Provide more guidance to differentiate between recommendations for names of lines which are hard-wired to on-board devices, versus recommendations for names of lines which are connected to general-purpose pin headers. Signed-off-by: Trevor Woerner <twoerner@xxxxxxxxx> --- .../devicetree/bindings/gpio/gpio.txt | 41 +++++++++++++------ 1 file changed, 29 insertions(+), 12 deletions(-) diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt index 5663e71b751f..d82c32217fff 100644 --- a/Documentation/devicetree/bindings/gpio/gpio.txt +++ b/Documentation/devicetree/bindings/gpio/gpio.txt @@ -154,18 +154,35 @@ of the GPIOs that can't be used. Optionally, a GPIO controller may have a "gpio-line-names" property. This is an array of strings defining the names of the GPIO lines going out of the -GPIO controller. This name should be the most meaningful producer name -for the system, such as a rail name indicating the usage. Package names -such as pin name are discouraged: such lines have opaque names (since they -are by definition generic purpose) and such names are usually not very -helpful. For example "MMC-CD", "Red LED Vdd" and "ethernet reset" are -reasonable line names as they describe what the line is used for. "GPIO0" -is not a good name to give to a GPIO line. Placeholders are discouraged: -rather use the "" (blank string) if the use of the GPIO line is undefined -in your design. The names are assigned starting from line offset 0 from -left to right from the passed array. An incomplete array (where the number -of passed named are less than ngpios) will still be used up until the last -provided valid line index. +GPIO controller. + +For lines which are routed to on-board devices, this name should be +the most meaningful producer name for the system, such as a rail name +indicating the usage. Package names, such as a pin name, are discouraged: +such lines have opaque names (since they are by definition general-purpose) +and such names are usually not very helpful. For example "MMC-CD", "Red LED +Vdd" and "ethernet reset" are reasonable line names as they describe what +the line is used for. "GPIO0" is not a good name to give to a GPIO line +that is hard-wired to a specific device. + +However, in the case of lines that are routed to a general purpose header +(e.g. the Raspberry Pi 40-pin header), and therefore are not hard-wired to +specific devices, using a pin number or the names on the header is fine +provided these are real (preferably unique) names. Using an SoC's pad name +or package name, or names made up from kernel-internal software constructs, +are strongly discouraged. For example "pin8 [gpio14/uart0_txd]" is fine +if the board's documentation labels pin 8 as such. However "PortB_24" (an +example of a name from an SoC's reference manual) would not be desirable. + +In either case placeholders are discouraged: rather use the "" (blank +string) if the use of the GPIO line is undefined in your design. Ideally, +try to add comments to the dts file describing the naming the convention +you have chosen, and specifying from where the names are derived. + +The names are assigned starting from line offset 0, from left to right, +from the passed array. An incomplete array (where the number of passed +names is less than ngpios) will be used up until the last provided valid +line index. Example: -- 2.36.0.rc2.17.g4027e30c53
