Kconfig syntax

转载：

http://www.rt-embedded.com/blog/archives/working-with-kconfig/

The Kconfig syntax

The Kconfig syntax is very simple and it is documented in the Documentation/kbuild/kconfig-language.txt file. Let’s review some of the basics by a few examples:

• An example from drivers/video/Kconfig:

config FB_CIRRUS
tristate "Cirrus Logic support"
depends on FB && (ZORRO || PCI)
select FB_CFB_FILLRECT
select FB_CFB_COPYAREA
select FB_CFB_IMAGEBLIT
---help---
This enables support for Cirrus Logic GD542x/543x based boards on
Amiga: SD64, Piccolo, Picasso II/II+, Picasso IV, or EGS Spectrum.

The example, defines a new variable in the name of CONFIG_FB_CIRRUS (note that the CONFIG_ prefix is added automatically and should be omitted from the Kconfig file itself). Let’s jump to the help section for a second. We can read that this configuration option enables support for various Cirrus Logic video cards. In the second line, we can see that this variable is in the type of “tristate”. It means that this configuration option has 3 possible states; Disabled, Enabled and Modulized. Each configuration option must have a type. The available types are: “bool“, “tristate“, “string“, “hex” or “int“. Each type has its own properties. The bool type can be either Enabled or Disabled. The string type will contain a list of characters. Thehex type will contain a hexadecimal representation of a number (usually used to assign hardware address and ids) and theint type contains numbers. Right next to the type, you’ll find the prompt string that represents the configuration option in the menu (or in the prompt). Next, shows the dependency of this configuration option. It means that this option will not be available for selection if the CONFIG_FB option is not enabled and either CONFIG_ZORRO or CONFIG_PCI are enabled. In this way, the driver developer can be sure that this driver will not be available unless the Frame Buffer framework is enabled and the target has either Zorro or PCI interfaces enabled (otherwise, the driver will fail to compile or run). The next lines, with theselect option, show options that the driver needs in order to operate correctly. In this example, we see that the driver requires a few Frame Buffer options to be enabled.