Jonathan Cameron writes:
> On 27/01/16 22:46, Abhilash Jindal wrote:
> > Wall time obtained from ktime_get_real_ns is susceptible to sudden jumps due to
> > user setting the time or due to NTP. Boot time is constantly increasing time
> > better suited for comparing two timestamps.
> >
> > Signed-off-by: Abhilash Jindal <klock.android@xxxxxxxxx>
> Seems sensible to me, but would like Richard / Harald to take a quick
> look before I apply it.
Reviewed-by: Harald Geyer <harald@xxxxxxxxx>
I can't test this right now, but I think it will fix an odd issue I
have seen in a log file (apparently was completely off track debugging it).
As this very likely is a real world issue, I'd recommend applying the patch
to the fixes branch, so that it hopefully gets picked up for LTS kernels.
I used ktime_get_real_ns() because that is what iio_get_time_ns() uses.
I should have thought about this twice - sorry about being sloppy!
I just grepped the other iio drivers and none is using iio_get_time_ns() in
a comparision like dht11 did, so maybe the other uses are safe. However
I couldn't check variables containing timestamps that way, so maybe
reviewing the users of iio_get_time_ns(), whether wall time is actually
what is wanted, would be a worthwhile task if somebody has the time ...
Thanks for the patch!
Harald
> Thanks,
>
> Jonathan
> > ---
> > drivers/iio/humidity/dht11.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/iio/humidity/dht11.c b/drivers/iio/humidity/dht11.c
> > index 1165b1c..cfc5a05 100644
> > --- a/drivers/iio/humidity/dht11.c
> > +++ b/drivers/iio/humidity/dht11.c
> > @@ -117,7 +117,7 @@ static int dht11_decode(struct dht11 *dht11, int offset, int timeres)
> > if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
> > return -EIO;
> >
> > - dht11->timestamp = ktime_get_real_ns();
> > + dht11->timestamp = ktime_get_boot_ns();
> > if (hum_int < 20) { /* DHT22 */
> > dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
> > ((temp_int & 0x80) ? -100 : 100);
> > @@ -145,7 +145,7 @@ static irqreturn_t dht11_handle_irq(int irq, void *data)
> >
> > /* TODO: Consider making the handler safe for IRQ sharing */
> > if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
> > - dht11->edges[dht11->num_edges].ts = ktime_get_real_ns();
> > + dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
> > dht11->edges[dht11->num_edges++].value =
> > gpio_get_value(dht11->gpio);
> >
> > @@ -164,7 +164,7 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
> > int ret, timeres;
> >
> > mutex_lock(&dht11->lock);
> > - if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_real_ns()) {
> > + if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
> > timeres = ktime_get_resolution_ns();
> > if (DHT11_DATA_BIT_HIGH < 2 * timeres) {
> > dev_err(dht11->dev, "timeresolution %dns too low\n",
> > @@ -279,7 +279,7 @@ static int dht11_probe(struct platform_device *pdev)
> > return -EINVAL;
> > }
> >
> > - dht11->timestamp = ktime_get_real_ns() - DHT11_DATA_VALID_TIME - 1;
> > + dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
> > dht11->num_edges = -1;
> >
> > platform_set_drvdata(pdev, iio);
> >
>
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