The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4043ecfb5fc4355a090111e14faf7945ff0fdbd5 Mon Sep 17 00:00:00 2001

From: Andreas Klinger ak@it-klinger.de Date: Mon, 9 Sep 2019 14:37:21 +0200 Subject: [PATCH] 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.

Fixes: c3b2fdd0ea7e ("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

diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c index 88c7fe15003b..62e6c8badd22 100644 --- a/drivers/iio/adc/hx711.c +++ b/drivers/iio/adc/hx711.c @@ -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)