pwm: Clarify which state pwm_get_state() returns

Given that lowlevel drivers usually cannot implement exactly what a
consumer requests with pwm_apply_state() there is some rounding
involved.

pwm_get_state() returns the setting that was requested most recently by
the consumer (opposed to what was actually implemented in hardware in
reply to the last request). Clarify this in the function kerneldoc.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

diff --git a/Documentation/driver-api/pwm.rst b/Documentation/driver-api/pwm.rst
index ab62f1b..381f3c4 100644 (file)
--- a/Documentation/driver-api/pwm.rst
+++ b/Documentation/driver-api/pwm.rst
@@ -55,7 +55,11 @@ several parameter at once. For example, if you see pwm_config() and
 pwm_{enable,disable}() calls in the same function, this probably means you
 should switch to pwm_apply_state().
 
-The PWM user API also allows one to query the PWM state with pwm_get_state().
+The PWM user API also allows one to query the last applied PWM state with
+pwm_get_last_applied_state(). Note this is different to what the driver has
+actually implemented if the request cannot be implemented exactly with the
+hardware in use. There is currently no way for consumers to get the actually
+implemented settings.
 
 In addition to the PWM state, the PWM API also exposes PWM arguments, which
 are the reference PWM config one should use on this PWM.

diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 8f4eefd..5bb90af 100644 (file)
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -91,6 +91,11 @@ struct pwm_device {
  * pwm_get_state() - retrieve the current PWM state
  * @pwm: PWM device
  * @state: state to fill with the current PWM state
+ *
+ * The returned PWM state represents the state that was applied by a previous call to
+ * pwm_apply_state(). Drivers may have to slightly tweak that state before programming it to
+ * hardware. If pwm_apply_state() was never called, this returns either the current hardware
+ * state (if supported) or the default settings.
  */
 static inline void pwm_get_state(const struct pwm_device *pwm,
                                 struct pwm_state *state)