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@arm.com 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@arm.com 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)?