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.
Regards,
Sudeep
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