On Thu, Sep 11, 2014 at 04:57:24PM +0100, Sudeep Holla wrote: > > > On 11/09/14 16:37, Catalin Marinas 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. > > > >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) > > This what we have suggested in past especially for this S-state support. > Currently the core acpi code compiles in sleep support unconditionally. > That doesn't mean we need to do the same on ARM64, we can easily make > sure that's not enabled for ARM64 until we have clarification on how to > support them on ARM in ACPI specification. > > I just pointed out at one "out of spec" workaround done for x86 > "unconditionally" in the code just to tell that it won't work on ARM. > That shouldn't be misunderstood as demand for refactoring as we have no > clue how S-state would look on ARM to take up any such task. > For the sleep.c case I worked on this and sent some updates to Hanjun so it should be compiled out in the next version of the patches. Graeme -- 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
