pwm: atmel-tcb: Fix race condition and convert to guards

The hardware only supports a single period length for both PWM outputs. So
atmel_tcb_pwm_config() checks the configuration of the other output if it's
compatible with the currently requested setting. The register values are
then actually updated in atmel_tcb_pwm_enable(). To make this race free
the lock must be held during the whole process, so grab the lock in
.apply() instead of individually in atmel_tcb_pwm_disable() and
atmel_tcb_pwm_enable() which then also covers atmel_tcb_pwm_config().

To simplify handling, use the guard helper to let the compiler care for
unlocking. Otherwise unlocking would be more difficult as there is more
than one exit path in atmel_tcb_pwm_apply().

Fixes: 9421bade ("pwm: atmel: add Timer Counter Block PWM driver")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20240709101806.52394-3-u.kleine-koenig@baylibre.comSigned-off-by: Uwe Kleine-König <ukleinek@kernel.org>

drivers/pwm/pwm-atmel-tcb.c

@@ -81,7 +81,8 @@ static int atmel_tcb_pwm_request(struct pwm_chip *chip,
 	tcbpwm->period = 0;
 	tcbpwm->div = 0;
 
-	spin_lock(&tcbpwmc->lock);
+	guard(spinlock)(&tcbpwmc->lock);
+
 	regmap_read(tcbpwmc->regmap, ATMEL_TC_REG(tcbpwmc->channel, CMR), &cmr);
 	/*
 	 * Get init config from Timer Counter registers if
@@ -107,7 +108,6 @@ static int atmel_tcb_pwm_request(struct pwm_chip *chip,
 
 	cmr |= ATMEL_TC_WAVE | ATMEL_TC_WAVESEL_UP_AUTO | ATMEL_TC_EEVT_XC0;
 	regmap_write(tcbpwmc->regmap, ATMEL_TC_REG(tcbpwmc->channel, CMR), cmr);
-	spin_unlock(&tcbpwmc->lock);
 
 	return 0;
 }
@@ -137,7 +137,6 @@ static void atmel_tcb_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm,
 	if (tcbpwm->duty == 0)
 		polarity = !polarity;
 
-	spin_lock(&tcbpwmc->lock);
 	regmap_read(tcbpwmc->regmap, ATMEL_TC_REG(tcbpwmc->channel, CMR), &cmr);
 
 	/* flush old setting and set the new one */
@@ -172,8 +171,6 @@ static void atmel_tcb_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm,
 			     ATMEL_TC_SWTRG);
 		tcbpwmc->bkup.enabled = 0;
 	}
-
-	spin_unlock(&tcbpwmc->lock);
 }
 
 static int atmel_tcb_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm,
@@ -194,7 +191,6 @@ static int atmel_tcb_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm,
 	if (tcbpwm->duty == 0)
 		polarity = !polarity;
 
-	spin_lock(&tcbpwmc->lock);
 	regmap_read(tcbpwmc->regmap, ATMEL_TC_REG(tcbpwmc->channel, CMR), &cmr);
 
 	/* flush old setting and set the new one */
@@ -256,7 +252,6 @@ static int atmel_tcb_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm,
 	regmap_write(tcbpwmc->regmap, ATMEL_TC_REG(tcbpwmc->channel, CCR),
 		     ATMEL_TC_SWTRG | ATMEL_TC_CLKEN);
 	tcbpwmc->bkup.enabled = 1;
-	spin_unlock(&tcbpwmc->lock);
 	return 0;
 }
 
@@ -341,9 +336,12 @@ static int atmel_tcb_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 static int atmel_tcb_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			       const struct pwm_state *state)
 {
+	struct atmel_tcb_pwm_chip *tcbpwmc = to_tcb_chip(chip);
 	int duty_cycle, period;
 	int ret;
 
+	guard(spinlock)(&tcbpwmc->lock);
+
 	if (!state->enabled) {
 		atmel_tcb_pwm_disable(chip, pwm, state->polarity);
 		return 0;