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: 9421bade0765 ("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.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

diff --git a/drivers/pwm/pwm-atmel-tcb.c b/drivers/pwm/pwm-atmel-tcb.c
index 528e54c5999d85957feddbf8effcbc17e83a0cda..aca11493239a59d336164b0fe80c31b78ae6229c 100644 (file)
--- a/drivers/pwm/pwm-atmel-tcb.c
+++ b/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;