hwmon: (pwm-fan) Ensure that calculation doesn't discard big period values
[ Upstream commit 1eda52334e
]
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
5.4-rM2-2.2.x-imx-squashed
parent
1229d43396
commit
1d05b91ab7
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@ -330,8 +330,18 @@ static int pwm_fan_probe(struct platform_device *pdev)
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ctx->pwm_value = MAX_PWM;
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/* Set duty cycle to maximum allowed and enable PWM output */
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pwm_init_state(ctx->pwm, &state);
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/*
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* __set_pwm assumes that MAX_PWM * (period - 1) fits into an unsigned
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* long. Check this here to prevent the fan running at a too low
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* frequency.
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*/
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if (state.period > ULONG_MAX / MAX_PWM + 1) {
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dev_err(dev, "Configured period too big\n");
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return -EINVAL;
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}
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/* Set duty cycle to maximum allowed and enable PWM output */
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state.duty_cycle = ctx->pwm->args.period - 1;
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state.enabled = true;
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