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I am on a custom board using an i.MX6. I am using Yocto (Pyro) to build my kernel (4.14.16).
I am using the generic imx6qdl.dtsi device tree entry for PWM2 to drive the fan and it appears to work fine. The fan has a Tachometer input, which is connected to GPIO2_7. How do I read the fan speed? I have seen device tree blobs for cooling devices, but none of the examples seem to have a tachometer to monitor the fan's speed.
I was unable to find a device tree solution, but found enough code snippets to make an application to read it. Basically I just set up an interrupt on the GPIO and used clock_gettime to measure the period between edges. It requires a lot of filtering, but I am only using it to make sure the fan is running so that is fine.
/sys/class/hwmon/(and/sys/class/pwm/)? I'm guessing yes, but just want to be sure there isn't an easy solution there. – derobert Mar 8 at 20:53/sys/class/pwm/but there was no mechanism to read back the speed (just the PWM that i had set it to). All that I have in/sys/class/hwmonwere temperature sensors. – Eskimoalva Mar 11 at 12:23