structure of /sys/class/pci_bus

[Jon Smirl <jonsmirl@gmail.com>]

I'm having some trouble with the way sysfs is structured for multiple
PCI busses.

[jonsmirl@smirl /]$ ls sys/class/pci_bus
0000:00  0000:01  0000:02

I have three busses in my system. It is Intel i875P.

[jonsmirl@smirl /]$ ls sys/class/pci_bus/0000:00
bridge  cpuaffinity

Normal pci_bus entry

[jonsmirl@smirl /]$ ls sys/class/pci_bus/0000:00/bridge -l
lrwxrwxrwx  1 root root 0 Sep  4 13:10
sys/class/pci_bus/0000:00/bridge -> ../../../devices/pci0000:00

bridge for bus 0 is pci0000:00

[jonsmirl@smirl /]$ ls sys/class/pci_bus/0000:01/bridge -l
lrwxrwxrwx  1 root root 0 Sep  4 13:10
sys/class/pci_bus/0000:01/bridge ->
../../../devices/pci0000:00/0000:00:01.0

bridge for bus 0 is pci0000:00/0000:00:01.0

[jonsmirl@smirl /]$ ls sys/class/pci_bus/0000:02/bridge -l
lrwxrwxrwx  1 root root 0 Sep  4 13:10
sys/class/pci_bus/0000:02/bridge ->
../../../devices/pci0000:00/0000:00:1e.0

bridge for bus 2 is pci0000:00/0000:00:1e.0

[jonsmirl@smirl /]$ ls sys/class/pci_bus/0000:00/bridge
0000:00:00.0  0000:00:1d.0  0000:00:1d.2  0000:00:1d.7  0000:00:1f.0 
0000:00:1f.2  0000:00:1f.5  power
0000:00:01.0  0000:00:1d.1  0000:00:1d.3  0000:00:1e.0  0000:00:1f.1 
0000:00:1f.3  detach_state

But bridge 0 is not linked to a bridge node. It is linked to the host
device node instead. This is not symetrical with bus 1 and 2.

[jonsmirl@smirl /]$ ls sys/class/pci_bus/0000:01/bridge
0000:01:00.0  class   detach_state  irq    resource          subsystem_vendor 
0000:01:00.1  config  device        power  subsystem_device  vendor

This is what a normal bridge node looks like

[jonsmirl@smirl /]$ cat sys/class/pci_bus/0000:01/bridge/class
0x060400

Bridge is a PCI bridge

[jonsmirl@smirl /]$ ls sys/class/pci_bus/0000:00/bridge/0000:00:00.0
class  config  detach_state  device  irq  power  resource 
subsystem_device  subsystem_vendor  vendor

This is the real bridge node for bus 0.

[jonsmirl@smirl /]$ cat sys/class/pci_bus/0000:00/bridge/0000:00:00.0/class
0x060000

Class is Host bridge.  Host bridge has two nodes in sysfs, a device
node, pci0000:00, and a pci_device node, 0000:00:00.0.

[jonsmirl@smirl /]$ ls sys/devices
pci0000:00  platform  system

This shows the top level Host bridge.

Starting from here, how I am supposed to figure out that 0000:00:00.0
is the PCI device for controlling this bridge?

-- 
Jon Smirl
jonsmirl@gmail.com