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. 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? If we can't guarantee this, we rather fix it now. Some suggestions: a) Make sure code which doesn't have a clear behaviour on ARM is not compiled in and doesn't even try to interpret such tables on ARM (you could just go for the latter but I'm not sure how feasible it is) b) Ensure that the current patches don't support anything other than ACPI 5.1 (6 or later would not be supported; can we get information about which errata update do vendor tables cover?) c) Consider the current ACPI code broken for ARM (rather than feature incomplete) and strongly recommend vendors not to use it Point (a) looks the sanest to me. Point (b) kind of defeats one of the ACPI goals while point (c) would question why we even bother discussing merging now. -- 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
