Messages in this thread Patch in this message | | | From | Kevin Hilman <> | Subject | Re: [PATCH 1/3] ARM: Add cpu power management notifiers | Date | Mon, 13 Jun 2011 15:17:57 -0700 |
| |
Colin Cross <ccross@android.com> writes:
> During some CPU power modes entered during idle, hotplug and > suspend, peripherals located in the CPU power domain, such as > the GIC and VFP, may be powered down. Add a notifier chain > that allows drivers for those peripherals to be notified > before and after they may be reset. > > Signed-off-by: Colin Cross <ccross@android.com>
This is great, thanks!
I had hacked up something OMAP-specific a while back to do something similar, and have been meaning to make it more generic, so this is perfect. Also, if it is moved outside ARM, note that x86_64 has a idle_notifier infrastructure that is somewhat similar, and if you're motivated, it should probably be converted to this as well. See arch/x86/kernel/process_64.c.
Also, for the sake of the comments/changelog, the usefulness of these notifiers is not limited to low-power states where power is off and IP blocks may be reset. It could be considered as simply a generic notification mechanism for any CPU PM transitions.
On OMAP we have other peripherals (not in the CPU power domain) where we need to control their PM transitions in relation to the CPU PM transitions so the notifiers are useful for any low-power state transition of the CPU(s). The drivers for these peripherals use runtime PM in their CPU PM notifiers to trigger the device PM transitions. (The drivers must use the synchronous versions of the runtime PM get/put calls with device in pm_runtime_irq_safe() mode.)
In this series, I don't see any calls to cpu_[complex_]pm_[enter|exit](). Based on that, I assume you prefer to leave it up to platform-specific idle/PM code to place these calls. Or, do you plan to have this triggered by generic CPUidle, suspend/resume and/or hotplug code? At least on OMAP, I prefer having the calls in platform-specific code.
I have a minor enhancement request. The notifier callbacks provide for passing a void * through the notifier chain. Could you add a way for a void * to be registered at cpu_pm_register_notifier() time and that would be passed through the notifier call chain? This would allow using the same struct notifier_block and callback for multiple instances of the same IP, and the instances could be differentiated in the callback using the void *.
Also, FWIW I tested this on OMAP3 (Cortex-A8 UP) using cpu_pm_enter/exit() in the code path shared between idle and suspend. I successfully triggered PM transitions in non-CPU power-domain peripherals, and it worked great.
Some other minor comments below...
[...]
> diff --git a/arch/arm/kernel/cpu_pm.c b/arch/arm/kernel/cpu_pm.c > new file mode 100644 > index 0000000..48a5b53 > --- /dev/null > +++ b/arch/arm/kernel/cpu_pm.c > @@ -0,0 +1,181 @@ > +/* > + * Copyright (C) 2011 Google, Inc. > + * > + * Author: > + * Colin Cross <ccross@android.com> > + * > + * This software is licensed under the terms of the GNU General Public > + * License version 2, as published by the Free Software Foundation, and > + * may be copied, distributed, and modified under those terms. > + * > + * This program is distributed in the hope that it will be useful, > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > + * GNU General Public License for more details. > + * > + */ > + > +#include <linux/kernel.h> > +#include <linux/module.h> > +#include <linux/notifier.h> > +#include <linux/spinlock.h> > + > +#include <asm/cpu_pm.h> > + > +/* > + * When a CPU goes to a low power state that turns off power to the CPU's > + * power domain, the contents of some blocks (floating point coprocessors, > + * interrutp controllers, caches, timers) in the same power domain can typo: interrutp
> + * be lost. The cpm_pm notifiers provide a method for platform idle, suspend, > + * and hotplug implementations to notify the drivers for these blocks that > + * they may be reset. > + * > + * All cpu_pm notifications must be called with interrupts disabled. > + * > + * The notifications are split into two classes, CPU notifications and CPU > + * complex notifications. > + * > + * CPU notifications apply to a single CPU, and must be called on the affected > + * CPU. They are used to save per-cpu context for affected blocks. > + * > + * CPU complex notifications apply to all CPUs in a single power domain. They > + * are used to save any global context for affected blocks, and must be called > + * after all the CPUs in the power domain have been notified of the low power > + * state. > + * > + */
Not directly related to this series, but I'm a bit confused on terminology.
I've seen both 'CPU complex' and 'CPU cluster' used in ARM SMP land, but haven't seen precise definitions of either. Does one imply all CPUs, and the other imply all CPUs in the same power domain?
Kevin
| |