Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Linus Torvalds included patches into the mainline tree which implement a stable userspace driver API into the Linux kernel.
The stable driver API was already announced a year ago by Greg Kroah-Hartman. Now the last patches where uploaded and the API was included in Linus’ tree. The idea of the API is to make life easier for driver developers:
"This interface allows the ability to write the majority of a driver in userspace with only a very small shell of a driver in the kernel itself. It uses a char device and sysfs to interact with a userspace process to process interrupts and control memory accesses."
Since future drivers using this API will run mainly in userspace there is no need to open up the source code for these parts. Also, drivers can be re-used even after kernel changes because the API will remain stable.
The background motivation for the inclusion of such a stable API comes form the embedded world.