Although my use case is specific to Raspberry Pi, I think the question is a general USB Host port question.
When a phone/tablet (especially iphone and ipad) is connected to a Raspberry Pi 2, if its battery getting low, it will successfully charge from the RPi2 USB port.
The problem is, even with a 2A power supply to the RPi2, when a larger phone or tablet is charging that can wreak havoc on other USB devices or the RPi2 itself. (I discovered this by having an application start crashing but only when the RPi2 was connected to an iPhone 6S plus with a battery at 50% or less.)
I know some hubs, such as bus-powered hubs, somehow inform a connected phone "don't even try to charge yourself", so I assume there is a way to have a Raspberry Pi's USB ports do the same, eg, inform connected devices that the maximum current available is 100ma.
How can a RPi2 (or its USB port) be modified so it informs attached USB devices not to try charging from the port.
Note: I do need an active data connection, I just need to prevent the attached phone or tablet to not draw too much current for the RPi2 to handle.