I am working on a conversion of ibm-acpi to sysfs, and in the process I am trying to do away with every non-generic interface I can. At least two ibm-acpi interfaces map directly to hwmon/lm-sensors style: fan and thermal. I'd like to expose them as hwmon attributes, using the hwmon generic interfaces for fan control and thermal sensor readings. I would really appreciate feedback from the lm-sensors/hwmon group on how to best achieve that. Thermal is relatively easy. A thinkpad has either 8 or up to 16 thermal sensors (typically, 12 sensors), and I can simply export them as temp##_input, already converted to milidegree Celcius. However, some thinkpad thermal sensors are hotswappable (they're inside battery packs, for example). What is the recommended way to deal with that? I was planning to return -ENXIO for sensors thare are currently unavailable, and I could also try to make their sysfs attributes go away (and come back again) when the driver detects such a change -- note that I don't get events from the thinkpad firmware when a sensor gets disconnected or reconnected, I need to poll them to know that). Is that the recommended way to go about it? Or should I just leave all entries there and return -ENXIO on the invalid ones (the firmware returns -128 for invalid sensors). fan control is a bit more hard to map to the hwmon interface, as the thinkpad firmware exports a higher level interface than your regular thermal-and-fan-monitor chip (and it is far less documented and far more buggy than regular chips :p): Most thinkpads have a tachometer that returns data in RPM, and that gets mapped to fan##_input. The tachometer can get stale in fan control disengaged mode (see below), how should I export that information to userspace? There is nothing in the standard hwmon sysfs for that, and it *is* useful to userspace to know the last measured speed, so I don't want to return -ENXIO or somesuch on fan##_input... What do you guys suggest I do? Add an ibm-acpi specific fan##_input_valid attribute that reads 0/1? Or not export that information in the first place? Should I propose such an attribute to the generic interface? The thinkpad EC has three modes of fan operation: manual, where there are seven fan speed levels (0=off, 1=slowest, 7=fastest) that map to different speeds (usually fan stopped plus three different speeds, so it is not a 1:1 mapping). auto, where it selects one of the levels by itself, and disengaged, where it kicks the fan to its highest speed (which usually is quite higher than level 7). The levels are closed-loop-controlled, and track a model-specific desired RPM value. That allows for consistent hardware behaviour with fans that are going old or are somewhat dirty. I was thinking of using pwm##_enable to: force manual mode, level 0 (fan off) when pwm##_enable is 0, force manual mode when it is 1, and force auto mode when it is 2+. I can query what mode the firmware is in, so reading pwm##_enable is not a problem. The level for manual mode would be set by pwm##: if it is 0, force level 0. If it is between 1..90, I'd select one of the six non-stopped fan speed levels. If it is above 90, I'd select disengaged mode. Reading pwm## is not easy. It is indeterminate if pwm##_enable is set to 2+ (auto mode)... what should I return, then? For manual mode, I was planning to return the quantized value (i.e. if 1..26 select fan level 1, a read will return 26). For disengaged value (a write of 90..100 with pwm##_enable set to 1), I'd always return 100. Is that a good way to implement it? Note that this interface does not map exacly what the hardware is doing. When one sets the fan to disengaged mode, the firmware slowly increases fan speed until it hits max, for example. There is no way to get any feedback on what the firmware is *really* doing to the fan, other than the tachometer readings. I was going to place all fan attributes in a sysfs group (subdirectory) named "fan", and all thermal attributes in a sysfs group named "thermal". Is that acceptable? -- "One disk to rule them all, One disk to find them. One disk to bring them all and in the darkness grind them. In the Land of Redmond where the shadows lie." -- The Silicon Valley Tarot Henrique Holschuh
