PM / devfreq: exynos4_bus: honor RCU lock usage

OPP pointers cannot be expected to be valid beyond the boundary
of rcu_read_lock and rcu_read_unlock. Unfortunately, the current
exynos4 busfreq driver does not honor the usage constraint and stores
the OPP pointer in struct busfreq_data. This could potentially
become invalid later such as: across devfreq opp change decisions,
resulting in unpredictable behavior.

To fix this, we introduce a busfreq specific busfreq_opp_info
structure which is used to handle OPP information. OPP information
is de-referenced to voltage and frequency pairs as needed into
busfreq_opp_info structure and used as needed.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 67 insertions, 27 deletions

diff --git a/drivers/devfreq/exynos4_bus.c b/drivers/devfreq/exynos4_bus.c
index 80c745e83082..46d94e9e95b5 100644
--- a/drivers/devfreq/exynos4_bus.c
+++ b/drivers/devfreq/exynos4_bus.c
@@ -73,6 +73,16 @@ enum busclk_level_idx {
 #define EX4210_LV_NUM   (LV_2 + 1)
 #define EX4x12_LV_NUM   (LV_4 + 1)
 
+/**
+ * struct busfreq_opp_info - opp information for bus
+ * @rate:       Frequency in hertz
+ * @volt:       Voltage in microvolts corresponding to this OPP
+ */
+struct busfreq_opp_info {
+        unsigned long rate;
+        unsigned long volt;
+};
+
 struct busfreq_data {
         enum exynos4_busf_type type;
         struct device *dev;
@@ -80,7 +90,7 @@ struct busfreq_data {
         bool disabled;
         struct regulator *vdd_int;
         struct regulator *vdd_mif; /* Exynos4412/4212 only */
-        struct opp *curr_opp;
+        struct busfreq_opp_info curr_oppinfo;
         struct exynos4_ppmu dmc[2];
 
         struct notifier_block pm_notifier;
@@ -296,13 +306,14 @@ static unsigned int exynos4x12_clkdiv_sclkip[][3] = {
 };
 
 
-static int exynos4210_set_busclk(struct busfreq_data *data, struct opp *opp)
+static int exynos4210_set_busclk(struct busfreq_data *data,
+                                 struct busfreq_opp_info *oppi)
 {
         unsigned int index;
         unsigned int tmp;
 
         for (index = LV_0; index < EX4210_LV_NUM; index++)
-                if (opp_get_freq(opp) == exynos4210_busclk_table[index].clk)
+                if (oppi->rate == exynos4210_busclk_table[index].clk)
                         break;
 
         if (index == EX4210_LV_NUM)
@@ -361,13 +372,14 @@ static int exynos4210_set_busclk(struct busfreq_data *data, struct opp *opp)
         return 0;
 }
 
-static int exynos4x12_set_busclk(struct busfreq_data *data, struct opp *opp)
+static int exynos4x12_set_busclk(struct busfreq_data *data,
+                                 struct busfreq_opp_info *oppi)
 {
         unsigned int index;
         unsigned int tmp;
 
         for (index = LV_0; index < EX4x12_LV_NUM; index++)
-                if (opp_get_freq(opp) == exynos4x12_mifclk_table[index].clk)
+                if (oppi->rate == exynos4x12_mifclk_table[index].clk)
                         break;
 
         if (index == EX4x12_LV_NUM)
@@ -576,11 +588,12 @@ static int exynos4x12_get_intspec(unsigned long mifclk)
         return -EINVAL;
 }
 
-static int exynos4_bus_setvolt(struct busfreq_data *data, struct opp *opp,
-                               struct opp *oldopp)
+static int exynos4_bus_setvolt(struct busfreq_data *data,
+                               struct busfreq_opp_info *oppi,
+                               struct busfreq_opp_info *oldoppi)
 {
         int err = 0, tmp;
-        unsigned long volt = opp_get_voltage(opp);
+        unsigned long volt = oppi->volt;
 
         switch (data->type) {
         case TYPE_BUSF_EXYNOS4210:
@@ -595,11 +608,11 @@ static int exynos4_bus_setvolt(struct busfreq_data *data, struct opp *opp,
                 if (err)
                         break;
 
-                tmp = exynos4x12_get_intspec(opp_get_freq(opp));
+                tmp = exynos4x12_get_intspec(oppi->rate);
                 if (tmp < 0) {
                         err = tmp;
                         regulator_set_voltage(data->vdd_mif,
-                                              opp_get_voltage(oldopp),
+                                              oldoppi->volt,
                                               MAX_SAFEVOLT);
                         break;
                 }
@@ -609,7 +622,7 @@ static int exynos4_bus_setvolt(struct busfreq_data *data, struct opp *opp,
                 /*  Try to recover */
                 if (err)
                         regulator_set_voltage(data->vdd_mif,
-                                              opp_get_voltage(oldopp),
+                                              oldoppi->volt,
                                               MAX_SAFEVOLT);
                 break;
         default:
@@ -626,17 +639,26 @@ static int exynos4_bus_target(struct device *dev, unsigned long *_freq,
         struct platform_device *pdev = container_of(dev, struct platform_device,
                                                     dev);
         struct busfreq_data *data = platform_get_drvdata(pdev);
-        struct opp *opp = devfreq_recommended_opp(dev, _freq, flags);
-        unsigned long freq = opp_get_freq(opp);
-        unsigned long old_freq = opp_get_freq(data->curr_opp);
+        struct opp *opp;
+        unsigned long freq;
+        unsigned long old_freq = data->curr_oppinfo.rate;
+        struct busfreq_opp_info new_oppinfo;
 
-        if (IS_ERR(opp))
+        rcu_read_lock();
+        opp = devfreq_recommended_opp(dev, _freq, flags);
+        if (IS_ERR(opp)) {
+                rcu_read_unlock();
                 return PTR_ERR(opp);
+        }
+        new_oppinfo.rate = opp_get_freq(opp);
+        new_oppinfo.volt = opp_get_voltage(opp);
+        rcu_read_unlock();
+        freq = new_oppinfo.rate;
 
         if (old_freq == freq)
                 return 0;
 
-        dev_dbg(dev, "targetting %lukHz %luuV\n", freq, opp_get_voltage(opp));
+        dev_dbg(dev, "targetting %lukHz %luuV\n", freq, new_oppinfo.volt);
 
         mutex_lock(&data->lock);
 
@@ -644,17 +666,18 @@ static int exynos4_bus_target(struct device *dev, unsigned long *_freq,
                 goto out;
 
         if (old_freq < freq)
-                err = exynos4_bus_setvolt(data, opp, data->curr_opp);
+                err = exynos4_bus_setvolt(data, &new_oppinfo,
+                                          &data->curr_oppinfo);
         if (err)
                 goto out;
 
         if (old_freq != freq) {
                 switch (data->type) {
                 case TYPE_BUSF_EXYNOS4210:
-                        err = exynos4210_set_busclk(data, opp);
+                        err = exynos4210_set_busclk(data, &new_oppinfo);
                         break;
                 case TYPE_BUSF_EXYNOS4x12:
-                        err = exynos4x12_set_busclk(data, opp);
+                        err = exynos4x12_set_busclk(data, &new_oppinfo);
                         break;
                 default:
                         err = -EINVAL;
@@ -664,11 +687,12 @@ static int exynos4_bus_target(struct device *dev, unsigned long *_freq,
                 goto out;
 
         if (old_freq > freq)
-                err = exynos4_bus_setvolt(data, opp, data->curr_opp);
+                err = exynos4_bus_setvolt(data, &new_oppinfo,
+                                          &data->curr_oppinfo);
         if (err)
                 goto out;
 
-        data->curr_opp = opp;
+        data->curr_oppinfo = new_oppinfo;
 out:
         mutex_unlock(&data->lock);
         return err;
@@ -702,7 +726,7 @@ static int exynos4_bus_get_dev_status(struct device *dev,
 
         exynos4_read_ppmu(data);
         busier_dmc = exynos4_get_busier_dmc(data);
-        stat->current_frequency = opp_get_freq(data->curr_opp);
+        stat->current_frequency = data->curr_oppinfo.rate;
 
         if (busier_dmc)
                 addr = S5P_VA_DMC1;
@@ -933,6 +957,7 @@ static int exynos4_busfreq_pm_notifier_event(struct notifier_block *this,
         struct busfreq_data *data = container_of(this, struct busfreq_data,
                                                  pm_notifier);
         struct opp *opp;
+        struct busfreq_opp_info new_oppinfo;
         unsigned long maxfreq = ULONG_MAX;
         int err = 0;
 
@@ -943,18 +968,29 @@ static int exynos4_busfreq_pm_notifier_event(struct notifier_block *this,
 
                 data->disabled = true;
 
+                rcu_read_lock();
                 opp = opp_find_freq_floor(data->dev, &maxfreq);
+                if (IS_ERR(opp)) {
+                        rcu_read_unlock();
+                        dev_err(data->dev, "%s: unable to find a min freq\n",
+                                __func__);
+                        return PTR_ERR(opp);
+                }
+                new_oppinfo.rate = opp_get_freq(opp);
+                new_oppinfo.volt = opp_get_voltage(opp);
+                rcu_read_unlock();
 
-                err = exynos4_bus_setvolt(data, opp, data->curr_opp);
+                err = exynos4_bus_setvolt(data, &new_oppinfo,
+                                          &data->curr_oppinfo);
                 if (err)
                         goto unlock;
 
                 switch (data->type) {
                 case TYPE_BUSF_EXYNOS4210:
-                        err = exynos4210_set_busclk(data, opp);
+                        err = exynos4210_set_busclk(data, &new_oppinfo);
                         break;
                 case TYPE_BUSF_EXYNOS4x12:
-                        err = exynos4x12_set_busclk(data, opp);
+                        err = exynos4x12_set_busclk(data, &new_oppinfo);
                         break;
                 default:
                         err = -EINVAL;
@@ -962,7 +998,7 @@ static int exynos4_busfreq_pm_notifier_event(struct notifier_block *this,
                 if (err)
                         goto unlock;
 
-                data->curr_opp = opp;
+                data->curr_oppinfo = new_oppinfo;
 unlock:
                 mutex_unlock(&data->lock);
                 if (err)
@@ -1027,13 +1063,17 @@ static int exynos4_busfreq_probe(struct platform_device *pdev)
                 }
         }
 
+        rcu_read_lock();
         opp = opp_find_freq_floor(dev, &exynos4_devfreq_profile.initial_freq);
         if (IS_ERR(opp)) {
+                rcu_read_unlock();
                 dev_err(dev, "Invalid initial frequency %lu kHz.\n",
                         exynos4_devfreq_profile.initial_freq);
                 return PTR_ERR(opp);
         }
-        data->curr_opp = opp;
+        data->curr_oppinfo.rate = opp_get_freq(opp);
+        data->curr_oppinfo.volt = opp_get_voltage(opp);
+        rcu_read_unlock();
 
         platform_set_drvdata(pdev, data);