On Thursday, June 02, 2011, MyungJoo Ham wrote:
> A system or a device may need to control suspend/wakeup events. It may
> want to wakeup the system after a predefined amount of time or at a
> predefined event decided while entering suspend for polling or delayed
> work. Then, it may want to enter suspend again if its predefined wakeup
> condition is the only wakeup reason and there is no outstanding events;
> thus, it does not wakeup the userspace unnecessary or unnecessary
> devices and keeps suspended as long as possible (saving the power).
>
> Enabling a system to wakeup after a specified time can be easily
> achieved by using RTC. However, to enter suspend again immediately
> without invoking userland and unrelated devices, we need additional
> features in the suspend framework.
>
> Such need comes from:
>
> 1. Monitoring a critical device status without interrupts that can
> wakeup the system. (in-suspend polling)
> An example is ambient temperature monitoring that needs to shut down
> the system or a specific device function if it is too hot or cold. The
> temperature of a specific device may be needed to be monitored as well;
> e.g., a charger monitors battery temperature in order to stop charging
> if overheated.
>
> 2. Execute critical "delayed work" at suspend.
> A driver or a system/board may have a delayed work (or any similar
> things) that it wants to execute at the requested time.
> For example, some chargers want to check the battery voltage some
> time (e.g., 30 seconds) after the battery is fully charged and the
> charger has stopped. Then, the charger restarts charging if the voltage
> has dropped more than a threshold, which is smaller than "restart-charger"
> voltage, which is a threshold to restart charging regardless of the
> time passed.
>
> This patch allows to add "suspend_again" callback at struct
> platform_suspend_ops and let the "suspend_again" callback return true if
> the system is required to enter suspend again after the current instance
> of wakeup. Device-wise suspend_again implemented at dev_pm_ops or
> syscore is not done because: a) suspend_again feature is usually under
> platform-wise decision and controls the behavior of the whole platform
> and b) There are very limited devices related to the usage cases of
> suspend_again; chargers and temperature sensors are mentioned so far.
>
> With suspend_again callback registered at struct platform_suspend_ops
> suspend_ops in kernel/power/suspend.c with suspend_set_ops by the
> platform, the suspend framework tries to enter suspend again by
> looping suspend_enter() if suspend_again has returned true and there has
> been no errors in the suspending sequence or pending wakeups (by
> pm_wakeup_pending).
>
> Tested at Exynos4-NURI.
>
> Signed-off-by: MyungJoo Ham <myungjoo.ham@xxxxxxxxxxx>
> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
OK, I'll queue it up for 3.1, but I'm still not sure if executing
all of the .suspend_noirq() and .resume_noirq() callbacks in each iteration
of the loop is optimal.
Arguably, we can't do anything more fine grained at the moment, but that's
something to think of in the future.
> --
> Thank you for your valuable comments, Pavel, Rafael, Greg, and others.
>
> Changed from v4:
> - rebased on Linux 3.0 rc1
> - removed partial_suspend/resume because they are not needed, for now.
> Changed from v3:
> - renamed local variable "pm_wkup_pending" to "wakeup_pending".
> pm_wakeup_pending is not used because there is a function with the
> same name.
> Changed from v2:
> - moved (again) from dev_pm_ops to suspend_ops
> - settled suspend_again point at around suspend_enter().
> Changes from v1:
> - moved from syscore to dev_pm_ops
> - added generic ops for subsystems.
> - cleaned up suspend_again code at kernel/power/suspend.
> ---
> include/linux/suspend.h | 8 ++++++++
> kernel/power/suspend.c | 13 ++++++++++---
> 2 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/suspend.h b/include/linux/suspend.h
> index 083ffea..e1e3742 100644
> --- a/include/linux/suspend.h
> +++ b/include/linux/suspend.h
> @@ -92,6 +92,13 @@ typedef int __bitwise suspend_state_t;
> * @enter() and @wake(), even if any of them fails. It is executed after
> * a failing @prepare.
> *
> + * @suspend_again: Returns whether the system should suspend again (true) or
> + * not (false). If the platform wants to poll sensors or execute some
> + * code during suspended without invoking userspace and most of devices,
> + * suspend_again callback is the place assuming that periodic-wakeup or
> + * alarm-wakeup is already setup. This allows to execute some codes while
> + * being kept suspended in the view of userland and devices.
> + *
> * @end: Called by the PM core right after resuming devices, to indicate to
> * the platform that the system has returned to the working state or
> * the transition to the sleep state has been aborted.
> @@ -113,6 +120,7 @@ struct platform_suspend_ops {
> int (*enter)(suspend_state_t state);
> void (*wake)(void);
> void (*finish)(void);
> + bool (*suspend_again)(void);
> void (*end)(void);
> void (*recover)(void);
> };
> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> index 1c41ba2..d8a6c51 100644
> --- a/kernel/power/suspend.c
> +++ b/kernel/power/suspend.c
> @@ -128,10 +128,12 @@ void __attribute__ ((weak)) arch_suspend_enable_irqs(void)
> /**
> * suspend_enter - enter the desired system sleep state.
> * @state: state to enter
> + * @wakeup_pending: indicates that the power transition in progress
> + * should be aborted.
This should be just one line, otherwise kerneldoc will have problems with it.
I'll fix it up.
Thanks,
Rafael
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