Re: PCI port I/O and memory-mapped I/O

On Tue, Sep 16, 2025 at 9:26 AM orbit <ordinarybit@proton.me> wrote:

> Hi,
>
> I am exploring PCI device driver at the moment were I could see my FreeBSD
> system having this Intel gigabit NIC detected as shown in the dmesg.
>
> em0: <Intel(R) PRO/1000 Legacy Network Connection 1.1.0> port
> 0xd010-0xd017 mem 0xf0000000-0xf001ffff irq 9 at device 3.0 on pci0
>
> Can someone confirm if the "port 0xd010-0xd017" and "mem
> 0xf0000000-0xf001ffff" pertains respectively to the PCI port I/O space
> and the PCI memory space being allocated to this Intel network driver upon
> attachment? If yes, does the Intel network controller chip use these ranges
> of memory addresses to map its control and status registers? If not, what
> are the usage of these port and memory address ranges?
>

Yes. Those are the addresses that the BIOS assigned to them, and that
FreeBSD picked up. That's the hardware register file for the network
controller.

The actual physical address is typically mapped 1:1 to the PCI Bus address,
but sometimes an iommu remaps.

Warmer