Book Image

Mastering Linux Device Driver Development

By : John Madieu
Book Image

Mastering Linux Device Driver Development

By: John Madieu

Overview of this book

Linux is one of the fastest-growing operating systems around the world, and in the last few years, the Linux kernel has evolved significantly to support a wide variety of embedded devices with its improved subsystems and a range of new features. With this book, you’ll find out how you can enhance your skills to write custom device drivers for your Linux operating system. Mastering Linux Device Driver Development provides complete coverage of kernel topics, including video and audio frameworks, that usually go unaddressed. You’ll work with some of the most complex and impactful Linux kernel frameworks, such as PCI, ALSA for SoC, and Video4Linux2, and discover expert tips and best practices along the way. In addition to this, you’ll understand how to make the most of frameworks such as NVMEM and Watchdog. Once you’ve got to grips with Linux kernel helpers, you’ll advance to working with special device types such as Multi-Function Devices (MFD) followed by video and audio device drivers. By the end of this book, you’ll be able to write feature-rich device drivers and integrate them with some of the most complex Linux kernel frameworks, including V4L2 and ALSA for SoC.
Table of Contents (19 chapters)
1
Section 1:Kernel Core Frameworks for Embedded Device Driver Development
6
Section 2: Multimedia and Power Saving in Embedded Linux Systems
13
Section 3: Staying Up to Date with Other Linux Kernel Subsystems

PCI and Direct Memory Access (DMA)

In order to speed up data transfer and offload the CPU by allowing it not to perform heavy memory copy operations, both the controller and the device can be configured to perform Direct Memory Access (DMA), which is a means by which data is exchanged between device and host without the CPU being involved. Depending on the root complex, the PCI address space can be either 32 or 64 bits.

System memory regions that are the source or destination of DMA transfers are called DMA buffers. However, DMA buffer memory ranges depend on the size of the bus address. This originated from the ISA bus, which was 24-bits wide. In such a bus, DMA buffers could live only in the bottom 16 MB of system memory. This bottom memory is also referred to as ZONE_DMA. However, PCI buses do not have such limitations. While the classic PCI bus supports 32-bit addressing, PCIe extended this to 64 bits. Thus, two different address formats can be used: the 32-bit address format...