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Date: Fri, 22 Nov 2013 13:33:10 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: linaro-kernel@...ts.linaro.org, patches@...aro.org,
cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org, tianyu.lan@...el.com, nm@...com,
jinchoi@...adcom.com, sebastian.capella@...aro.org
Subject: Re: [PATCH V2 1/2] cpufreq: suspend governors on system suspend/hibernate
On Friday, November 22, 2013 04:59:48 PM Viresh Kumar wrote:
> This patch adds cpufreq callbacks to dpm_{suspend|resume}_noirq() for handling
> suspend/resume of cpufreq governors. This is required for early suspend and late
> resume of governors.
>
> There are multiple problems that are fixed by this patch:
> - 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.
>
> Reported-by: Lan Tianyu <tianyu.lan@...el.com>
> Reported-by: Nishanth Menon <nm@...com>
> Reported-by: Jinhyuk Choi <jinchoi@...adcom.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> drivers/base/power/main.c | 3 +++
> drivers/cpufreq/cpufreq.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/cpufreq.h | 3 +++
> 3 files changed, 68 insertions(+)
>
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index c12e9b9..0fbe792 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -29,6 +29,7 @@
> #include <linux/async.h>
> #include <linux/suspend.h>
> #include <trace/events/power.h>
> +#include <linux/cpufreq.h>
> #include <linux/cpuidle.h>
> #include <linux/timer.h>
>
> @@ -540,6 +541,7 @@ static void dpm_resume_noirq(pm_message_t state)
> dpm_show_time(starttime, state, "noirq");
> resume_device_irqs();
> cpuidle_resume();
> + cpufreq_resume();
> }
>
> /**
> @@ -955,6 +957,7 @@ static int dpm_suspend_noirq(pm_message_t state)
> ktime_t starttime = ktime_get();
> int error = 0;
>
> + cpufreq_suspend();
> cpuidle_pause();
> suspend_device_irqs();
> mutex_lock(&dpm_list_mtx);
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 02d534d..540bd87 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,
> };
>
> +/*
> + * Callbacks for suspending/resuming 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.
> + */
> +void cpufreq_suspend(void)
> +{
> + struct cpufreq_policy *policy;
> + unsigned long flags;
> +
> + if (!has_target())
> + return;
> +
> + 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);
The locking here is pointless. It doesn't prevent any race conditions
from happening.
> +}
> +
> +void cpufreq_resume(void)
> +{
> + struct cpufreq_policy *policy;
> + unsigned long flags;
> +
> + if (!has_target())
> + return;
> +
> + pr_debug("%s: Resuming Governors\n", __func__);
> +
> + write_lock_irqsave(&cpufreq_driver_lock, flags);
> + cpufreq_suspended = false;
> + write_unlock_irqrestore(&cpufreq_driver_lock, flags);
Same here.
> +
> + 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);
> +}
> +
> /**
> * 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);
And same here.
> +
> + if (is_suspended)
And you can check cpufreq_suspended directly here.
> + return 0;
> +
> if (policy->governor->max_transition_latency &&
> policy->cpuinfo.transition_latency >
> policy->governor->max_transition_latency) {
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index dc196bb..6d93f91 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -255,6 +255,9 @@ struct cpufreq_driver {
> int cpufreq_register_driver(struct cpufreq_driver *driver_data);
> int cpufreq_unregister_driver(struct cpufreq_driver *driver_data);
>
> +void cpufreq_suspend(void);
> +void cpufreq_resume(void);
> +
> const char *cpufreq_get_current_driver(void);
>
> static inline void cpufreq_verify_within_limits(struct cpufreq_policy *policy,
Thanks!
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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