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SubjectRe: [PATCH v2 1/3] iio: adc: hx711: fix bug in sampling of data
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,

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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