How to write to a PCIe config space during kernel boot up

Khalid F. Sabzwari kfsabzwari at
Tue Apr 12 14:59:31 EDT 2022

Hi,My CPU is Intel x86 (Broadwell DE). I want to write to the command register of the management ethernet PHY's PCIeconfig space during Linux boot up. And I want to do that before kernel start loading the igb (ethernet) driver for this PHY.Can I do that inside the start_kernel() routine in init.main.c, or is the driver is already installed once code reaches this point (I am assuming probably not) ?If this is the correct routine to do this job, is there any kernel code that I can use to write to this config space? I have bus/device/function info for this management PHY which is already set by the BIOS.
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