Hello,
(I haven't a deep knowledge of the PCIe specification, maybe I'm just
missing something)
is there a way to force the PCI subsystem to assign a bus-number to
every PCIe bridge, even if there is nothing connected?
My aim is to have a bus enumeration constant and independent from what
I plugged on the system. So, I can associate a physical slot to linux
device address bb:dd.f. Is it possible?
I can do the mapping with a simple shell script by discovering the
"new" bus number, but I'm wondering if there is a way to have a
constant bus enumeration.
My Humble Observation
---------------------
It seems (to me) that for PCI the kernel assigns a bus-number to every
PCI bridges and sub-bridges even if there is nothing connected:
e.g. from lspci -t
[...]
+-1e.0-[04-05]----0c.0-[05]--
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 92)
04:0c.0 PCI bridge: Texas Instruments PCI2050 PCI-to-PCI Bridge (rev
02)
The behavior on PCIe seems different. When there is nothing plugged on
a bus, then the kernel doesn't assign any bus-number and it doesn't
detect any PCI-Bridge at all. So, when I reboot the system with a new
PCIe card the bus enumeration may change.
I tried to use the following pci kernel parameters:
assign-busses : because I want to force the kernel to re-enumerate the
busses, hopefully _all_ buses even if they are empty.
pcie_scan_all : not clear the explanation, but it sounds like it tells
to the kernel to inspect everything.
bfsort : because, maybe, for a bfsort it must assign a number to each
bridge at the same level before inspect the next one.
noacpi : in order to scan independently from BIOS information
The result is always the same (empty buses are not enumerated).
Thank you :)
--
Federico Vaga
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