[londons_explore]

> reading brightness, contrast or volume from the monitor fails about 30% of the time

There is a good chance this is because the read is done too fast. If it gets less reliable with a super long HDMI cable then it's almost certainly the clock speed.

I2C is a clocked protocol where the host (the laptop) decides the clock speed. It isn't designed as a high speed data transfer mechanism, and requires that all the signals get to the other end of the wire and back all within every clock cycle. Since there is very little data to send, a clock speed of 10kHz should do the job just fine. But I bet the hardware is set to something silly like 10 MHz by default, since it probably uses the same I2C drivers and hardware blocks as used for communicating with other things on-chip and within the system.