Open Source Summit Europe 2024

The Linux Kernel has two subsystems that handle external pins: pinctrl that handles function muxing and electrical characteristics, and GPIO that handles generic input/output usage on individual pins. Depending on how the hardware is implemented, the two could be completely separate, or deeply intertwined. This presentation will introduce the hardware integration designs , how they should map to the kernel subsystems. We will dive deeper into the latter case and show how the kernel subsystems can handle it properly with "strict" GPIO pin muxing, and what could happen if the driver isn't implemented correctly, using existing in-tree drivers.