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authorLukas Wunner <lukas@wunner.de>2017-10-12 13:40:10 +0300
committerLinus Walleij <linus.walleij@linaro.org>2017-10-19 23:33:11 +0300
commit1f63fab955dbcb8f6db56d67a4c63fc0746e4fe1 (patch)
tree2335c929d016f9878e1199885e87ade31c6cb032 /Documentation/devicetree/bindings/common-properties.txt
parent5048f0aefb96fe3fd468002c879d7a5918336b1f (diff)
downloadlinux-1f63fab955dbcb8f6db56d67a4c63fc0746e4fe1.tar.xz
dt-bindings: Document common property for daisy-chained devices
Many serially-attached GPIO and IIO devices are daisy-chainable. Examples for GPIO devices are Maxim MAX3191x and TI SN65HVS88x: https://datasheets.maximintegrated.com/en/ds/MAX31913.pdf http://www.ti.com/lit/ds/symlink/sn65hvs880.pdf Examples for IIO devices are TI DAC128S085 and TI DAC161S055: http://www.ti.com/lit/ds/symlink/dac128s085.pdf http://www.ti.com/lit/ds/symlink/dac161s055.pdf We already have drivers for daisy-chainable devices in the tree but their devicetree bindings are somewhat inconsistent and ill-named: The gpio-74x164.c driver uses "registers-number" to convey the number of devices in the daisy-chain. (Sans vendor prefix, multiple vendors sell compatible versions of this chip.) The gpio-pisosr.c driver takes a different approach and calculates the number of devices in the daisy-chain by dividing the common "ngpios" property (Documentation/devicetree/bindings/gpio/gpio.txt) by 8 (which assumes that each chip has 8 inputs). Let's standardize on a common "#daisy-chained-devices" property. That name was chosen because it's the term most frequently used in datasheets. (A less frequently used synonym is "cascaded devices".) Signed-off-by: Lukas Wunner <lukas@wunner.de> Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> Acked-by: Rob Herring <robh@kernel.org> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
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-rw-r--r--Documentation/devicetree/bindings/common-properties.txt26
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diff --git a/Documentation/devicetree/bindings/common-properties.txt b/Documentation/devicetree/bindings/common-properties.txt
index 697714f8d75c..a3448bfa1c82 100644
--- a/Documentation/devicetree/bindings/common-properties.txt
+++ b/Documentation/devicetree/bindings/common-properties.txt
@@ -1,4 +1,8 @@
Common properties
+=================
+
+Endianness
+----------
The Devicetree Specification does not define any properties related to hardware
byteswapping, but endianness issues show up frequently in porting Linux to
@@ -58,3 +62,25 @@ dev: dev@40031000 {
...
little-endian;
};
+
+Daisy-chained devices
+---------------------
+
+Many serially-attached GPIO and IIO devices are daisy-chainable. To the
+host controller, a daisy-chain appears as a single device, but the number
+of inputs and outputs it provides is the sum of inputs and outputs provided
+by all of its devices. The driver needs to know how many devices the
+daisy-chain comprises to determine the amount of data exchanged, how many
+inputs and outputs to register and so on.
+
+Optional properties:
+ - #daisy-chained-devices: Number of devices in the daisy-chain (default is 1).
+
+Example:
+gpio@0 {
+ compatible = "name";
+ reg = <0>;
+ gpio-controller;
+ #gpio-cells = <2>;
+ #daisy-chained-devices = <3>;
+};