[for-next PATCH] PM / devfreq: Add sysfs node to expose available frequencies

Nishanth Menon
2012-10-25T23:32:57Z

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>
---
Applies on top of Rafael's linux-next branch:
git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git
linux-next b960e9a Merge branch 'pm-sleep-next' into linux-next

Example output from Beagleboard XM (3730) using a dummy test driver
http://pastebin.pandaboard.org/index.php/view/85100576 :

/sys/devices/platform/iva.0/devfreq/iva.0 # cat available_frequencies
260000000 520000000 660000000

Documentation/ABI/testing/sysfs-class-devfreq | 9 +++++++++
drivers/devfreq/devfreq.c | 26 +++++++++++++++++++++++++
2 files changed, 35 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
index e6cf08e..e672ccb 100644
--- a/Documentation/ABI/testing/sysfs-class-devfreq
+++ b/Documentation/ABI/testing/sysfs-class-devfreq
@@ -51,3 +51,12 @@ Description:
The /sys/class/devfreq/.../userspace/set_freq shows and
sets the requested frequency for the devfreq object if
userspace governor is in effect.
+
+What: /sys/class/devfreq/.../available_frequencies
+Date: October 2012
+Contact: Nishanth Menon <nm@ti.com>
+Description:
+ The /sys/class/devfreq/.../available_frequencies shows
+ the available frequencies of the corresponding devfreq object.
+ This is a snapshot of available frequencies and not limited
+ by the min/max frequency restrictions.
diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index d02ee7e..2f6ad6b 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -571,9 +571,35 @@ 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 += sprintf(&buf[count], "%lu ", freq);
+ freq++;
+ } while (1);
+ rcu_read_unlock();
+ 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),
--
1.7.9.5