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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