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

Ozgur Karatas ozgurk at
Tue Apr 12 15:10:45 EDT 2022

On Tue, Apr 12, 2022 at 11:00 PM Khalid F. Sabzwari <kfsabzwari at>

> Hi,


> My CPU is Intel x86 (Broadwell DE). I want to write to the command
> register of the management ethernet PHY's PCIe
> config 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 dont think this right way, there should be a phy.h header file in kernel
and i think should use PHY Abstraction Layer.

> I have bus/device/function info for this management PHY which is already
> set by the BIOS.
> thanks,
> Khalid.
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