On Mon, Dec 09, 2013 at 04:12:24AM +0000, Hanjun Guo wrote: > 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. 'Can be used' is one thing, will it really be used is another? I don't think so, it was (well, is) difficult enough to make the transition to FDT, I don't see how ACPI would solve the current issues. I see ACPI as a server distro requirement and there are indeed benefits in abstracting the hardware behind standard description, AML. Of course, this would work even better with probe-able buses like PCIe and I'm pretty sure this would be the case on high-end servers. But even if a server distro like RHEL supports a SoC without PCIe, I would expect them to only provide a single binary Image with CONFIG_PCI enabled. This patch is small enough and allows ACPI build with !CONFIG_PCI for the time being but longer term I would expect such SoCs without PCI to be able to run on a kernel with CONFIG_PCI enabled. -- Catalin -- 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
