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

Rafael J. Wysocki
2012-10-25T23:52:48Z

On Thursday, October 25, 2012 06:32:43 PM Nishanth Menon wrote:
> 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");

Care to avoid printing the tailing space?

Rafael

> +
> + 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),
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.