This is a note to let you know that I've just added the patch titled
hwmon: (pwm-fan) Fix RPM calculation
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
hwmon-pwm-fan-fix-rpm-calculation.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 6ddbe9e8ac5a10e748d48b81281a0a6d45ce2c9a
Author: Paul Barker <pbarker@xxxxxxxxxxxx>
Date: Wed Nov 11 16:46:43 2020 +0000
hwmon: (pwm-fan) Fix RPM calculation
[ 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@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20201111164643.7087-1-pbarker@xxxxxxxxxxxx
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
index 42ffd2e5182d5..c88ce77fe6763 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);
}
