On Thu, 11 Sep 2014 16:37:39 +0100, Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > On Thu, Sep 11, 2014 at 02:29:34PM +0100, Grant Likely wrote: > > Regarding the requests to refactor ACPICA to work better for ARM. I > > completely agree that it should be done, but I do not think it should be > > a prerequisite to getting this core support merged. That kind of > > refactoring is far easier to justify when it has immediate improvement > > on the mainline codebase, and it gives us a working baseline to test > > against. Doing it the other way around just makes things harder. > > I have to disagree here. As I said, I'm perfectly fine with refactoring > happening later but I'm not happy with compiling in code with undefined > behaviour on ARM that may actually be executed at run-time. > > I'm being told one of the main advantages of ACPI is forward > compatibility: running older kernels on newer hardware (potentially with > newer ACPI version tables). ACPI 5.1 includes partial support for ARM > but the S and C states are not defined yet. We therefore assume that > hardware vendors deploying servers using ACPI would not provide such > yet to be defined information in ACPI 5.1 tables. We're good on this front. ACPI-future platforms aren't allowed to use new features when booting an older kernel. ACPI has a mechanism to check version numbers. Similarly, when ACPI-future defines those states, the kernel shouldn't expose them to an older platform. > What if in a year time we get ACPI 5.2 or 6 (or an errata update) > covering the S and C states for ARM? I would expect hardware vendors > to take advantage and provide such information in ACPI tables. Can we > guarantee that a kernel with the current ACPI patches wouldn't blow up > when it tries to interpret the new tables? Yes - at least as much as we can guarantee anything in systems programming. g. -- 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
