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>

diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
index 91cf90bd4083205b17a9e9bfc19f01172be94646..6017e311a87912e98efcf0abf531610f0c9d1b0c 100644 (file)
--- a/drivers/pwm/pwm-sifive.c
+++ b/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;
 }