In tg3_chip_reset(), the PCI_EXPRESS change is taken from the Linux
tg3 driver. I am not sure what exactly it does (it is not documented
in the Linux driver), but it is necessary for the NIC to work
correctly.

From: Daniel Mealha Cabrita <dancab@utfpr.edu.br>

I've added tg3-5721 support for gPXE, the patch (against gpxe-0.9.3) is
attached to this message.

This chipset is present in HP ML150 G2 servers (possibly other HP machines
as well).