On 01/09/2014 10:38 AM, Catalin Marinas wrote:
On 8 January 2014 12:46, Arnd Bergmann arnd@arndb.de wrote:
On Wednesday 08 January 2014, al.stone@linaro.org wrote:
Even though support for X86 in hardware reduced mode is possible, it is NOT enabled. Extensive effort has gone into the Linux kernel so that there is a single kernel image than can run on all x86 hardware; the kernel changes run-time behavior to adapt to the hardware being used. This is not currently possible with the existing ACPICA infrastructure but only presents a problem on achitectures supporting both hardware-reduced and legacy modes of ACPI -- i.e., on x86 only.
Not sure about the logic here: While it's certainly possible to build a kernel that runs on all x86 machines, it's also possible to build one that only runs on some of them when some basic options are turned off. I don't see any difference between that and what we have on ARM64 or the multiplatform subset of ARM32.
Would we ever need !CONFIG_ACPI_REDUCED_HARDWARE_ONLY on ARM or ARM64? If not, we could even make this always on for these archs.
Not that I know of -- and I would hope not. This mode is so much more straightforward that it makes no sense to me to do anything but reduced HW if you have the choice.
I assume you were thinking of something like this in the arch Kconfig file:
config ARM64 .... select ACPI_REDUCED_HARDWARE_ONLY if ACPI ...
But, do let me know if you had something else in mind. I think it does make sense to add so I'll put this in the next version.