Hi Guenter, On Tue, Nov 13, 2018 at 09:21:02AM -0800, Guenter Roeck wrote: > > > > INA3221 supports both continuous and single-shot modes. When > > > > running in the continuous mode, it keeps measuring the inputs > > > > and converting them to the data register even if there are no > > > > users reading the data out. In this use case, this could be a > > > > power waste. > > > > > > > > So this patch adds a single-shot mode support so that ina3221 > > > > could do measurement and conversion only if users trigger it, > > > > depending on the use case where it only needs to poll data in > > > > a lower frequency. > > > > > > > > The change also exposes "mode" and "available_modes" nodes to > > > > allow users to switch between two operating modes. > > > > > > > Lots and lots of complexity for little gain. Sorry, I don't see > > > the point of this change. > > > > The chip is causing considerable power waste on battery-powered > > devices so we typically use it running in the single-shot mode. > > And you need to be able to do that with a sysfs attribute ? > Are you planning to have some code switching back and forth > between the modes ? > > You'll need to provide a good rationale why this needs to be > runtime configurable. Honestly, our old downstream driver didn't expose it via sysfs. Instead, it had a built-in "governor" to switch modes based on the CPU hotplug state and cpufreq. However, the interface used to register a CPU hotplug notification was already deprecated. And I don't feel this governor is generic enough to be present in the mainline code. For me, it's not that necessary to be a sysfs attribute. I try to add it merely because I cannot find a good criteria for the mode switching in a hwmon driver. So having an open sysfs node may allow user space power daemon to decide its operating mode, since it knows which power mode the system is running at: full speed (charging/charged) or power saving (on-battery), and it knows how often this exact service will poll the sensor data. An alternative way (without the sysfs node), after looking at other hwmon code, could be to have a timed polling thread and read data using an update_interval value from ABI. This might turn out to be more complicated as it'll also involve settings of hardware averaging and conversion time. Above all, I cannot figure out a good threshold of update_interval to switch modes. If you can give some advice of a better implementation, that'd be great. Thanks Nicolin
