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| author | Lukas Wunner <lukas@wunner.de> | 2017-10-12 12:40:10 +0200 |
|---|---|---|
| committer | Linus Walleij <linus.walleij@linaro.org> | 2017-10-19 22:33:11 +0200 |
| commit | 1f63fab955dbcb8f6db56d67a4c63fc0746e4fe1 (patch) | |
| tree | 2335c929d016f9878e1199885e87ade31c6cb032 /Documentation/devicetree/bindings/common-properties.txt | |
| parent | 5048f0aefb96fe3fd468002c879d7a5918336b1f (diff) | |
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>
Diffstat (limited to 'Documentation/devicetree/bindings/common-properties.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/common-properties.txt | 26 |
1 files changed, 26 insertions, 0 deletions
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>; +}; |