pwm: sysfs: Add PWM capture support

Allow a user to read PWM capture results from sysfs. To start a capture
and read the result, simply read the file:

  $ cat $PWMCHIP/capture

The output format is "<period> <duty cycle>".

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

2 files changed, 26 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-pwm b/Documentation/ABI/testing/sysfs-class-pwm
index c479d77b67c5..c20e61354561 100644
--- a/Documentation/ABI/testing/sysfs-class-pwm
+++ b/Documentation/ABI/testing/sysfs-class-pwm
@@ -77,3 +77,12 @@ Description:
                 Enable/disable the PWM signal.
                 0 is disabled
                 1 is enabled
+
+What:           /sys/class/pwm/pwmchipN/pwmX/capture
+Date:           June 2016
+KernelVersion:  4.8
+Contact:        Lee Jones <lee.jones@linaro.org>
+Description:
+                Capture information about a PWM signal. The output format is a
+                pair unsigned integers (period and duty cycle), separated by a
+                single space.
diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c
index d98599249a05..c3b1b563480e 100644
--- a/drivers/pwm/sysfs.c
+++ b/drivers/pwm/sysfs.c
@@ -208,16 +208,33 @@ static ssize_t polarity_store(struct device *child,
         return ret ? : size;
 }
 
+static ssize_t capture_show(struct device *child,
+                            struct device_attribute *attr,
+                            char *buf)
+{
+        struct pwm_device *pwm = child_to_pwm_device(child);
+        struct pwm_capture result;
+        int ret;
+
+        ret = pwm_capture(pwm, &result, jiffies_to_msecs(HZ));
+        if (ret)
+                return ret;
+
+        return sprintf(buf, "%u %u\n", result.period, result.duty_cycle);
+}
+
 static DEVICE_ATTR_RW(period);
 static DEVICE_ATTR_RW(duty_cycle);
 static DEVICE_ATTR_RW(enable);
 static DEVICE_ATTR_RW(polarity);
+static DEVICE_ATTR_RO(capture);
 
 static struct attribute *pwm_attrs[] = {
         &dev_attr_period.attr,
         &dev_attr_duty_cycle.attr,
         &dev_attr_enable.attr,
         &dev_attr_polarity.attr,
+        &dev_attr_capture.attr,
         NULL
 };
 ATTRIBUTE_GROUPS(pwm);