On Tue, Feb 12, 2013 at 11:05:28PM +0000, Arnd Bergmann wrote: > On Tuesday 12 February 2013, Jason Gunthorpe wrote: > > PCI-E hotplug can be supported through the generic /sys/bus/pci/rescan > > mechanism, which forces a rediscovery/re-evaluation of all the buses > > in the system. The PCI core is smart enough to know what it can/can > > not reassign and can move the bridge windows around (IIRC most of the > > issues here are resolved these days?). > > > > For PCI-E, the root port bridge can be placed anywhere in the host > > aperture, so as long as the host aperture isn't filled the core can > > allocate a memory region for the now active port. > > > > Thomas's driver should support this as the regions and windows are all > > properly dynamic. > > Ah, so you only allow hotplugging into the root ports, but not behind > additional bridges that have active devices on them, right? > I guess that is a common limitation for PCIe hotplugging. In all the cases I've worked with, it has been a root port hot plug, but I could imagine something like ExpressCard requiring a second bridge. The standard answer is to leave appropriate gaps. My *guess* on this matter is that on x86 the gaps are left, as appropriate, by the boot firmware. Eg an ExpressCard slot will always have a window assigned to its bridge and Linux would typically not reassign it (or similar). PCI core support for firmware-less embedded will someday need to do something similar, eg via a special DT attribute on hot plug capable ports. Just to circle back on this whole thread - Thomas's solution is pretty good, it covers pretty much all the use cases. I think it is a good place to start, and as the firmware-less 'drivers/pci/host' concept develops the right support will eventually come, as everyone is now aware of the need to control the host bridge aperture from the core PCI code. Jason -- 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
