The Road to Linux Kernel - platform driver interface

platform driver驱动，下面这样的方式是其中一种注册方式, 驱动会注册到形如**__initcall**的段中，然后在start_kernel时进行调用。

static struct platform_driver tegra_ahb_driver = {
	.probe = tegra_ahb_probe,
	.driver = {
		.name = DRV_NAME,
		.of_match_table = tegra_ahb_of_match,
		.pm = &tegra_ahb_pm,
	},
};
module_platform_driver(tegra_ahb_driver);

调用关系如下，在initcall_levels这个结构体中，保存了每个section的起始与结束地址

static initcall_entry_t *initcall_levels[] __initdata = {
	__initcall0_start,
	__initcall1_start,
	__initcall2_start,
	__initcall3_start,
	__initcall4_start,
	__initcall5_start,
	__initcall6_start,
	__initcall7_start,
	__initcall_end,
};

start_kernel

arch_call_rest_init

rest_init

kernel_init

kernel_init_freeable

do_basic_setup

do_initcalls

static void __init do_initcall_level(int level)
{
	initcall_entry_t *fn;

	strcpy(initcall_command_line, saved_command_line);
	parse_args(initcall_level_names[level],
		   initcall_command_line, __start___param,
		   __stop___param - __start___param,
		   level, level,
		   NULL, &repair_env_string);

	trace_initcall_level(initcall_level_names[level]);
	for (fn = initcall_levels[level]; fn < initcall_levels[level+1]; fn++)
		do_one_initcall(initcall_from_entry(fn));
}

其中就会调用platform_driver_register，调用关系如下, 最终就会调用之前注册的probe函数，观察probe函数的入参dev，那么dev是什么时候分配的？

platform_driver_register

__platform_driver_register

driver_register

bus_add_driver

driver_attach

bus_for_each_dev

__driver_attach

device_driver_attach

driver_probe_device

driver_probe_device

really_probe

if (dev->bus->probe) {
	ret = dev->bus->probe(dev);
	if (ret)
		goto probe_failed;
} else if (drv->probe) {
	ret = drv->probe(dev);
	if (ret)
		goto probe_failed;
}

以arm64为例，简单过一下通过device tree动态生成device的过程

• 解析设备树

start_kernel

setup_arch

setup_machine_fdt

unflatten_device_tree

__unflatten_device_tree

unflatten_dt_nodes

populate_node

of_node_init

populate_properties

• 生成platform device

of_platform_default_populate_init

of_platform_default_populate

of_platform_populate

of_platform_bus_create

of_platform_device_create_pdata

of_device_alloc

of_device_add

device_add