linux-kernel - [PATCH] pwm: fix undefined behavior in stm32_pwm

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Date:   Wed, 25 Jan 2017 23:31:34 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Lee Jones <lee.jones@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        linux-pwm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] pwm: fix undefined behavior in stm32_pwm_apply

The stm32_pwm_apply randomly sets the polarity or doesn't,
as pointed out by this gcc warning:

drivers/pwm/pwm-stm32.c: In function 'stm32_pwm_apply':
drivers/pwm/pwm-stm32.c:204:33: error: 'curstate.polarity' may be used uninitialized in this function [-Werror=maybe-uninitialized]

I assume it was meant to compare the new state to the current
state rather than an uninitialized stack variable, so let's
do that instead.

Fixes: bafffb6e7bd1 ("pwm: Add driver for STM32 plaftorm")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/pwm/pwm-stm32.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c
index ce6232ebefe1..6139512aab7b 100644
--- a/drivers/pwm/pwm-stm32.c
+++ b/drivers/pwm/pwm-stm32.c
@@ -189,7 +189,6 @@ static void stm32_pwm_disable(struct stm32_pwm *priv, int ch)
 static int stm32_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			   struct pwm_state *state)
 {
-	struct pwm_state curstate;
 	bool enabled;
 	struct stm32_pwm *priv = to_stm32_pwm_dev(chip);
 	int ret;
@@ -201,7 +200,7 @@ static int stm32_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 		return 0;
 	}
 
-	if (state->polarity != curstate.polarity)
+	if (state->polarity != pwm->state.polarity)
 		stm32_pwm_set_polarity(priv, pwm->hwpwm, state->polarity);
 
 	ret = stm32_pwm_config(priv, pwm->hwpwm,
-- 
2.9.0