linux-kernel - [PATCH v4 1/3] iio: hx711: add clock-frequency property in DT

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Date:   Wed, 4 Jul 2018 14:36:38 +0200
From:   Andreas Klinger <ak@...klinger.de>
To:     jic23@...nel.org, knaack.h@....de, lars@...afoo.de,
        pmeerw@...erw.net, robh+dt@...nel.org, mark.rutland@....com,
        mchehab@...nel.org, davem@...emloft.net,
        gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
        linus.walleij@...aro.org, rdunlap@...radead.org,
        devicetree@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 1/3] iio: hx711: add clock-frequency property in DT

Add clock-frequency property for hx711 ADC

This is the frequency of PD_SCK. It affects only the high value duration
since low value duration is not relevant and we are not able to switch
faster than the minimum duration specified.

After PD_SCK goes high DOUT is read just before PD_SCK goes down again.
This is necessary because of parasitic capacities on the wiring.

Signed-off-by: Andreas Klinger <ak@...klinger.de>
---
 Documentation/devicetree/bindings/iio/adc/avia-hx711.txt | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/adc/avia-hx711.txt b/Documentation/devicetree/bindings/iio/adc/avia-hx711.txt
index b3629405f568..4bee51d536e1 100644
--- a/Documentation/devicetree/bindings/iio/adc/avia-hx711.txt
+++ b/Documentation/devicetree/bindings/iio/adc/avia-hx711.txt
@@ -8,11 +8,21 @@ Required properties:
 		See Documentation/devicetree/bindings/gpio/gpio.txt
  - avdd-supply:	Definition of the regulator used as analog supply
 
+Optional properties:
+ - clock-frequency:	Frequency of PD_SCK
+			This setting affects the duration of the high value
+			phase of the clock (PD_SCK). The low value phase is
+			not affected since it is not relevant for the
+			measurement.
+			Minimum value allowed is 20 kHz because of maximum
+			high time of 50 microseconds.
+
 Example:
 weight@0 {
 	compatible = "avia,hx711";
 	sck-gpios = <&gpio3 10 GPIO_ACTIVE_HIGH>;
 	dout-gpios = <&gpio0 7 GPIO_ACTIVE_HIGH>;
 	avdd-suppy = <&avdd>;
+	clock-frequency = <100000>;
 };
 
-- 
2.1.4