On Tue, 15 Dec 2020 at 09:23, Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
>
> 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);
Reviewing this I noticed that in pwm_fan_resume() we use
DIV_ROUND_UP_ULL for what looks like essentially the same calculation.
Could we just switch this line to DIV_ROUND_UP_ULL instead?
>
> 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@xxxxxxxxxxxxxx>
> ---
> drivers/hwmon/pwm-fan.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index 1f63807c0399..ec171f2b684a 100644
> --- a/drivers/hwmon/pwm-fan.c
> +++ b/drivers/hwmon/pwm-fan.c
> @@ -324,8 +324,18 @@ 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;
>
>
> base-commit: 2c85ebc57b3e1817b6ce1a6b703928e113a90442
> --
> 2.29.2
>
--
Paul Barker
Konsulko Group
