Hi Henrique, On Mon, 26 Feb 2007 15:06:35 -0300, Henrique de Moraes Holschuh wrote: > On Mon, 26 Feb 2007, Jean Delvare wrote: > > Either way, I do not think that knowing the last measured speed is that > > useful. Given that it may be completely unrelated with the current > > It is, actually, because it lets one mess with the embedded controller and > completely override the fan control loop while not letting anyone else > notice (i.e. without disturbing fan monitor applets, etc). > > Check http://thinkwiki.org/wiki/Embedded_Controller_Firmware and > http://thinkwiki.org/wiki/ACPI_fan_control_script if you are > curious about the whys for these weird things. I don't really have time for such long reads, sorry. If there's anything in particular you think I should know, just tell me. > > value, I'd rather return -ENXIO or -ERETRY if there is a reasonable > > chance to get a valid reading soon after. If applications wants to > > I will return the stale value or an error, then. Not returning the stale > value actually requires that I implement some sort of back/white lists to > differentiate models which don't have the stale tachometer bug from those > that do... or I need to detect that the tachometer seems to be stuck. I see. In that case I am fine with you returning the stale value. After all, the driver is supposed to return the value as read from the hardware. > > pwm#_enable = 0 means fan# at full speed, _not_ fan# stopped. Fan# stopped > > is pwm#_enable = 1 and pwm# = 0. > > The hwmon sysfs interface documentation is not clear on that. Turning PWM > off might lock the hardware into 0% duty or 100% duty depending on how it > was designed. Feel free to submit a patch improving the documentation. > Anyway, I can map it to: > pwm_enable = 0: disengaged mode on > 1: manual mode on > 2+: EC auto mode on (default) > > no problem. > (...) > Ok. pwm = 0 in manual mode will stop fan, 1..255 will be mapped to 1..7 to > select the thinkpad fan level, which the EC itself will map to (usually) > three different speeds. Yes, this looks good. > BTW, ibm-acpi implements a "fan watchdog", to help fan-control userspace > applications. It resets the fan to a safe "on" mode if nothing tries any > control operation on the fans in a given time period. > > Is there any interest in trying for a fan-watchdog generic interface, or > should I just implement that in sysfs as I see fit for ibm-acpi? We don't have anything like that in the other drivers. I guess it only applies to manual mode? The idea is interesting, I have to admit. I don't have a particular opinion on how to implement that (specific vs standard), do as you wish. -- Jean Delvare
