qemu returns a black screen emulating on a raspberry pi 2 (rasbian)

[Songhua Liu]

I used the kernel in your repo kernel-qemu . nothing returned but a black window by qemu.

here's the log

WARNING: Image format was not specified for '/path/to/pi2-16gb.img' and probing guessed raw.
        Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
        Specify the 'raw' format explicitly to remove the restrictions.

It even didn't try to uncompress the kernel...

Here's the full issue for this scenario.

Thank you a million if you can help!