pwm: sifive: Reduce time the controller lock is held

The lock is only to serialize access and update to user_count and
approx_period between different PWMs served by the same pwm_chip.
So the lock needs only to be taken during the check if the (chip global)
period can and/or needs to be changed.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-sifive.c

@@ -41,7 +41,7 @@
 
 struct pwm_sifive_ddata {
 	struct pwm_chip	chip;
-	struct mutex lock; /* lock to protect user_count */
+	struct mutex lock; /* lock to protect user_count and approx_period */
 	struct notifier_block notifier;
 	struct clk *clk;
 	void __iomem *regs;
@@ -76,6 +76,7 @@ static void pwm_sifive_free(struct pwm_chip *chip, struct pwm_device *pwm)
 	mutex_unlock(&ddata->lock);
 }
 
+/* Called holding ddata->lock */
 static void pwm_sifive_update_clock(struct pwm_sifive_ddata *ddata,
 				    unsigned long rate)
 {
@@ -144,7 +145,6 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 		return ret;
 	}
 
-	mutex_lock(&ddata->lock);
 	cur_state = pwm->state;
 	enabled = cur_state.enabled;
 
@@ -163,14 +163,17 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	/* The hardware cannot generate a 100% duty cycle */
 	frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
 
+	mutex_lock(&ddata->lock);
 	if (state->period != ddata->approx_period) {
 		if (ddata->user_count != 1) {
+			mutex_unlock(&ddata->lock);
 			ret = -EBUSY;
 			goto exit;
 		}
 		ddata->approx_period = state->period;
 		pwm_sifive_update_clock(ddata, clk_get_rate(ddata->clk));
 	}
+	mutex_unlock(&ddata->lock);
 
 	writel(frac, ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
 
@@ -185,7 +188,6 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 
 exit:
 	clk_disable(ddata->clk);
-	mutex_unlock(&ddata->lock);
 	return ret;
 }