What is the minimum high drive gpio source current when VDD=2.1V?

[nikolrobottesla]

The gpio specifications table lists 3mA for VDD greater than 1.7V and 6mA for voltages greater than 2.7V but what about in between?

Would a linear approximation between those numbers be accurate to within 0.5mA?

[Ole Bauck]

It is not linear, but you could approximate it to that. I don't know if it is within 0.5mA though.

3mA when VDD is greater than 1.7V is with a pad voltage of 0.4V, if you increase the current the pad voltage will increase. We recommend that you sink current instead of sourcing current from the chip, and recommended total current should be less than about 15mA.

See this and this thread.