On Thu, 12 Oct 2017 12:40:10 +0200 Lukas Wunner <lukas@xxxxxxxxx> wrote: > 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@xxxxxxxxx> Makes sense to me. Acked-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > --- > Changes v1 -> v2: > > - Newly inserted patch. > > .../devicetree/bindings/common-properties.txt | 26 ++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > 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>; > +}; -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
