RE: bnx2x in 4.6rc7 with FW 7.13.1.0 not present

Upgrading a system from kernel 4.2 to 4.6rc7, there is an extra 2 minute delay
while booting due to these problems:

    [   47.977221] bnx2x 0000:04:00.1: Direct firmware load for bnx2x/bnx2x-e2-
7.13.1.0.fw failed with error -2

... 

Could the driver fall back to an older firmware version more gracefully?

No.

The internal FW isn't necessarily backward compatible [there are some
Compatibility in fastpath in order to support VFs, but not in general].
Doing what you ask would means filling the driver with a lot of legacy code
for older FWs, adding per-FW version HSI files, etc.

So in short - if you've installed a fresh kernel on top of an existing distro
that lacked the latest firmware in its filesystem, getting that missing 
.bin file from linux-firmware is the way to go.

Cheers,
Yuval