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SubjectRe: [PATCH v2 1/3] iio: adc: hx711: fix bug in sampling of data
On Sun, 15 Sep 2019 13:53:26 +0100
Jonathan Cameron <jic23@kernel.org> wrote:

> On Mon, 9 Sep 2019 14:37:21 +0200
> Andreas Klinger <ak@it-klinger.de> wrote:
>
> > Fix bug in sampling function hx711_cycle() when interrupt occures while
> > PD_SCK is high. If PD_SCK is high for at least 60 us power down mode of
> > the sensor is entered which in turn leads to a wrong measurement.
> >
> > Switch off interrupts during a PD_SCK high period and move query of DOUT
> > to the latest point of time which is at the end of PD_SCK low period.
> >
> > This bug exists in the driver since it's initial addition. The more
> > interrupts on the system the higher is the probability that it happens.
> >
> > Fixes: c3b2fdd0ea7e ("iio: adc: hx711: Add IIO driver for AVIA HX711")
> >
> > Signed-off-by: Andreas Klinger <ak@it-klinger.de>
>
> Applied to the fixes-togreg branch of iio.git and marked for stable.
>
> Thanks,
I should have waited for my local tests to finish. This result in
val being unused, so I've removed it.

Thanks,

Jonathan

>
> Jonathan
>
> > ---
> > drivers/iio/adc/hx711.c | 9 +++++----
> > 1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c
> > index 88c7fe15003b..0678964dbd21 100644
> > --- a/drivers/iio/adc/hx711.c
> > +++ b/drivers/iio/adc/hx711.c
> > @@ -101,13 +101,14 @@ struct hx711_data {
> > static int hx711_cycle(struct hx711_data *hx711_data)
> > {
> > int val;
> > + unsigned long flags;
> >
> > /*
> > * if preempted for more then 60us while PD_SCK is high:
> > * hx711 is going in reset
> > * ==> measuring is false
> > */
> > - preempt_disable();
> > + local_irq_save(flags);
> > gpiod_set_value(hx711_data->gpiod_pd_sck, 1);
> >
> > /*
> > @@ -117,7 +118,6 @@ static int hx711_cycle(struct hx711_data *hx711_data)
> > */
> > ndelay(hx711_data->data_ready_delay_ns);
> >
> > - val = gpiod_get_value(hx711_data->gpiod_dout);
> > /*
> > * here we are not waiting for 0.2 us as suggested by the datasheet,
> > * because the oscilloscope showed in a test scenario
> > @@ -125,7 +125,7 @@ static int hx711_cycle(struct hx711_data *hx711_data)
> > * and 0.56 us for PD_SCK low on TI Sitara with 800 MHz
> > */
> > gpiod_set_value(hx711_data->gpiod_pd_sck, 0);
> > - preempt_enable();
> > + local_irq_restore(flags);
> >
> > /*
> > * make it a square wave for addressing cases with capacitance on
> > @@ -133,7 +133,8 @@ static int hx711_cycle(struct hx711_data *hx711_data)
> > */
> > ndelay(hx711_data->data_ready_delay_ns);
> >
> > - return val;
> > + /* sample as late as possible */
> > + return gpiod_get_value(hx711_data->gpiod_dout);
> > }
> >
> > static int hx711_read(struct hx711_data *hx711_data)
>

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