How to capture hdmi AV signal through the micro USB port

Let's say I connect my smartphone's micro USB port to a micro HDMI port of a video handycam, with a MHL cable.
I want to capture the full HD hdmi signal from the camera and display it on the phone screen.

We suppose the phone doesn't have a dedicated MHL chip (even if it had one, it would be for output from the phone not for input);
so I won't be using the MHL standard functionality.
BUT, when we connect the camera's HDMI port with the smartphone's USB port, we will still have the signal containing hdmi audio/video information from the camera, at the smartphone usb port. (we cannot say that there is no signal there, right?)

So that's exactly the issue here- to catch this signal from the USB port without a MHL IC in the phone or converter, and process it with the software (the driver), knowing that it contains hdmi AV information.
I need to know how I can capture the audio/video signal output by the camera, with the phone through its micro USB port (I want to write the driver for that).

Maybe knowing how the pin mapping between the two ports is done by the mhl cable (namely what usb pin is connected to what hdmi pin) would be helpful to know, too, but I couldn't find on the net.

Any hint is appreciated.
Thanks.