Linux drivers development

This page summarizes all you need to know before starting to develop Linux drivers for your Armadeus board

Recommended reading before starting

We advise you to read (not necessarly understand ;-) ):

• Linux Device Drivers (3rd edition) book: http://lwn.net/Kernel/LDD3/

Adding your own drivers

Our custom drivers build is integrated to the Linux build system (kbuild). You can select, in the linux "menuconfig / xconfig" tool, which Armadeus drivers you want to add on your target.

 $ make linux-menuconfig

Device Drivers  --->
    Armadeus specific drivers  --->

Here is the way to add custom drivers:

• change current dir to your armadeus view
• in target/linux/modules/, add a directory for your driver (ex toto/)
• put reference to this directory in the target/linux/modules/Makefile and target/linux/modules/Kconfig files
• in toto/ put your driver source code and create 2 files, Kconfig and Makefile. (Use target/linux/modules/gpio/Makefile & Kconfig as examples.)

To compile all the custom modules, either launch:

 $ make -C target/linux/modules/

or

 $ make linux

Only make linux will install the modules in the target rootfs image

i.MX register access from driver

To access i.MX registers from your driver, please use the readw/readl/writew/writel helper functions. Take a look at at arch/arm/mach-mx2/apf27.c or arch/arm/mach-imx/apf9328.c to have examples.

Debug

• Activate debug messages (from pr_debug() function) on console:

 # echo 8 > /proc/sys/kernel/printk

Useful Links

• http://old.kernelnewbies.org/documents/kdoc/kernel-api/linuxkernelapi.html
• http://lwn.net/Articles/driver-porting/