Learning how not to write GPIO client drivers
There are situations where writing user space code would achieve the same goals as writing kernel drivers. Moreover, the GPIO framework is one of the most used frameworks in the user space. It then goes without saying that there are several possibilities to deal with it in the user space, some of which we will introduce in this chapter.
Goodbye to the legacy GPIO sysfs interface
Sysfs has ruled GPIO management from the user space for quite a long time now. Though it is scheduled for removal, the sysfs GPIO interface still has a few days ahead of it. CONFIG_GPIO_SYSFS can still enable it, but its use is discouraged, and it will be removed from mainline Linux. This interface allows managing and controlling GPIOs through a set of files. It is located at /sys/class/gpio/, and the following are the common directory paths and attributes that are involved:
/sys/class/gpio/: This is where it all starts. There are two special files...
