On May 11, Brian Masney wrote: > On Thu, May 11, 2017 at 09:35:12AM +0000, Lorenzo BIANCONI wrote: > > > If desired, one way to get rid of the enabled flag would be to > > > add support for runtime power management to automatically shutdown > > > the chip after a period of inactivity. See > > > https://lkml.org/lkml/2017/4/25/101 for an example. > > > > > > > I am not a pm_runtime expert but according to the documentation runtime_suspend > > callback is called when device's usage counter and counter of 'active' children > > of the device are equal to 0. Moreover device possible states are 'disabled' > > (HTS221_REG_CNTRL1_ADDR register set to 0) or 'active' (HTS221_REG_CNTRL1_ADDR > > register configured with a given sample rate). In the first condition > > runtime_suspend() will not take any effect whereas in the latter one the > > callback will not be called since device's usage counter is grater than 0. > > Moreover implement system-wide pm support through runtime pm support just to > > avoid a boolean flag seems a little bit overkill to me. What do you think? > > Is my understanding correct? Hi Brian, > > Sorry, I should have also said that I didn't think that runtime PM was > absolutely required. I also agree adding runtime PM just to remove the > flag is overkill. Runtime PM is nice to have if this sensor is hooked > up to something that may run off a battery (such as a weather station) > to help conserve power. The flag removal is a by product of this. :) > > As for the runtime PM reference count, when your driver is initialized, > keep the device off so that the device usage count is initially zero. > Wrap your _write_raw() and _read_raw() functions with the runtime PM > calls and the device will power on and off as needed. I mean ->runtime_suspend()/->runtime_resume() are never called by the PM core when the sensor is active since usage count is always grater than 0. On the contrary when usage count is equal to 0 the sensor is already disabled, so the ODR configuration does not make any difference. Regards, Lorenzo > > Brian -- -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
