Re: [PATCH 1/2] pwm: atmel-tcb: Fix race condition and convert to guards
From: Nicolas Ferre <nicolas.ferre@microchip.com>
Date: 2024-07-10 14:17:58
Also in:
linux-pwm
On 09/07/2024 at 12:18, Uwe Kleine-König wrote:
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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 <redacted>Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com> And I like the conversion to the "guard" lock helper. Best regards, Nicolas
quoted hunk ↗ jump to hunk
--- drivers/pwm/pwm-atmel-tcb.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)diff --git a/drivers/pwm/pwm-atmel-tcb.c b/drivers/pwm/pwm-atmel-tcb.c index 528e54c5999d..aca11493239a 100644 --- 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;base-commit: 120a528213b6693214e3cbc24a9c3052a4b1024b -- 2.43.0