UPSTREAM: pwm: Add a helper to prepare a new PWM state

The pwm_init_state() helper prepares a new state object containing the
current PWM state except for the polarity and period fields which are
set to the reference values (those in struct pwm_args).

This is particularly useful for PWM users who want to apply a new duty-
cycle expressed relatively to the reference period without changing the
enable state.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
(cherry picked from commit a6a0dbbcfa469cf3e5c4d9522106c0b7b9e9e373)

Change-Id: Ib968e8fa6a49d5f853fc13cb4935e2af7494040f
Signed-off-by: David Wu <david.wu@rock-chips.com>

diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 59e5b19c05e54b85bcd4e529b1d167522c075d6d..510a7aad817006072037fbecd29ae062b226c4e9 100644 (file)
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -149,6 +149,39 @@ static inline void pwm_get_args(const struct pwm_device *pwm,
        *args = pwm->args;
 }
 
+/**
+ * pwm_init_state() - prepare a new state to be applied with pwm_apply_state()
+ * @pwm: PWM device
+ * @state: state to fill with the prepared PWM state
+ *
+ * This functions prepares a state that can later be tweaked and applied
+ * to the PWM device with pwm_apply_state(). This is a convenient function
+ * that first retrieves the current PWM state and the replaces the period
+ * and polarity fields with the reference values defined in pwm->args.
+ * Once the function returns, you can adjust the ->enabled and ->duty_cycle
+ * fields according to your needs before calling pwm_apply_state().
+ *
+ * ->duty_cycle is initially set to zero to avoid cases where the current
+ * ->duty_cycle value exceed the pwm_args->period one, which would trigger
+ * an error if the user calls pwm_apply_state() without adjusting ->duty_cycle
+ * first.
+ */
+static inline void pwm_init_state(const struct pwm_device *pwm,
+                                 struct pwm_state *state)
+{
+       struct pwm_args args;
+
+       /* First get the current state. */
+       pwm_get_state(pwm, state);
+
+       /* Then fill it with the reference config */
+       pwm_get_args(pwm, &args);
+
+       state->period = args.period;
+       state->polarity = args.polarity;
+       state->duty_cycle = 0;
+}
+
 /**
  * struct pwm_ops - PWM controller operations
  * @request: optional hook for requesting a PWM