Linux设备驱动之platform总线.docVIP

LINUX设备驱动之platform总线 -------------------------------------------------------------- 分析linux内核源码，版本号为2.6.32.3 ------------------------------------------------------------- 阅读本文之前，如果你对设备驱动模型还不了解，请先阅读本站设备驱动模型相关文章。 Platform总线是kernel中的一种虚拟总线，2.6版本很多驱动都用它来实现。 一．Platform初始化 系统启动时初始化时创建了platform_bus设备和platform_bus_type总线： 内核初始化函数 /* * Ok, the machine is now initialized. None of the devices * have been touched yet, but the CPU subsystem is up and * running, and memory and process management works. * * Now we can finally start doing some real work.. */ static void __init do_basic_setup(void) { cpuset_init_smp(); usermodehelper_init(); init_tmpfs(); driver_init(); //go in. init_irq_proc(); do_ctors(); do_initcalls(); } /** * driver_init - initialize driver model. * * Call the driver model init functions to initialize their * subsystems. Called early from init/main.c. */ void __init driver_init(void) { /* These are the core pieces */ devtmpfs_init(); devices_init(); buses_init(); classes_init(); firmware_init(); hypervisor_init(); /* These are also core pieces, but must come after the * core core pieces. */ platform_bus_init(); //hackson,goin. system_bus_init(); cpu_dev_init(); memory_dev_init(); } 我们看看platform_bus_init()函数： int __init platform_bus_init(void) { int error; early_platform_cleanup(); error = device_register(platform_bus); if (error) return error; error = bus_register(platform_bus_type); if (error) device_unregister(platform_bus); return error; } device_register(platform_bus)中的platform_bus如下： struct device platform_bus = { .init_name = platform, }; 改函数把设备名为platform 的设备platform_bus注册到系统中，其他的platform的设备都会以它为parent。它在sysfs中目录下.即 /sys/devices/platform。 接着bus_register(platform_bus_type)注册了platform_bus_type总线，看一下改总线的定义： struct bus_type platform_bus_type = { .name = platform, .dev_attrs = platform_dev_attr