PM / devfreq: Add sysfs node to expose available frequencies

devfreq governors such as ondemand are controlled by a min and
max frequency, while governors like userspace governor allow us
to set a specific frequency.
However, for the same specific device, depending on the SoC, the
available frequencies can vary.

So expose the available frequencies as a snapshot over sysfs to
allow informed decisions.

This was inspired by cpufreq framework's equivalent for similar
usage sysfs node: scaling_available_frequencies.

Cc: Rajagopal Venkat <rajagopal.venkat@linaro.org>
Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Kevin Hilman <khilman@ti.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 789af4ff5c9c..c44e562bdfe0 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -570,9 +570,41 @@ static ssize_t show_max_freq(struct device *dev, struct device_attribute *attr,
         return sprintf(buf, "%lu\n", to_devfreq(dev)->max_freq);
 }
 
+static ssize_t show_available_freqs(struct device *d,
+                                    struct device_attribute *attr,
+                                    char *buf)
+{
+        struct devfreq *df = to_devfreq(d);
+        struct device *dev = df->dev.parent;
+        struct opp *opp;
+        ssize_t count = 0;
+        unsigned long freq = 0;
+
+        rcu_read_lock();
+        do {
+                opp = opp_find_freq_ceil(dev, &freq);
+                if (IS_ERR(opp))
+                        break;
+
+                count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
+                                   "%lu ", freq);
+                freq++;
+        } while (1);
+        rcu_read_unlock();
+
+        /* Truncate the trailing space */
+        if (count)
+                count--;
+
+        count += sprintf(&buf[count], "\n");
+
+        return count;
+}
+
 static struct device_attribute devfreq_attrs[] = {
         __ATTR(governor, S_IRUGO, show_governor, NULL),
         __ATTR(cur_freq, S_IRUGO, show_freq, NULL),
+        __ATTR(available_frequencies, S_IRUGO, show_available_freqs, NULL),
         __ATTR(target_freq, S_IRUGO, show_target_freq, NULL),
         __ATTR(polling_interval, S_IRUGO | S_IWUSR, show_polling_interval,
                store_polling_interval),