On 14/11/16 23:12, Linus Walleij wrote: > On Mon, Nov 14, 2016 at 7:53 PM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: > >> It's about figuring out the setting of a "GPIO" that can't be changed from >> software. >> >> Devices sometimes, instead of a configuration bus like I2C or SPI, use >> simple input pins, that can either be set to high or low, to allow software >> the state of the device. The GPIO API is typically used to configure these pins. >> >> This works fine as long as the pin is connected to a GPIO. But sometimes the >> system designer decides that a settings does not need to be configurable, in >> this case the pin will be tied to logic low or high directly on the PCB >> without any GPIO controller being involved. >> >> Sometimes a driver wants to know how the pin is wired up so it can report to >> userspace this part runs in the following mode and the mode can't be >> changed. In a sense it is like a reverse GPIO hog. >> >> Considering that this is a common usecase the question was how this can be >> implemented in a driver independent way to avoid code duplication and >> slightly different variations of what is effectively the same DT/ACPI binding. >> >> E.g. lets say for a configurable pin you use >> >> range-gpio = <&gpio ...>; >> >> and for a static pin >> >> range-gpio-fixed = <1>; >> >> Or something similar. > > Aha I understand. > > Usually I feel we need not shoehorn stuff into GPIO because it is convenient, > it might be best to leave the GPIO optional and if it is not there, look for > a custom attribute that represents the "hogging" to 0/1. I think trying > to extend GPIO bindings to cover it is overgeneralization, instead go > for a local binding for this kind of devices. > > But mainly it is a question to the DT bindings maintainers. That's a reasonable approach, but I'd certainly like to see a generic binding to describe it. It's a pretty common situation. Seems more likely we'll get a device tree maintainer response if we cc them ;) So Mark, Rob and thoughts on this? Thanks, Jonathan > > Yours, > Linus Walleij > -- 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
