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Writing Device Drivers
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Driver Code Layout

The code for a device driver is usually divided into the following files:

  • Header files (.h files)

  • Source files (.c files)

  • Optional configuration file (driver.conf file)

Header Files

Header files provide the following definitions:

  • Data structures specific to the device, such as a structure representing the device registers

  • Data structures defined by the driver for maintaining state information

  • Defined constants, such as those representing the bits of the device registers

  • Macros, such as those defining the static mapping between the minor device number and the instance number

Some of the header file definitions, such as the state structure, might be needed only by the device driver. This information should go in private header files that are only included by the device driver itself.

Any information that an application might require, such as the I/O control commands, should be in public header files. These files are included by the driver and by any applications that need information about the device.

While there is no standard for naming private and public files, one convention is to name the private header file xximpl.h and the public header file xxio.h.

Source Files

A C source file (a .c file) for a device driver has the following responsibilities:

  • Contains the data declarations and the code for the entry points of the driver

  • Contains the #include statements that are needed by the driver

  • Declares extern references

  • Declares local data

  • Sets up the cb_ops and dev_ops structures

  • Declares and initializes the module configuration section, that is, the modlinkage(9S) and modldrv(9S) structures

  • Makes any other necessary declarations

  • Defines the driver entry points

Configuration Files

In general, the configuration file for a driver defines all of the properties that the driver needs. Entries in the driver configuration file specify possible device instances that the driver can probe for existence. Driver global properties can be set in the driver's configuration file. See the driver.conf(4) man page for more information.

Driver configuration files are required for devices that are not self-identifying.

Driver configuration files are optional for self-identifying devices (SID). For self-identifying devices, the configuration file can be used to add properties into SID nodes.

The following properties are examples of properties that are not set in the driver configuration file:

  • Drivers that use the SBus peripheral bus generally get property information from the SBus card. In cases where additional properties are needed, the driver configuration file can contain properties that are defined by sbus(4).

  • The properties of a PCI bus can generally be derived from the PCI configuration space. In cases where private driver properties are needed, the driver configuration file can contain properties that are defined by pci(4).

  • Drivers on the ISA bus can use additional properties that are defined by isa(4).

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  Published under the terms fo the Public Documentation License Version 1.01. Design by Interspire