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iio: adc: hx711: fix bug in sampling of data

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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: c3b2fdd0ea ("iio: adc: hx711: Add IIO driver for AVIA HX711")
Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
Andreas Klinger 2019-09-09 14:37:21 +02:00 committed by Jonathan Cameron
parent 6c59a962e0
commit 4043ecfb5f
1 changed files with 5 additions and 5 deletions
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10
drivers/iio/adc/hx711.c
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@ -100,14 +100,14 @@ 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 +117,6 @@ 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 +124,7 @@ 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 +132,8 @@ 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)