FAILED: patch "[PATCH] iio: adc: hx711: fix bug in sampling of data" failed to apply to 4.14-stable tree

PATCH [email protected] 2 participants 2 messages Oct 14, 2019 – Oct 15, 2019

Subsystems (3)

Stable branch IIO Avia HX711 Analog digital converter IIO driver

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[email protected]

author maintainer

2019-10-14 15:01 UTC #0 lore raw

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 <[email protected]>.

thanks,

greg k-h

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

From 4043ecfb5fc4355a090111e14faf7945ff0fdbd5 Mon Sep 17 00:00:00 2001
From: Andreas Klinger <[email protected]>
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 <[email protected]>

Cc <[email protected]>

Signed-off-by Jonathan Cameron <[email protected]>

drivers/iio/adc/hx711.c +5 -5

index 88c7fe15003b..62e6c8badd22 100644
@@ -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)

Sasha Levin

maintainer

2019-10-15 00:57 UTC #1 lore raw

Quoted 24 lines · On Mon, Oct 14, 2019 at 05:01:26PM +0200, [email protected] wrote:

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 <[email protected]>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 4043ecfb5fc4355a090111e14faf7945ff0fdbd5 Mon Sep 17 00:00:00 2001
From: Andreas Klinger <[email protected]>
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.

Quoted 7 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]>
Cc <[email protected]>
Signed-off-by Jonathan Cameron <[email protected]>

I've queued up this patch in addition: 461631face580 ("iio: hx711: add delay until DOUT is ready") and queued both for 4.14. It's not needed on older kernels.

Signature · 2 lines

Thanks,
Sasha