On Wednesday, June 15, 2011, Rafael J. Wysocki wrote: > On Tuesday, June 14, 2011, Colin Cross wrote: > > On Tue, Jun 14, 2011 at 2:34 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > > On Tuesday, June 14, 2011, Colin Cross wrote: > > >> On Tue, Jun 14, 2011 at 2:00 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > >> > On Monday, June 13, 2011, Colin Cross wrote: > > >> >> On Mon, Jun 13, 2011 at 11:37 AM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > >> >> > On Monday, June 13, 2011, Colin Cross wrote: > > >> >> >> This patch set tries to address Russell's concerns with platform > > >> >> >> pm code calling into the driver for every block in the Cortex A9s > > >> >> >> during idle, hotplug, and suspend. The first patch adds cpu pm > > >> >> >> notifiers that can be called by platform code, the second uses > > >> >> >> the notifier to save and restore the GIC state, and the third > > >> >> >> saves the VFP state. > > >> >> >> > > >> >> >> The notifiers are used for two types of events, CPU PM events and > > >> >> >> CPU complex PM events. CPU PM events are used to save and restore > > >> >> >> per-cpu context when a single CPU is preparing to enter or has > > >> >> >> just exited a low power state. For example, the VFP saves the > > >> >> >> last thread context, and the GIC saves banked CPU registers. > > >> >> >> > > >> >> >> CPU complex events are used after all the CPUs in a power domain > > >> >> >> have been prepared for the low power state. The GIC uses these > > >> >> >> events to save global register state. > > >> >> >> > > >> >> >> Platforms that call the cpu_pm APIs must select > > >> >> >> CONFIG_ARCH_USES_CPU_PM > > >> >> >> > > >> >> >> L2 cache is not covered by this patch set, as the determination > > >> >> >> of when the L2 is reset and when it is retained is > > >> >> >> platform-specific, and most of the APIs necessary are already > > >> >> >> present. > > >> >> >> > > >> >> >> arch/arm/Kconfig | 7 ++ > > >> >> >> arch/arm/common/gic.c | 212 +++++++++++++++++++++++++++++++++++++++++ > > >> >> >> arch/arm/include/asm/cpu_pm.h | 54 +++++++++++ > > >> >> >> arch/arm/kernel/Makefile | 1 + > > >> >> >> arch/arm/kernel/cpu_pm.c | 181 +++++++++++++++++++++++++++++++++++ > > >> >> > > > >> >> > Is there any reason why this has to be ARM-specific? There are other > > >> >> > architectures where this kind of feature might make sense (SH and > > >> >> > powerpc at least). > > >> >> > > >> >> Nothing other than there are currently no adaptations for any drivers > > >> >> besides ARM, but I can move it somewhere outside ARM. Any suggestions > > >> >> where? > > >> > > > >> > Well, there is kernel/cpu.c. It contains mostly CPU hotplug and PM > > >> > code at the moment, so it looks like a good place. > > >> > > >> OK, I'll look at moving it there. > > >> > > >> >> > Besides, is there any overlap between this feature and the CPU hotplug > > >> >> > notifiers? > > >> >> > > >> >> I don't think so - the hotplug notifiers are used when a CPU is being > > >> >> removed from the system, so no saving and restoring is necessary - the > > >> >> CPU will be rebooted from scratch. They are used by systems outside > > >> >> the CPU that need to know that a CPU no longer exists. > > >> >> > > >> >> CPU PM notifiers are used when a CPU is going through reset in a way > > >> >> that should be transparent to most of the system. > > >> > > > >> > Do I guess correctly that you mean cpuidle? > > >> > > >> cpuidle is the major user, but primary CPUs in suspend have to save > > >> and restore the same blocks, and tend to use the same platform sleep > > >> code as idle, so it's logical to use the notifiers for both. On the > > >> other hand, some drivers that would use cpu_pm notifiers already use > > >> syscore ops to handle suspend and resume (like vfp) - maybe these > > >> notifiers should only be used in cpuidle, and syscore ops added to the > > >> gic driver? I could also convert the notifiers to new syscore_ops - > > >> cpu_idle, cpu_unidle, cpu_cluster_idle, cpu_cluster_unidle, but I > > >> don't know how well that fits in to the intention for syscore. > > > > > > Basically, syscore_ops deal with the situation during system suspend > > > when all CPUs but one have been switched off (through CPU hotplug) > > > and interrupts are off on the only active CPU. If there's anything > > > you need to do at this point, syscore_ops is the right thing to use. > > > And analogously for system resume. > > > > > > Moreover, for system suspend switching off the "boot" CPU (i.e. the only one > > > that remains active through the whole sequence) should really be the last > > > thing done, everything else should have been handled through syscore_ops > > > before. > > > > Yes, but what to do with idle, which generally needs to do the exact > > same things as handled in some syscore ops? Extend syscore ops, or > > add the new notifier, and each driver can implement both syscore and > > cpu_pm listeners (and probably call the same helper function to handle > > both)? > > Good question. I don't think I have a good answer to it at the moment, need > to ponder that a bit more. So, it looks like system suspend only needs those things because it uses (a part of) the cpuidle infrastructure to put the CPU into a low-power state. Thus from the system suspend point of view, they are parts of the "switch the CPU off" operation, so syscore_ops don't seem to be suitable for doing them. That said, they seem to belong to cpuidle rather than to "general PM". Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
