody else is already using it and you can't change it, which > means you have to check if you're trying to request the value that's > already set. If so, you can succeed, but otherwise you'll have to fail.
+1 I think your suggestion is an elegant solution to get the required behaviour. One possible complication is synchronization. The sysfs interface has a lock protecting against concurrent pwm_apply() calls. But the in-kernel API (e.g. pwm_apply_state()) doesn't seem to. This is not normally a problem when pwm bits are strictly separated. But in this case we have shared state (prescale value and use count), so we probably need to protect pwm_apply() with a mutex? Not sure if it is currently possible *in practice* for two regulator consumer drivers to call pwm_apply() from different threads. But Linux is slowly moving towards asynchronous probing. Uwe and Thierry, what is your opinion? Do you think we need to worry about synchronization?
