On 2013-12-7 1:23, Arnd Bergmann wrote: > On Friday 06 December 2013, Tomasz Nowicki wrote: >> On 05.12.2013 23:04, Arnd Bergmann wrote: >>> On Wednesday 04 December 2013, Hanjun Guo wrote: >>>> On 2013年12月04日 00:41, Matthew Garrett wrote: >>>>> Given the number of #ifdefs you're adding, wouldn't it make more sense >>>>> to just add stub functions to include/linux/pci.h? >>>> >>>> Thanks for the suggestion :) >>>> >>>> I can add stub functions in include/linux/pci.h for raw_pci_read()/ >>>> raw_pci_write(), then can remove #ifdefs for acpi_os_read/write_pci_configuration(). >>> >>> Actually I wonder about the usefulness of this patch in either form: Since ACPI >>> on ARM64 is only for servers, I would very much expect them to always come with >>> PCI, either physical host bridges with attached devices, or logical PCI functions >>> used to describe the on-SoC I/O devices. Even in case of virtual machines, you'd >>> normally use PCI as the method to communicate data about the virtio channels. >>> >>> Can you name a realistic use-case where you'd want ACPI but not PCI? >> >> Yes you can describe SoC I/O devices using logical PCI functions only if >> they are on PCI, correct me if I am wrong. Also, devices can be placed >> only on IOMEM (like for ARM SoC) and it is hard to predict which way >> vendors chose. So way don't let it be configurable? ACPI spec says >> nothing like PCI is needed for ACPI, AFAIK. > > You are right that today's ARM SoCs basically never use PCI to describe > internal devices (IIRC VIA VT8500 is an exception, but their PCI was > just a software fabrication). > > However, when we're talking about ACPI on ARM64, that is nothing like classic > ARM SoCs: As Jon Masters mentioned, this is about new server hardware following > a (still secret, but hopefully not much longer) hardware specification that is > explicitly designed to allow interoperability between vendors, so they > must have put some thought into how to make the hardware discoverable. It > seems that they are modeling things after how it's done on x86, and the > only sensible way to have discoverable hardware there is PCI. This is > also what all x86 SoCs do. I think the concern here is that ACPI is only for server platform or not. Since ACPI has lots of content related to power management, I think ACPI can be used for mobile devices and other platform too, not only for ARM servers, and with this patch, we can support both requirement. Thanks Hanjun -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
