Our hackerspace’s access-control-system (for unlocking the door) uses a few mcp23017 port expanders for input/output handling of different sensors and actors. When I started working on this, the mcp23s08 driver (which also supports the mcp23017) was not yet enabled in Debian’s arm build. I requested it to be enabled in Debian Bug #845064, which got recently fixed by Ben Hutchings. As a quick hack to solve the problem I took the driver and ripped it out of the kernel, so that I can build it externally. Read more →