max is the maximum number of nanoseconds accepted as duty or period by a
certain device. resolution is the minimum step actually handled by the
hardware output.
This couple of attributes permit users:
1) to know the capabilities of the pwm output;
2) to set a really supported value (by using of resolution, a precise
computation is possible);
3) to avoid them setting invalid (too big) periods.
A default value of resolution=1 and max=MAX_INT is provided in this
patch, but driver maintainers are encouraged to properly fill the new
fields in struct pwm_device.
Signed-off-by: Aurelio Colosimo <aure...@aureliocolosimo.it>
---
Documentation/pwm.txt | 7 +++++++
drivers/pwm/core.c | 2 ++
drivers/pwm/sysfs.c | 22 ++++++++++++++++++++++
include/linux/pwm.h | 2 ++
4 files changed, 33 insertions(+)
diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
index ca895fd..dbb1a16 100644
--- a/Documentation/pwm.txt
+++ b/Documentation/pwm.txt
@@ -74,6 +74,13 @@ period - The total period of the PWM signal (read/write).
duty_cycle - The active time of the PWM signal (read/write).
Value is in nanoseconds and must be less than the period.
+resolution - The resolution of duty_cycle and period.
+ Value is in nanoseconds and is the min step period and duty can
+ change.
+
+max - The max value for period.
+ Value is in nanoseconds.
+
polarity - Changes the polarity of the PWM signal (read/write).
Writes to this property only work if the PWM chip supports changing
the polarity. The polarity can only be changed if the PWM is not
diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 4b66bf0..d973ed7 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -259,6 +259,8 @@ int pwmchip_add(struct pwm_chip *chip)
pwm->chip = chip;
pwm->pwm = chip->base + i;
pwm->hwpwm = i;
+ pwm->resolution = 1;
+ pwm->max = UINT_MAX;
radix_tree_insert(&pwm_tree, pwm->pwm, pwm);
}
diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c
index c1d6064..1bb77e2 100644
--- a/drivers/pwm/sysfs.c
+++ b/drivers/pwm/sysfs.c
@@ -157,16 +157,38 @@ static ssize_t pwm_polarity_store(struct device *child,
return ret ? : size;
}
+static ssize_t pwm_resolution_show(struct device *child,
+ struct device_attribute *attr,
+ char *buf)
+{
+ const struct pwm_device *pwm = child_to_pwm_device(child);
+
+ return sprintf(buf, "%u\n", pwm->resolution);
+}
+
+static ssize_t pwm_max_show(struct device *child,
+ struct device_attribute *attr,
+ char *buf)
+{
+ const struct pwm_device *pwm = child_to_pwm_device(child);
+
+ return sprintf(buf, "%u\n", pwm->max);
+}
+
static DEVICE_ATTR(period, 0644, pwm_period_show, pwm_period_store);
static DEVICE_ATTR(duty_cycle, 0644, pwm_duty_cycle_show,
pwm_duty_cycle_store);
static DEVICE_ATTR(enable, 0644, pwm_enable_show, pwm_enable_store);
static DEVICE_ATTR(polarity, 0644, pwm_polarity_show, pwm_polarity_store);
+static DEVICE_ATTR(resolution, 0444, pwm_resolution_show, NULL);
+static DEVICE_ATTR(max, 0444, pwm_max_show, NULL);
static struct attribute *pwm_attrs[] = {
&dev_attr_period.attr,
&dev_attr_duty_cycle.attr,
&dev_attr_enable.attr,
&dev_attr_polarity.attr,
+ &dev_attr_resolution.attr,
+ &dev_attr_max.attr,
NULL
};
ATTRIBUTE_GROUPS(pwm);
diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 9bacf35..c4cc794 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -90,6 +90,8 @@ struct pwm_device {
unsigned int period; /* in nanoseconds */
unsigned int duty_cycle; /* in nanoseconds */
+ unsigned int resolution; /* in nanoseconds */
+ unsigned int max; /* in nanoseconds */
enum pwm_polarity polarity;
};
--
1.9.1
--
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