iio: adc: hx711: fix bug in sampling of data
Subsystems (2)
Andreas Klinger
maintainerPATCH v2 1/3 iio: adc: hx711: fix bug in sampling of data
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.
--- drivers/iio/adc/hx711.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
drivers/iio/adc/hx711.c +5 -4
@@ -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)
Signature · 1 line
2.11.0
Quoted 7 lines · On Mon, 9 Sep 2019 14:37:21 +0200 Andreas Klinger <[email protected]> wrote:
Fix bug in sampling function
hx711_cycle()when interrupt occures whilePD_SCKis high. IfPD_SCKis 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_SCKhigh period and move query of DOUT to the latest point of time which is at the end ofPD_SCKlow period.
Quoted 6 lines
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 <[email protected]>
Applied to the fixes-togreg branch of iio.git and marked for stable.
Thanks,
Jonathan
Quoted 51 lines
--- drivers/iio/adc/hx711.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)drivers/iio/adc/hx711.c +5
-4@@ -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)
Quoted 13 lines · On Sun, 15 Sep 2019 13:53:26 +0100 Jonathan Cameron <[email protected]> wrote:
Quoted 10 lines · On Mon, 9 Sep 2019 14:37:21 +0200 Andreas Klinger <[email protected]> wrote:
Fix bug in sampling function
hx711_cycle()when interrupt occures whilePD_SCKis high. IfPD_SCKis 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_SCKhigh period and move query of DOUT to the latest point of time which is at the end ofPD_SCKlow 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.
Quoted 7 lines
Quoted 3 lines
Fixes c3b2fdd0ea7e ("iio: adc: hx711: Add IIO driver for AVIA HX711")Signed-off-by Andreas Klinger <[email protected]>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
Quoted 55 lines
Jonathan
Quoted 51 lines
--- drivers/iio/adc/hx711.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)drivers/iio/adc/hx711.c +5
-4@@ -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)