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"In some cases, especially on modern laptops with a lot of PCI and cardbus bridges, we're unable to assign correct secondary/subordinate bus numbers to all cardbus bridges due to BIOS limitations unless we are using "pci=assign-busses" boot option." -- Ivan Kokshaysky (from a patch comment) Without it, Cardbus cards inserted are never seen by PCI because the parent PCI-PCI Bridge of the Cardbus bridge will not pass and translate Type 1 PCI configuration cycles correctly and the system will fail to find and initialise the PCI devices in the system. Reference: PCI-PCI Bridges: PCI Configuration Cycles and PCI Bus Numbering: http://www.science.unitn.it/~fiorella/guidelinux/tlk/node72.html The reason for this is that: ``All PCI busses located behind a PCI-PCI bridge must reside between the secondary bus number and the subordinate bus number (inclusive).'' "pci=assign-busses" makes pcibios_assign_all_busses return 1 and this turns on PCI renumbering during PCI probing. Alan suggested to use DMI automatically set assign-busses on problem systems. The only question for me was where to put it. I put it directly before scanning PCI bus into pcibios_scan_root() because it's called from legacy, acpi and numa and so it can be one place for all systems and configurations which may need it. AMD64 Laptops are also affected and fixed by assign-busses, and the code is also incuded from arch/x86_64/pci/ that place will also work for x86_64 kernels, I only ifdef'-ed the x86-only Laptop in this example. Affected and known or assumed to be fixed with it are (found by googling): * ASUS Z71V and L3s * Samsung X20 * Compaq R3140us and all Compaq R3000 series laptops with TI1620 Controller, also Compaq R4000 series (from a kernel.org bugreport) * HP zv5000z (AMD64 3700+, known that fixup_parent_subordinate_busnr fixes it) * HP zv5200z * IBM ThinkPad 240 * An IBM ThinkPad (1.8 GHz Pentium M) debugged by Pavel Machek gives the correspondig message which detects the possible problem. * MSI S260 / Medion SIM 2100 MD 95600 The patch also expands the "try pci=assign-busses" warning so testers will help us to update the DMI table. Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Dominik Brodowski <linux@dominikbrodowski.net> Cc: Russell King <rmk@arm.linux.org.uk> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
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