Linux drivers generalities

This page summarizes all the important things to know when talking about Linux drivers in general.

What

Linux drivers are the piece of code running inside the kernel itself that are assigned to a specific peripheral driving. They can exist in 2 forms:

• they can be statically linked to the kernel image. In that case we refer to static drivers
• or they can be compiled as loadable modules (the famous .ko files)

When compiled as "static" (<*> in Linux menuconfig) they are integrated in the Linux image (buildroot/binaries/armadeus/linux-kernel-2.6.xx-arm.bin), so when you reflash your kernel, the driver are immediately available. But if you don't use them, the consume some place in memory (RAM).

When compiled as "module" (<M> in Linux menuconfig) they can be dynamically loaded at runtime, when necessary. For example if you need to load the FPGA at a particular time you can do a:

# modprobe fpga_loader

or

# insmod /lib/modules/drivers/armadeus/fpga/fpga_loader.ko

modprobe knows where to find the corresponding .ko file and find all its dependencies thanks to the /lib/modules/2.6.2x/modules.dep file. So If you compile new drivers as module and copy them on your board "manually" (ie TFTP or NFS), don't forget to update /lib/modules/2.6.2x/modules.dep too. On your Host this file can be found in buildroot/project_build_arm/armadeus/root/lib/modules/2.6.2x/modules.dep.