linux-kernel - [PATCH 1/1] dt-bindings: adc-keys.txt: clarify description

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Date:   Tue, 22 Dec 2020 12:08:15 +0100
From:   Heinrich Schuchardt <xypron.glpk@....de>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Heinrich Schuchardt <xypron.glpk@....de>
Subject: [PATCH 1/1] dt-bindings: adc-keys.txt: clarify description

The current description of ADC keys is not precise enough.

"when this key is pressed" leaves it open if a key is considered pressed
below or above the threshold. This has led to confusion:
drivers/input/keyboard/adc-keys.c ignores the meaning of thresholds and
sets the key that is closest to press-threshold-microvolt.

This patch nails down the definitions and provides an interpretation of the
supplied example.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@....de>
---
I know that this file needs to be converted to YAML. But lets first get the
text right.
---
 .../devicetree/bindings/input/adc-keys.txt    | 22 +++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/Documentation/devicetree/bindings/input/adc-keys.txt b/Documentation/devicetree/bindings/input/adc-keys.txt
index e551814629b4..6c8be6a9ace2 100644
--- a/Documentation/devicetree/bindings/input/adc-keys.txt
+++ b/Documentation/devicetree/bindings/input/adc-keys.txt
@@ -5,7 +5,8 @@ Required properties:
  - compatible: "adc-keys"
  - io-channels: Phandle to an ADC channel
  - io-channel-names = "buttons";
- - keyup-threshold-microvolt: Voltage at which all the keys are considered up.
+ - keyup-threshold-microvolt: Voltage above or equal to which all the keys are
+			      considered up.

 Optional properties:
 	- poll-interval: Poll interval time in milliseconds
@@ -17,7 +18,12 @@ Each button (key) is represented as a sub-node of "adc-keys":
 Required subnode-properties:
 	- label: Descriptive name of the key.
 	- linux,code: Keycode to emit.
-	- press-threshold-microvolt: Voltage ADC input when this key is pressed.
+	- press-threshold-microvolt: voltage above or equal to which this key is
+				     considered pressed.
+
+No two values of press-threshold-microvolt may be the same.
+All values of press-threshold-microvolt must be less than
+keyup-threshold-microvolt.

 Example:

@@ -47,3 +53,15 @@ Example:
 			press-threshold-microvolt = <500000>;
 		};
 	};
+
++--------------------------------+------------------------+
+| 2.000.000 <= value             | no key pressed         |
++--------------------------------+------------------------+
+| 1.500.000 <= value < 2.000.000 | KEY_VOLUMEUP pressed   |
++--------------------------------+------------------------+
+| 1.000.000 <= value < 1.500.000 | KEY_VOLUMEDOWN pressed |
++--------------------------------+------------------------+
+|   500.000 <= value < 1.000.000 | KEY_ENTER pressed      |
++--------------------------------+------------------------+
+|              value <   500.000 | no key pressed         |
++--------------------------------+------------------------+
--
2.29.2