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hwmon: (pwm-fan) Ensure that calculation doesn't discard big period values

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With MAX_PWM being defined to 255 the code

	unsigned long period;
	...
	period = ctx->pwm->args.period;
	state.duty_cycle = DIV_ROUND_UP(pwm * (period - 1), MAX_PWM);

calculates a too small value for duty_cycle if the configured period is
big (either by discarding the 64 bit value ctx->pwm->args.period or by
overflowing the multiplication). As this results in a too slow fan and
so maybe an overheating machine better be safe than sorry and error out
in .probe.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20201215092031.152243-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Uwe Kleine-König 2020-12-15 10:20:30 +01:00 committed by Guenter Roeck
parent e042f151ec
commit 1eda52334e
1 changed files with 11 additions and 1 deletions
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12
drivers/hwmon/pwm-fan.c
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@ -334,8 +334,18 @@ static int pwm_fan_probe(struct platform_device *pdev)
ctx->pwm_value = MAX_PWM;
/* Set duty cycle to maximum allowed and enable PWM output */
pwm_init_state(ctx->pwm, &state);
/*
* __set_pwm assumes that MAX_PWM * (period - 1) fits into an unsigned
* long. Check this here to prevent the fan running at a too low
* frequency.
*/
if (state.period > ULONG_MAX / MAX_PWM + 1) {
dev_err(dev, "Configured period too big\n");
return -EINVAL;
}
/* Set duty cycle to maximum allowed and enable PWM output */
state.duty_cycle = ctx->pwm->args.period - 1;
state.enabled = true;