1*4882a593SmuzhiyunKernel driver power_meter 2*4882a593Smuzhiyun========================= 3*4882a593Smuzhiyun 4*4882a593SmuzhiyunThis driver talks to ACPI 4.0 power meters. 5*4882a593Smuzhiyun 6*4882a593SmuzhiyunSupported systems: 7*4882a593Smuzhiyun 8*4882a593Smuzhiyun * Any recent system with ACPI 4.0. 9*4882a593Smuzhiyun 10*4882a593Smuzhiyun Prefix: 'power_meter' 11*4882a593Smuzhiyun 12*4882a593Smuzhiyun Datasheet: https://uefi.org/specifications, section 10.4. 13*4882a593Smuzhiyun 14*4882a593SmuzhiyunAuthor: Darrick J. Wong 15*4882a593Smuzhiyun 16*4882a593SmuzhiyunDescription 17*4882a593Smuzhiyun----------- 18*4882a593Smuzhiyun 19*4882a593SmuzhiyunThis driver implements sensor reading support for the power meters exposed in 20*4882a593Smuzhiyunthe ACPI 4.0 spec (Chapter 10.4). These devices have a simple set of 21*4882a593Smuzhiyunfeatures--a power meter that returns average power use over a configurable 22*4882a593Smuzhiyuninterval, an optional capping mechanism, and a couple of trip points. The 23*4882a593Smuzhiyunsysfs interface conforms with the specification outlined in the "Power" section 24*4882a593Smuzhiyunof Documentation/hwmon/sysfs-interface.rst. 25*4882a593Smuzhiyun 26*4882a593SmuzhiyunSpecial Features 27*4882a593Smuzhiyun---------------- 28*4882a593Smuzhiyun 29*4882a593SmuzhiyunThe `power[1-*]_is_battery` knob indicates if the power supply is a battery. 30*4882a593SmuzhiyunBoth `power[1-*]_average_{min,max}` must be set before the trip points will work. 31*4882a593SmuzhiyunWhen both of them are set, an ACPI event will be broadcast on the ACPI netlink 32*4882a593Smuzhiyunsocket and a poll notification will be sent to the appropriate 33*4882a593Smuzhiyun`power[1-*]_average` sysfs file. 34*4882a593Smuzhiyun 35*4882a593SmuzhiyunThe `power[1-*]_{model_number, serial_number, oem_info}` fields display 36*4882a593Smuzhiyunarbitrary strings that ACPI provides with the meter. The measures/ directory 37*4882a593Smuzhiyuncontains symlinks to the devices that this meter measures. 38*4882a593Smuzhiyun 39*4882a593SmuzhiyunSome computers have the ability to enforce a power cap in hardware. If this is 40*4882a593Smuzhiyunthe case, the `power[1-*]_cap` and related sysfs files will appear. When the 41*4882a593Smuzhiyunaverage power consumption exceeds the cap, an ACPI event will be broadcast on 42*4882a593Smuzhiyunthe netlink event socket and a poll notification will be sent to the 43*4882a593Smuzhiyunappropriate `power[1-*]_alarm` file to indicate that capping has begun, and the 44*4882a593Smuzhiyunhardware has taken action to reduce power consumption. Most likely this will 45*4882a593Smuzhiyunresult in reduced performance. 46*4882a593Smuzhiyun 47*4882a593SmuzhiyunThere are a few other ACPI notifications that can be sent by the firmware. In 48*4882a593Smuzhiyunall cases the ACPI event will be broadcast on the ACPI netlink event socket as 49*4882a593Smuzhiyunwell as sent as a poll notification to a sysfs file. The events are as 50*4882a593Smuzhiyunfollows: 51*4882a593Smuzhiyun 52*4882a593Smuzhiyun`power[1-*]_cap` will be notified if the firmware changes the power cap. 53*4882a593Smuzhiyun`power[1-*]_interval` will be notified if the firmware changes the averaging 54*4882a593Smuzhiyuninterval. 55