On Mon, Sep 15, 2014 at 11:48:00PM +0100, Grant Likely wrote: > On Mon, 15 Sep 2014 10:15:16 +0100, Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > On Mon, Sep 15, 2014 at 05:31:16AM +0100, Grant Likely wrote: > > > 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. > > > > Do you mean ACPI-future firmware should not provide new information to > > older kernels? > > I mean that ACPI has the mechanism so that the platform (via AML) > doesn't try to do things that the OS doesn't understand. AML methods are > to use the \_REV object to determine whether or not it can use a > feature. If, for example, the _REV is 5, then the AML must switch itself > to code paths that don't use ACPI 6 features. So you are talking about AML code paths and from what I understand they should be fine. However, what I'm talking about is _kernel_ code paths and functions like acpi_suspend_enter(). Do you mean this function can only be called as a result of some AML execution (it doesn't look so to me)? If not, what guarantees do we have that ACPI-future tables exposed to an older kernel would not trigger this kernel code path (if compiled in)? -- 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
