[CPUFREQ] ARM Exynos4210 PM/Suspend compatibility with different bootloaders

We have various bootloaders for Exynos4210 machines. Some of they
set the ARM core frequency at boot time even when the boot is a resume
from suspend-to-RAM. Such changes may create inconsistency in the
data of CPUFREQ driver and have incurred hang issues with suspend-to-RAM.

This patch enables to save and restore CPU frequencies with pm-notifier and
sets the frequency at the initial (boot-time) value so that there wouldn't
be any inconsistency between bootloader and kernel. This patch does not
use CPUFREQ's suspend/resume callbacks because they are syscore-ops, which
do not allow to use mutex that is being used by regulators that are used by
the target function.

This also prevents any CPUFREQ transitions during suspend-resume context,
which could be dangerous at noirq-context along with regulator framework.

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Dave Jones <davej@redhat.com>

1 files changed, 102 insertions, 4 deletions

diff --git a/drivers/cpufreq/exynos4210-cpufreq.c b/drivers/cpufreq/exynos4210-cpufreq.c
index 6f887573ce94..ab9741fab92e 100644
--- a/drivers/cpufreq/exynos4210-cpufreq.c
+++ b/drivers/cpufreq/exynos4210-cpufreq.c
@@ -17,6 +17,8 @@
 #include <linux/slab.h>
 #include <linux/regulator/consumer.h>
 #include <linux/cpufreq.h>
+#include <linux/notifier.h>
+#include <linux/suspend.h>
 
 #include <mach/map.h>
 #include <mach/regs-clock.h>
@@ -36,6 +38,10 @@ static struct regulator *int_regulator;
 static struct cpufreq_freqs freqs;
 static unsigned int memtype;
 
+static unsigned int locking_frequency;
+static bool frequency_locked;
+static DEFINE_MUTEX(cpufreq_lock);
+
 enum exynos4_memory_type {
         DDR2 = 4,
         LPDDR2,
@@ -405,22 +411,32 @@ static int exynos4_target(struct cpufreq_policy *policy,
 {
         unsigned int index, old_index;
         unsigned int arm_volt, int_volt;
+        int err = -EINVAL;
 
         freqs.old = exynos4_getspeed(policy->cpu);
 
+        mutex_lock(&cpufreq_lock);
+
+        if (frequency_locked && target_freq != locking_frequency) {
+                err = -EAGAIN;
+                goto out;
+        }
+
         if (cpufreq_frequency_table_target(policy, exynos4_freq_table,
                                            freqs.old, relation, &old_index))
-                return -EINVAL;
+                goto out;
 
         if (cpufreq_frequency_table_target(policy, exynos4_freq_table,
                                            target_freq, relation, &index))
-                return -EINVAL;
+                goto out;
+
+        err = 0;
 
         freqs.new = exynos4_freq_table[index].frequency;
         freqs.cpu = policy->cpu;
 
         if (freqs.new == freqs.old)
-                return 0;
+                goto out;
 
         /* get the voltage value */
         arm_volt = exynos4_volt_table[index].arm_volt;
@@ -447,10 +463,16 @@ static int exynos4_target(struct cpufreq_policy *policy,
 
         cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);
 
-        return 0;
+out:
+        mutex_unlock(&cpufreq_lock);
+        return err;
 }
 
 #ifdef CONFIG_PM
+/*
+ * These suspend/resume are used as syscore_ops, it is already too
+ * late to set regulator voltages at this stage.
+ */
 static int exynos4_cpufreq_suspend(struct cpufreq_policy *policy)
 {
         return 0;
@@ -462,6 +484,78 @@ static int exynos4_cpufreq_resume(struct cpufreq_policy *policy)
 }
 #endif
 
+/**
+ * exynos4_cpufreq_pm_notifier - block CPUFREQ's activities in suspend-resume
+ *                      context
+ * @notifier
+ * @pm_event
+ * @v
+ *
+ * While frequency_locked == true, target() ignores every frequency but
+ * locking_frequency. The locking_frequency value is the initial frequency,
+ * which is set by the bootloader. In order to eliminate possible
+ * inconsistency in clock values, we save and restore frequencies during
+ * suspend and resume and block CPUFREQ activities. Note that the standard
+ * suspend/resume cannot be used as they are too deep (syscore_ops) for
+ * regulator actions.
+ */
+static int exynos4_cpufreq_pm_notifier(struct notifier_block *notifier,
+                                       unsigned long pm_event, void *v)
+{
+        struct cpufreq_policy *policy = cpufreq_cpu_get(0); /* boot CPU */
+        static unsigned int saved_frequency;
+        unsigned int temp;
+
+        mutex_lock(&cpufreq_lock);
+        switch (pm_event) {
+        case PM_SUSPEND_PREPARE:
+                if (frequency_locked)
+                        goto out;
+                frequency_locked = true;
+
+                if (locking_frequency) {
+                        saved_frequency = exynos4_getspeed(0);
+
+                        mutex_unlock(&cpufreq_lock);
+                        exynos4_target(policy, locking_frequency,
+                                       CPUFREQ_RELATION_H);
+                        mutex_lock(&cpufreq_lock);
+                }
+
+                break;
+        case PM_POST_SUSPEND:
+
+                if (saved_frequency) {
+                        /*
+                         * While frequency_locked, only locking_frequency
+                         * is valid for target(). In order to use
+                         * saved_frequency while keeping frequency_locked,
+                         * we temporarly overwrite locking_frequency.
+                         */
+                        temp = locking_frequency;
+                        locking_frequency = saved_frequency;
+
+                        mutex_unlock(&cpufreq_lock);
+                        exynos4_target(policy, locking_frequency,
+                                       CPUFREQ_RELATION_H);
+                        mutex_lock(&cpufreq_lock);
+
+                        locking_frequency = temp;
+                }
+
+                frequency_locked = false;
+                break;
+        }
+out:
+        mutex_unlock(&cpufreq_lock);
+
+        return NOTIFY_OK;
+}
+
+static struct notifier_block exynos4_cpufreq_nb = {
+        .notifier_call = exynos4_cpufreq_pm_notifier,
+};
+
 static int exynos4_cpufreq_cpu_init(struct cpufreq_policy *policy)
 {
         int ret;
@@ -522,6 +616,8 @@ static int __init exynos4_cpufreq_init(void)
         if (IS_ERR(cpu_clk))
                 return PTR_ERR(cpu_clk);
 
+        locking_frequency = exynos4_getspeed(0);
+
         moutcore = clk_get(NULL, "moutcore");
         if (IS_ERR(moutcore))
                 goto out;
@@ -561,6 +657,8 @@ static int __init exynos4_cpufreq_init(void)
                 printk(KERN_DEBUG "%s: memtype= 0x%x\n", __func__, memtype);
         }
 
+        register_pm_notifier(&exynos4_cpufreq_nb);
+
         return cpufreq_register_driver(&exynos4_driver);
 
 out: