From: Paul Barker pbarker@konsulko.com
[ Upstream commit fd8feec665fef840277515a5c2b9b7c3e3970fad ]
To convert the number of pulses counted into an RPM estimation, we need to divide by the width of our measurement interval instead of multiplying by it. If the width of the measurement interval is zero we don't update the RPM value to avoid dividing by zero.
We also don't need to do 64-bit division, with 32-bits we can handle a fan running at over 4 million RPM.
Signed-off-by: Paul Barker pbarker@konsulko.com Link: https://lore.kernel.org/r/20201111164643.7087-1-pbarker@konsulko.com Signed-off-by: Guenter Roeck linux@roeck-us.net Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/hwmon/pwm-fan.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c index 17bb64299bfd8..3642086498d98 100644 --- a/drivers/hwmon/pwm-fan.c +++ b/drivers/hwmon/pwm-fan.c @@ -54,16 +54,18 @@ static irqreturn_t pulse_handler(int irq, void *dev_id) static void sample_timer(struct timer_list *t) { struct pwm_fan_ctx *ctx = from_timer(ctx, t, rpm_timer); + unsigned int delta = ktime_ms_delta(ktime_get(), ctx->sample_start); int pulses; - u64 tmp;
- pulses = atomic_read(&ctx->pulses); - atomic_sub(pulses, &ctx->pulses); - tmp = (u64)pulses * ktime_ms_delta(ktime_get(), ctx->sample_start) * 60; - do_div(tmp, ctx->pulses_per_revolution * 1000); - ctx->rpm = tmp; + if (delta) { + pulses = atomic_read(&ctx->pulses); + atomic_sub(pulses, &ctx->pulses); + ctx->rpm = (unsigned int)(pulses * 1000 * 60) / + (ctx->pulses_per_revolution * delta); + + ctx->sample_start = ktime_get(); + }
- ctx->sample_start = ktime_get(); mod_timer(&ctx->rpm_timer, jiffies + HZ); }