On Tue, Sep 9, 2014 at 3:16 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Tuesday 09 September 2014 09:46:21 Liviu Dudau wrote: >> On Tue, Sep 09, 2014 at 06:54:21AM +0100, Yijing Wang wrote: >> > PCI domain(or named segment) is provided by firmware, in ACPI system, we evaluated it >> > by method "_SEG". in IA64 with ACPI, PCI hostbridge driver retrieves the domain from ACPI, >> > if it's absent, the default domain is zero. So I wonder why in DTS, if it's absent, we get >> > a auto increment domain value. >> >> Because you can have more than one hostbridge (rare, but not impossible) and unless you >> want to join the two segments, you might want to give it a different domain. > > I think you misunderstood the question. The difference is that in ACPI you > are required to specify the domain, while in DT it is optional with your > implementation. _SEG is actually optional, but the spec (ACPI r5.0, sec 6.5.6) says to assume domain 0 if _SEG is absent. Yijing mentioned ia64, which is relevant because PCI config accesses on ia64 are done via a firmware (SAL) interface, and the domain is part of that interface, so the kernel is actually required to supply the correct domain number (0 or _SEG value) for each host bridge. Bjorn -- 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
