The DMA engine API

The DMA engine is a generic kernel framework for developing a DMA controller driver. The main goal of DMA is offloading the CPU when it comes to copy memory. One delegates a transaction (I/O data transfers) to the DMA engine by the use of channels. A DMA engine, through its driver/API, exposes a set of channels that can be used by other devices (slaves). The DMA Engine layout is shown in the following diagram:

DMA Engine layout

Here, we will simply walk through the (slave) API, which is applicable for slave DMA usage only. The mandatory header here is as follows:

 #include <linux/dmaengine.h> 

Using the slave DMA is straightforward, and consists of the following steps:

1. Allocate a DMA slave channel.
2. Set slave- and controller-specific parameters.
3. Get a descriptor for the transaction.
4. Submit the transaction.
5. Issue pending requests and wait for callback notification.

Note

One can see a DMA channel as a highway for I/O data transfer.

Allocating a DMA slave channel

One requests a...