I'm using Raspberry PI OS image is 2021-03-04-raspios-buster-armhf-lite and I spotted in the product sheet for the Raspberry PI CM4IO (Compute Module 4 IO board) that it was i2c-10 assigned for the fan.
Certainly seems to be active..
sudo i2cdetect -l
i2c-10 i2c i2c-11-mux (chan_id 1) I2C adapter
i2c-1 i2c bcm2835 (i2c@7e804000) I2C adapter
i2c-11 i2c bcm2835 (i2c@7e205000) I2C adapter
i2c-0 i2c i2c-11-mux (chan_id 0) I2C adapter
i2cdetect -y 10
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- 0c -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 2f
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- 51 -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
I have failed to find any more information via internet searches for this i2c resource... Though the RPI docs seem to point to it being a EMC2301 chipset. https://ww1.microchip.com/downloads/en/DeviceDoc/2301.pdf
Does anyone have any pointers or examples of using the i2c Fan controller on a CM4IO?
Thanks in advance