On Wednesday 25 July 2007 14:48, Linus Torvalds wrote:ACPI=y SMP=y systems require SUSPEND_SMP=y for system sleep support, and that requires HOTPLUG_CPU=y. Note that ACPI=y SMP=n systems do not need it, and thus will not select HOTPLUG_CPU=y My assumption is that if somebody selects CONFIG_ACPI, that 99% of the time, they intend that to include support for the ACPI hooks for system sleep states. Conversely, supporting the 1% of people who don't want it isn't worth messing with the 99% who do, nor is the burden of yet another config option to maintain and #ifdefs in the code. On UP, they'd get ACPI system sleep support 100% of the time by default, but on SMP this option had become problematic. We used to have this: if ACPI ... config ACPI_SLEEP bool "Sleep States" depends on X86 && (!SMP || SUSPEND_SMP) depends on PM default y So the poster-child failure was i386/defconfig itself... It couldn't support suspend to RAM because it didn't include CONFIG_ACPI_SLEEP. Not trivial for a user to select it when it doesn't even appear on the menu. It doesn't appear because CONFIG_SUSPEND_SMP isn't enabled, but that doesn't appear either -- because CONFIG_HOTPLUG_CPU isn't selected. Most users don't want that. So today we have this: menuconfig ACPI ... select HOTPLUG_CPU if X86 && SMP select SUSPEND_SMP if X86 && SMP Which I think leads to fewer surprises, and less complicated code. (even though using select itself is fraught with peril:-) thanks, -Len -
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