PCI: optionally sort device lists breadth-first

Problem:
New Dell PowerEdge servers have 2 embedded ethernet ports, which are
labeled NIC1 and NIC2 on the chassis, in the BIOS setup screens, and
in the printed documentation.  Assuming no other add-in ethernet ports
in the system, Linux 2.4 kernels name these eth0 and eth1
respectively.  Many people have come to expect this naming.  Linux 2.6
kernels name these eth1 and eth0 respectively (backwards from
expectations).  I also have reports that various Sun and HP servers
have similar behavior.


Root cause:
Linux 2.4 kernels walk the pci_devices list, which happens to be
sorted in breadth-first order (or pcbios_find_device order on i386,
which most often is breadth-first also).  2.6 kernels have both the
pci_devices list and the pci_bus_type.klist_devices list, the latter
is what is walked at driver load time to match the pci_id tables; this
klist happens to be in depth-first order.

On systems where, for physical routing reasons, NIC1 appears on a
lower bus number than NIC2, but NIC2's bridge is discovered first in
the depth-first ordering, NIC2 will be discovered before NIC1.  If the
list were sorted breadth-first, NIC1 would be discovered before NIC2.

A PowerEdge 1955 system has the following topology which easily
exhibits the difference between depth-first and breadth-first device
lists.

-[0000:00]-+-00.0  Intel Corporation 5000P Chipset Memory Controller Hub
           +-02.0-[0000:03-08]--+-00.0-[0000:04-07]--+-00.0-[0000:05-06]----00.0-[0000:06]----00.0  Broadcom Corporation NetXtreme II BCM5708S Gigabit Ethernet (labeled NIC2, 2.4 kernel name eth1, 2.6 kernel name eth0)
           +-1c.0-[0000:01-02]----00.0-[0000:02]----00.0  Broadcom Corporation NetXtreme II BCM5708S Gigabit Ethernet (labeled NIC1, 2.4 kernel name eth0, 2.6 kernel name eth1)


Other factors, such as device driver load order and the presence of
PCI slots at various points in the bus hierarchy further complicate
this problem; I'm not trying to solve those here, just restore the
device order, and thus basic behavior, that 2.4 kernels had.


Solution:

The solution can come in multiple steps.

Suggested fix #1: kernel
Patch below optionally sorts the two device lists into breadth-first
ordering to maintain compatibility with 2.4 kernels.  It adds two new
command line options:
  pci=bfsort
  pci=nobfsort
to force the sort order, or not, as you wish.  It also adds DMI checks
for the specific Dell systems which exhibit "backwards" ordering, to
make them "right".


Suggested fix #2: udev rules from userland
Many people also have the expectation that embedded NICs are always
discovered before add-in NICs (which this patch does not try to do).
Using the PCI IRQ Routing Table provided by system BIOS, it's easy to
determine which PCI devices are embedded, or if add-in, which PCI slot
they're in.  I'm working on a tool that would allow udev to name
ethernet devices in ascending embedded, slot 1 .. slot N order,
subsort by PCI bus/dev/fn breadth-first.  It'll be possible to use it
independent of udev as well for those distributions that don't use
udev in their installers.

Suggested fix #3: system board routing rules
One can constrain the system board layout to put NIC1 ahead of NIC2
regardless of breadth-first or depth-first discovery order.  This adds
a significant level of complexity to board routing, and may not be
possible in all instances (witness the above systems from several
major manufacturers).  I don't want to encourage this particular train
of thought too far, at the expense of not doing #1 or #2 above.


Feedback appreciated.  Patch tested on a Dell PowerEdge 1955 blade
with 2.6.18.

You'll also note I took some liberty and temporarily break the klist
abstraction to simplify and speed up the sort algorithm.  I think
that's both safe and appropriate in this instance.


Signed-off-by: Matt Domsch <Matt_Domsch@dell.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index ff571f9..dd00fd5 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1231,6 +1231,11 @@ and is between 256 and 4096 characters. It is defined in the file
 				machine check when some devices' config space
 				is read. But various workarounds are disabled
 				and some IOMMU drivers will not work.
+		bfsort		Sort PCI devices into breadth-first order.
+				This sorting is done to get a device
+				order compatible with older (<= 2.4) kernels.
+		nobfsort	Don't sort PCI devices into breadth-first order.
+
 	pcmv=		[HW,PCMCIA] BadgePAD 4
 
 	pd.		[PARIDE]