The concept of completion

This section will briefly describe completion and the necessary part of its API that the DMA transfer uses. For a complete description, please feel free to have a look at the kernel documentation at Documentation/scheduler/completion.txt. A common pattern in kernel programming involves initiating some activity outside the current thread, then waiting for that activity to complete.

Completion is a good alternative to sleep() when waiting for a buffer to be used. It is suitable for sensing data, which is exactly what the DMA callback does.

Working with completion requires this header:

<linux/completion.h>  

Like other kernel facility data structures, one can create instances of the struct completion structure either statically or dynamically:

• Static declaration and initialization look like this:

 DECLARE_COMPLETION(my_comp); 

• Dynamic allocation looks like this:

struct completion my_comp; 
init_completion(&my_comp); 

When the driver begins some work whose completion...