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
bail out instead of dividing by it.
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@xxxxxxxxxxxx>
---
drivers/hwmon/pwm-fan.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
index edc0453be25a..24cfed4d625e 100644
--- a/drivers/hwmon/pwm-fan.c
+++ b/drivers/hwmon/pwm-fan.c
@@ -55,14 +55,19 @@ 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);
+ } else {
+ dev_err(ctx->dev,
+ "Cannot determine fan RPM as time delta is zero\n");
+ ctx->rpm = 0;
+ }
ctx->sample_start = ktime_get();
mod_timer(&ctx->rpm_timer, jiffies + HZ);
--
2.29.2
