Re: [PATCH] cpufreq: suspend/resume governors with PM notifiers

From: Rafael J. Wysocki
Date: Fri Nov 15 2013 - 19:12:29 EST

On Friday, November 15, 2013 03:42:29 PM Viresh Kumar wrote:
> This patch adds PM notifiers for handling suspend/resume of cpufreq governors.
> This is required for early suspend and late resume of governors.
>
> There are multiple reasons that support this patch:
> - Firstly it looks very much logical to stop governors when we know we are going
> into suspend. But the question is when? Is PM notifiers the right place?
> Following reasons are the supporting hands for this decision.
> - Nishanth Menon (TI) found an interesting problem on his platform, OMAP. His board
> wasn't working well with suspend/resume as calls for removing non-boot CPUs
> was turning out into a call to drivers ->target() which then tries to play
> with regulators. But regulators and their I2C bus were already suspended and
> this resulted in a failure. This is why we need a PM notifier here.
> - Lan Tianyu (Intel) & Jinhyuk Choi (Broadcom) found another issue where
> tunables configuration for clusters/sockets with non-boot CPUs was getting
> lost after suspend/resume, as we were notifying governors with
> CPUFREQ_GOV_POLICY_EXIT on removal of the last cpu for that policy and so
> deallocating memory for tunables.
>
> All above problems get fixed with having a PM notifier in place which will stop
> any operation on governor. Hence no need to do any special handling of variables
> like (frozen) in suspend/resume paths.

Will cpufreq work during system-wide power transitions (suspend/resume etc.)
after this? In particular, what about hibernation?

> Reported-by: Lan Tianyu <tianyu.lan@xxxxxxxxx>
> Reported-by: Nishanth Menon <nm@xxxxxx>
> Reported-by: Jinhyuk Choi <jinchoi@xxxxxxxxxxxx>
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
>
> Hi Guys,
>
> Can you please verify if this fixes issues reported by you? I have tested this
> for multiple suspend-resumes on my thinkpad. It doesn't crash :)
>
> drivers/cpufreq/cpufreq.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 63 insertions(+)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 02d534d..c87ced9 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -26,6 +26,7 @@
> #include <linux/module.h>
> #include <linux/mutex.h>
> #include <linux/slab.h>
> +#include <linux/suspend.h>
> #include <linux/syscore_ops.h>
> #include <linux/tick.h>
> #include <trace/events/power.h>
> @@ -47,6 +48,9 @@ static LIST_HEAD(cpufreq_policy_list);
> static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor);
> #endif
>
> +/* Flag to suspend/resume CPUFreq governors */
> +static bool cpufreq_suspended;
> +
> static inline bool has_target(void)
> {
> return cpufreq_driver->target_index || cpufreq_driver->target;
> @@ -1462,6 +1466,54 @@ static struct subsys_interface cpufreq_interface = {
> .remove_dev = cpufreq_remove_dev,
> };
>
> +/*
> + * PM Notifier for suspending governors as some platforms can't change frequency
> + * after this point in suspend cycle. Because some of the devices (like: i2c,
> + * regulators, etc) they use for changing frequency are suspended quickly after
> + * this point.
> + */
> +static int cpufreq_pm_notify(struct notifier_block *nb, unsigned long action,
> + void *data)
> +{
> + struct cpufreq_policy *policy;
> + unsigned long flags;
> +
> + if (!has_target())
> + return NOTIFY_OK;
> +
> + if (action == PM_SUSPEND_PREPARE) {
> + pr_debug("%s: Suspending Governors\n", __func__);
> +
> + list_for_each_entry(policy, &cpufreq_policy_list, policy_list)
> + if (__cpufreq_governor(policy, CPUFREQ_GOV_STOP))
> + pr_err("%s: Failed to stop governor for policy: %p\n",
> + __func__, policy);
> +
> + write_lock_irqsave(&cpufreq_driver_lock, flags);
> + cpufreq_suspended = true;
> + write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> + } else if (action == PM_POST_SUSPEND) {
> + pr_debug("%s: Resuming Governors\n", __func__);
> +
> + write_lock_irqsave(&cpufreq_driver_lock, flags);
> + cpufreq_suspended = false;
> + write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> +
> + list_for_each_entry(policy, &cpufreq_policy_list, policy_list)
> + if (__cpufreq_governor(policy, CPUFREQ_GOV_START) ||
> + __cpufreq_governor(policy,
> + CPUFREQ_GOV_LIMITS))
> + pr_err("%s: Failed to start governor for policy: %p\n",
> + __func__, policy);
> + }
> +
> + return NOTIFY_OK;
> +}
> +
> +static struct notifier_block cpufreq_pm_notifier = {
> + .notifier_call = cpufreq_pm_notify,
> +};
> +
> /**
> * cpufreq_bp_suspend - Prepare the boot CPU for system suspend.
> *
> @@ -1752,6 +1804,8 @@ EXPORT_SYMBOL_GPL(cpufreq_driver_target);
> static int __cpufreq_governor(struct cpufreq_policy *policy,
> unsigned int event)
> {
> + unsigned long flags;
> + bool is_suspended;
> int ret;
>
> /* Only must be defined when default governor is known to have latency
> @@ -1764,6 +1818,14 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
> struct cpufreq_governor *gov = NULL;
> #endif
>
> + /* Don't start any governor operations if we are entering suspend */
> + read_lock_irqsave(&cpufreq_driver_lock, flags);
> + is_suspended = cpufreq_suspended;
> + read_unlock_irqrestore(&cpufreq_driver_lock, flags);
> +
> + if (is_suspended)
> + return 0;
> +
> if (policy->governor->max_transition_latency &&
> policy->cpuinfo.transition_latency >
> policy->governor->max_transition_latency) {
> @@ -2222,6 +2284,7 @@ static int __init cpufreq_core_init(void)
> cpufreq_global_kobject = kobject_create();
> BUG_ON(!cpufreq_global_kobject);
> register_syscore_ops(&cpufreq_syscore_ops);
> + register_pm_notifier(&cpufreq_pm_notifier);
>
> return 0;
> }
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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