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    SubjectRe: [PATCH v3 00/17] Introduce ACPI for ARM64 based on ACPI 5.1
    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



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