[CPUFREQ] ondemand/conservative: sanitize sampling_rate restrictions

Limit sampling rate to transition_latency * 100 or kernel limits.
If sampling_rate is tried to be set too low, set the lowest allowed value.

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Dave Jones <davej@redhat.com>

1 files changed, 18 insertions, 10 deletions

diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index 0912d7ca8cd7..8d541c69aec6 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -54,8 +54,20 @@ static unsigned int def_sampling_rate;
                         (MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10))
 #define MIN_SAMPLING_RATE                       \
                         (def_sampling_rate / MIN_SAMPLING_RATE_RATIO)
+/* Above MIN_SAMPLING_RATE will vanish with its sysfs file soon
+ * Define the minimal settable sampling rate to the greater of:
+ *   - "HW transition latency" * 100 (same as default sampling / 10)
+ *   - MIN_STAT_SAMPLING_RATE
+ * To avoid that userspace shoots itself.
+*/
+static unsigned int minimum_sampling_rate(void)
+{
+        return max(def_sampling_rate / 10, MIN_STAT_SAMPLING_RATE);
+}
+
+/* This will also vanish soon with removing sampling_rate_max */
 #define MAX_SAMPLING_RATE                       (500 * def_sampling_rate)
-#define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER    (1000)
+#define LATENCY_MULTIPLIER                      (1000)
 #define DEF_SAMPLING_DOWN_FACTOR                (1)
 #define MAX_SAMPLING_DOWN_FACTOR                (10)
 #define TRANSITION_LATENCY_LIMIT                (10 * 1000 * 1000)
@@ -208,13 +220,11 @@ static ssize_t store_sampling_rate(struct cpufreq_policy *unused,
         ret = sscanf(buf, "%u", &input);
 
         mutex_lock(&dbs_mutex);
-        if (ret != 1 || input > MAX_SAMPLING_RATE ||
-            input < MIN_SAMPLING_RATE) {
+        if (ret != 1) {
                 mutex_unlock(&dbs_mutex);
                 return -EINVAL;
         }
-
-        dbs_tuners_ins.sampling_rate = input;
+        dbs_tuners_ins.sampling_rate = max(input, minimum_sampling_rate());
         mutex_unlock(&dbs_mutex);
 
         return count;
@@ -540,11 +550,9 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                         if (latency == 0)
                                 latency = 1;
 
-                        def_sampling_rate = 10 * latency *
-                                        DEF_SAMPLING_RATE_LATENCY_MULTIPLIER;
-
-                        if (def_sampling_rate < MIN_STAT_SAMPLING_RATE)
-                                def_sampling_rate = MIN_STAT_SAMPLING_RATE;
+                        def_sampling_rate =
+                                max(10 * latency * LATENCY_MULTIPLIER,
+                                    MIN_STAT_SAMPLING_RATE);
 
                         dbs_tuners_ins.sampling_rate = def_sampling_rate;