加载流程分析
kconfig --> make menuconfig --> .config --> auto.conf autoconf.h
图形界面的make menuconfig加载的是kconfig，通常我们会编写kconfig语法来添加menuconfig图形界面的选择项，然后会生成.config，一般在arch/arm/make_xxxdeconfig会有默认，这个其实是默认加载项，如果想用自己的为默认加载，把生成的.config拷贝到此目录下即可，内核中所有文件都会引用include/config/auto.conf，并且内核中所有代码都会包含include/generated/autoconf.h此文件。
config语法
- config
config symbol
config options
config是关键字，表示一个配置选项的开始；紧跟着的是配置选项的名称，省略了前缀"CONFIG_"。
config TMPFS_POSIX_ACL
bool “Tmpfs POSIX Access Control Lists”
depends on TMPFS
select GENERIC_ACL
help
POSIX Access Control Lists (ACLs) support permissions for users and
groups beyond the owner/group/world scheme.
To learn more about Access Control Lists, visit the POSIX ACLs for
Linux website http://acl.bestbits.at/.
解析：config是关键字，表示一个配置选项的开始；紧跟着的TMPFS_POSIX_ACL是配置选项的名称，省略了前缀"CONFIG_"
bool表示变量类型，即"CONFIG_ TMPFS_POSIX_ACL "的类型，有5种类型：bool、 tristate、string、hex和int，其中tristate和string是基本的类型
bool变量的值： y和n
tristate变量的值： y、n和m (在make menuconfig图形界面中分别是 * , 空格, m)
string变量的值： 字符串
bool之后的字符串“Tmpfs POSIX Access Control Lists”是提示信息，在配置界面中上下移动光标选中它时，就可以通过按空格或回车键来设置CONFIG_ TMPFS_POSIX_ACL的值。
depends on：表示依赖于XXX，“depends on TMPFS”表示只有当TMPFS配置选项被选中时，当前配置选项的提示信息才会出现，才能设置当前配
- menuconfig
menuconfig symbol
config options
此关键字和前面的关键字很相似，但它在前面的基础上要求所有的子选项作为独立的行显示。
例如，在uplooking下创建了kconfig 文件修要在上一级目录的kconfig文件
cd /opt/UEA_10_08/s5p6818sdk_lzy1/Linux/src/linux-3.4/drivers/uplooking
vim ../Kconfig
# 在 source "drivers/base/Kconfig" 下面添加
source "drivers/uplooking/Kconfig
实例
menuconfig讲解
menuconfig UPLOOKING_MENU
bool "uplooking menu"
default y
help
If select uplooking menu display uplooking ops
if UPLOOKING_MENU
menu "uplooking"
config UPLOOKING_TRISTATE
tristate "this is uplooking tristate"
default m
help
If .......
config UPLOOKING_STRING
string "this is uplooking string"
default "this is string"
help
If .......
config UPLOOKING_INT
int "uplooing int"
default 100
depends on UPLOOKING_TRISTATE
help
If .......
bool讲解
config UPLOOKING_BOOL
bool "uplooing bool"
default y
select UPLOOKING_TRISTATE
help
If .......
endmenu # "uplooking"
choice讲解
choice
prompt "uplooking state"
default UPLOOING_OFF
config UPLOOING_OFF
bool "uplooking off"
help
if .......
config UPLOOKING_ON
bool "uplooking on"
help
if .......
endchoice
menuconfig UPLOOKING_MENU
bool "uplooking menu"
default y
help
If select uplooking menu display uplooking ops
if UPLOOKING_MENU
menu "uplooking"
config UPLOOKING_TRISTATE
tristate "this is uplooking tristate"
default m
help
If .......
config UPLOOKING_STRING
string "this is uplooking string"
default "this is string"
help
If .......
config UPLOOKING_INT
int "uplooing int"
default 100
depends on UPLOOKING_TRISTATE
help
If .......
config UPLOOKING_BOOL
bool "uplooing bool"
default y
select UPLOOKING_TRISTATE
help
If .......
endmenu # "uplooking"
choice
prompt "uplooking state"
default UPLOOING_OFF
config UPLOOING_OFF
bool "uplooking off"
help
if .......
config UPLOOKING_ON
bool "uplooking on"
help
if .......
endchoice