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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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