How to read extended PCIE configuration space in Linux?

I've tried both reading userspace pci entry under /proc/bus/pci directory and calling kernel space API pci_read_config_word() in the driver. but it seems both can only read pci basic configuration space, offset less than 0x100.

The offset I want to read is beyond 0x100, could anyon开发者_运维百科e tell me how to do it in Linux? if done in kernel space, telling which API to call would be very appreciated. Thank you very much!

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pci_read_config_word() is the correct API, but to access extended configuration space you need to use MMCONFIG. This is not something you set up; the kernel should choose to use MMCONFIG by itself if available. Do you see anything like

e0000000-efffffff : PCI MMCONFIG 0000 [bus 00-ff]

in /proc/iomem? Also in your kernel log, you should see some lines about the ACPI MCFG table and MMCONFIG:

ACPI: MCFG 00000000bb7fec63 0003C (v01 LENOVO TP-6U    00001410 LNVO 00000001)
...
PCI: MMCONFIG for domain 0000 [bus 00-ff] at [mem 0xe0000000-0xefffffff] (base 0xe0000000)

and of course your kernel needs to be built with CONFIG_PCI_MMCONFIG=y.

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I believe that the extended configuration space is restricted for non-root users, at least that's the behaviour I face when executing lspci when not root. You can use sudo lspci -Qkxxxxnnv to view all 0xff0 (4080) configuration space data, and some other useful stuff.

$ sudo lspci -Qkxxxxnnv

00:1d.0 PCI bridge [0604]: Intel Corporation Comet Lake PCI Express ...
Flags: bus master, fast devsel, latency 0, IRQ 124
...
Kernel driver in use: pcieport
00: 86 80 98 a3 07 04 10 00 f0 00 04 06 10 00 81 00
...
ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

See: PCI Configuration Space