linux-kernel - [PATCH] pwm: don't allow duty cycle higher than period

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Message-Id: <1464296730-121773-1-git-send-email-briannorris@chromium.org>
Date:	Thu, 26 May 2016 14:05:30 -0700
From:	Brian Norris <briannorris@...omium.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	linux-pwm@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	Brian Norris <computersforpeace@...il.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Doug Anderson <dianders@...omium.org>,
	Brian Norris <briannorris@...omium.org>
Subject: [PATCH] pwm: don't allow duty cycle higher than period

It doesn't make sense to allow the duty cycle to be larger than the
period. I can see this behavior by, e.g.:

  # echo 1 > /sys/class/pwm/pwmchip0/export
  # cat /sys/class/pwm/pwmchip0/pwm1/period
  100
  # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle
  [... driver may or may not reject the value, or trigger some logic bug ...]

It's better to see:

  # echo 1 > /sys/class/pwm/pwmchip0/export
  # cat /sys/class/pwm/pwmchip0/pwm1/period
  100
  # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle
  -bash: echo: write error: Invalid argument

Signed-off-by: Brian Norris <briannorris@...omium.org>
---
 drivers/pwm/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index dba3843c53b8..9246b60f894a 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -463,6 +463,9 @@ int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state)
 	if (!memcmp(state, &pwm->state, sizeof(*state)))
 		return 0;
 
+	if (state->duty_cycle > state->period)
+		return -EINVAL;
+
 	if (pwm->chip->ops->apply) {
 		err = pwm->chip->ops->apply(pwm->chip, pwm, state);
 		if (err)
-- 
2.8.0.rc3.226.g39d4020