On Mon, Feb 01, 2016 at 03:25:07PM +0000, Lorenzo Pieralisi wrote: > On Sat, Jan 30, 2016 at 07:30:27AM -0600, Bjorn Helgaas wrote: > > [...] > > > > Most non-UEFI firmwares I have seen on ARM rely on device specific > > > driver like synopsys etc. to do the device initialization and ask > > > kernel to do the enumeration. > > > > > > ACPI systems on the other hand handle the resource assignment before > > > the OS starts. > > > > My guess is that this is more of a tradition than anything actually > > required by the spec. > > I share your opinion, and that tradition on ARM64 should be built > on top of existing DT based systems where the bootloader assigns > *NOTHING* in 90% of designs. > > That's why I want to see resource claiming carried out by default > on ACPI on ARM64, this would foster the tradition :), hopefully. > > > The bottom line is that Linux can't rely on much consistency across > > the universe of architectures and firmwares. I think the only thing > > that really makes sense for us to do is: > > > > - Read whatever assignments the firmware may have made > > - Keep them unchanged if they seem sensible > > Here I take "sensible" as "it can be successfully claimed" - ie the resource > is allocated in a valid way, though it may not be optimal (eg bridge window > apertures). Yes. But even if platforms assign resources in a way they can be successfully claimed, I don't think platforms should rely on that assignment being unchanged. For example, even if the boot-time configuration is valid, the kernel may need to move things around to deal with hotplug. I know we don't really do that today, but I think we should be able to do it in principle. 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
