On many architectures, PCI devices are enumerated by the BIOS/firmware prior to the kernel booting. This is a problem if a PCI device is powered on after the PCI subsystem has scanned the various root complexes. Whereas PCI Hotplug devices have memory ranges reserved for them ahead of time, no such facility exists for bridges or other endpoints. The upcoming patches modifies PCI Hotplug to support static enumeration. Via the kcmdline, the user can specify how many bus numbers to reserve for hotplug bridges. This is necessary for the case where a bridge is hot-added after enumeration. The patches also allow the user to specify which bridges are hotpluggable, even though that bridge might not natively have that PCI capability. The kcmdline syntax for static enumeration is as follows: pci=hpbuses=<val>,enum=<device1>;<device2...> "hpbuses" is used to reserve bus numbers for hotplug bridges. "enum" is used mark bridges as hotpluggable. <device> has the form: <domain>:<bus>:<slot>.<func> All <device> values are in hexadecimal. These patches were tested on an x86_64 system that was booted over PXE and with a ramdisk. With static enumeration, the root filesystem cannot be on a PCI device. Reenumeration occurs during system initialization, prior to loading any devices. If an initrd normally mounts the real root filesystem from a PCI device, that device's addresses could change as a result of enumeration. The v0 patches and original discussions are at http://permalink.gmane.org/gmane.linux.kernel.pci/42082. Changes from v0 -> v1: * Rewrite, by adding support for hotpluggable bridges * New hpbuses kcmdline to reserve buses for hotplug bridges * Simplified enumeration code * Rebased to kernel 4.2-rc7 Jason Tang (7): PCI: Use child bus's number instead of assuming max+1 PCI: Track subordinate values in struct pci_bus PCI: Let kcmdline reserve bus numbers for hotplug bridges PCI: Add Kconfig option for static enumeration PCI: Let kcmdline specify static enumeration profile PCI: Use static enumeration to mark a bridge as hotpluggable PCI: Override firmware settings if static enumeration is set Documentation/kernel-parameters.txt | 11 ++++ drivers/pci/Kconfig | 12 ++++ drivers/pci/Makefile | 2 + drivers/pci/pci.c | 7 +++ drivers/pci/pci.h | 10 +++ drivers/pci/pci_static_enum.c | 120 ++++++++++++++++++++++++++++++++++++ drivers/pci/probe.c | 32 ++++++++-- include/linux/pci.h | 2 + 8 files changed, 191 insertions(+), 5 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
