> Using `i2cdetect` on the i801 SMBus controller, I see that it reports no

You might try busses 0 and 1, too. Some laptops use the Synopsis
controller.

> Interestingly, I see warnings in dmesg upon running the above i2cdetect
> command.

How many? If it is in the 120 range, then every access from i2cdetect
fails with it.