I'm working on writing a driver for custom hardware, but I'm not sure the best way to expose the features of the hardware to userspace. The hardware in question is basically a configurable industrial GPIO board, but it has additional features that don't seem to map well to the libgpio subsystem. The board has a set of output pins that can be treated like normal GPIO pins. The input pins, however, have additional configuration that can be set by a user. For example, the inputs can be configured for different input voltage levels, such as 24 Vdc, 110 Vac at 60 Hz, 220 Vac at 50 Hz, etc. Debounce times can also be configured. The hardware also has a FIFO buffer that records the state of all input pins, as well as a free running counter (FRC), when any input value changes. What is a reasonable way to expose the voltage and debounce configuration to userspace? Or the FIFO? Presently, I have an initial driver that creates a character device in /dev and uses ioctls so a user can provide configuration, read input/output state, and read the FIFO. There is also a custom sysfs interface to access the same configuration values and data.The sysfs interface is manily to provide something easier to use from shell, all the functionality is also duplicated in the ioctl interface. I plan on adding access to the input/output states through libgpio, but have not finished this yet. I'd like to get this driver in a state where it could be merged upstream, but I'm not sure that a custom sysfs class or ioctls are the right way to go. Is there a better way for userspace to provide this configuration, or access to the FIFO? This is the first kernel driver I've worked on, so it's possible there is an obvious way to implement this that I just haven't seen yet. Or maybe this hardware is just too specific and doesn't make a good candidate for pushing upstream. I'd appreciate any suggestions or ideas! Thanks, Robert