Power Brick control #64

Hi,

The FW USB-C PD is a "dual" mode device, in that it can both source and sink power.
This works quite well when one plugs in a "source" mode device or a "sink" mode device.
There is no ambiguity there.
The problem comes when one has a Power Brick that is also a "dual" mode device.

dual mode device <=> dual mode device
Who wins, who charges who?

I would like to add an ectool command so that a user can hint to a particular USB port whether it should act as a source or a sink when it sees a dual mode device.
It allows the user to override unexpected behavior.

I am happy to edit the EC source code myself to implement this feature.
My question is, what command does the EC need to send the USB-C port to change it from being a "dual" mode device to be a "sink" mode only device?