一、ubuntu设备树编译方法
- ubuntu安装dtc工具
sudo apt-get install device-tree-compiler- 使用dtc工具编译设备树源文件
dtc -I dts -O dtb -o test.dtb test.dts- 使用dtc工具反编译设备树二进制文件
dtc -I dtb -O dts -o test.dts test.dtb二、解析设备树并注册平台设备of_platform_populate
// 文件arch/arm/kernel/setup.c
static int __init customize_machine(void)
{
of_iommu_init();
if (machine_desc->init_machine)
machine_desc->init_machine();
#ifdef CONFIG_OF
else
of_platform_populate(NULL, of_default_bus_match_table,
NULL, NULL);
#endif
return 0;
}const struct of_device_id of_default_bus_match_table[] = {
{ .compatible = "simple-bus", },
{ .compatible = "simple-mfd", },
#ifdef CONFIG_ARM_AMBA
{ .compatible = "arm,amba-bus", },
#endif /* CONFIG_ARM_AMBA */
{} /* Empty terminated list */
}; - 该函数为arm平台板级初始化入口，调用init_machine板级初始化
- 调用of_platform_populate函数解析设备树创建注册平台设备,此时传入参数of_default_bus_match_table
// 文件drivers/of/platform.c
int of_platform_populate(struct device_node *root,
const struct of_device_id *matches,
const struct of_dev_auxdata *lookup,
struct device *parent)
{
struct device_node *child;
int rc = 0;
root = root ? of_node_get(root) : of_find_node_by_path("/");
if (!root)
return -EINVAL;
for_each_child_of_node(root, child) {
rc = of_platform_bus_create(child, matches, lookup, parent, true);
if (rc)
break;
}
of_node_set_flag(root, OF_POPULATED_BUS);
of_node_put(root);
return rc;
}- 遍历设备树root的子结点，调用of_platform_bus_create创建注册Platform device
// 文件drivers/of/platform.c
static int of_platform_bus_create(struct device_node *bus,
const struct of_device_id *matches,
const struct of_dev_auxdata *lookup,
struct device *parent, bool strict)
{
......
dev = of_platform_device_create_pdata(bus, bus_id, platform_data, parent);
if (!dev || !of_match_node(matches, bus))
return 0;
for_each_child_of_node(bus, child) {
pr_debug(" create child: %s\n", child->full_name);
rc = of_platform_bus_create(child, matches, lookup, &dev->dev, strict);
if (rc) {
of_node_put(child);
break;
}
}
......
}- 根据结点bus创建platform device
- 如果dev创建失败或者node id与of_default_bus_match_table匹配，则递归搜索子结点
小结，在板级初始化时，of_platform_populate会去解析设备树为platform device有两种情况：
- 根结点下的子结点
- 如果子节点的compiltale属性与of_default_bus_match_table匹配，则递归解析该结点下的子结点
三、I2C设备树的解析
// I2C设备树实例
&i2c2 {
clock-frequency = <100000>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_i2c2>;
status = "okay";
codec: wm8960@1a {
compatible = "wlf,wm8960";
reg = <0x1a>;
clocks = <&clks IMX6QDL_CLK_CKO>;
//clocks = <&clks 201>;
clock-names = "mclk";
DCVDD-supply = <®_audio>;
DBVDD-supply = <®_audio>;
AVDD-supply = <®_audio>;
CPVDD-supply = <®_audio>;
MICVDD-supply = <®_audio>;
PLLVDD-supply = <®_audio>;
SPKVDD1-supply = <®_audio>;
SPKVDD2-supply = <®_audio>;
wlf,shared-lrclk;
/* capless; */
// amic-mono;
};- 父结点将作为I2C控制器设备，通过i2c_add_numbered_adapter函数注册到系统中
- 子结点将被解析为I2C从设备，注册到I2C总线上去，进而与对应的I2C驱动相匹配
int i2c_add_numbered_adapter(struct i2c_adapter *adap)
{
if (adap->nr == -1) /* -1 means dynamically assign bus id */
return i2c_add_adapter(adap);
return __i2c_add_numbered_adapter(adap);
}
EXPORT_SYMBOL_GPL(i3c_add_numbered_adapter);- i2c_add_numbered_adapter调用__i2c_add_numbered_adapter，然后__i2c_add_numbered_adapter在调用i2c_register_adapter注册I2C控制器
static int i2c_register_adapter(struct i2c_adapter *adap)
{
......
exit_recovery:
/* create pre-declared device nodes */
of_i2c_register_devices(adap);
acpi_i2c_register_devices(adap);
acpi_i2c_install_space_handler(adap);
if (adap->nr < __i2c_first_dynamic_bus_num)
i2c_scan_static_board_info(adap);
/* Notify drivers */
mutex_lock(&core_lock);
bus_for_each_drv(&i2c_bus_type, NULL, adap, __process_new_adapter);
mutex_unlock(&core_lock);
return 0;
out_list:
mutex_lock(&core_lock);
idr_remove(&i2c_adapter_idr, adap->nr);
mutex_unlock(&core_lock);
return res;
}- i2c_register_adapter调用of_i2c_register_devices解析设备树创建i2c_client，并注册到I2C总线
static void of_i2c_register_devices(struct i2c_adapter *adap)
{
struct device_node *node;
/* Only register child devices if the adapter has a node pointer set */
if (!adap->dev.of_node)
return;
dev_dbg(&adap->dev, "of_i2c: walking child nodes\n");
for_each_available_child_of_node(adap->dev.of_node, node)
of_i2c_register_device(adap, node);
}- 遍历设备树子节点，调用of_i2c_register_device创建i2c_client
static struct i2c_client *of_i2c_register_device(struct i2c_adapter *adap,
struct device_node *node)
{
struct i2c_client *result;
struct i2c_board_info info = {};
struct dev_archdata dev_ad = {};
const __be32 *addr;
int len;
dev_dbg(&adap->dev, "of_i2c: register %s\n", node->full_name);
if (of_modalias_node(node, info.type, sizeof(info.type)) < 0) {
dev_err(&adap->dev, "of_i2c: modalias failure on %s\n",
node->full_name);
return ERR_PTR(-EINVAL);
}
addr = of_get_property(node, "reg", &len);
if (!addr || (len < sizeof(int))) {
dev_err(&adap->dev, "of_i2c: invalid reg on %s\n",
node->full_name);
return ERR_PTR(-EINVAL);
}
info.addr = be32_to_cpup(addr);
if (info.addr > (1 << 10) - 1) {
dev_err(&adap->dev, "of_i2c: invalid addr=%x on %s\n",
info.addr, node->full_name);
return ERR_PTR(-EINVAL);
}
info.of_node = of_node_get(node);
info.archdata = &dev_ad;
if (of_get_property(node, "wakeup-source", NULL))
info.flags |= I2C_CLIENT_WAKE;
result = i2c_new_device(adap, &info);
if (result == NULL) {
dev_err(&adap->dev, "of_i2c: Failure registering %s\n",
node->full_name);
of_node_put(node);
return ERR_PTR(-EINVAL);
}
return result;
}- 解析设备树填充i2c_board_info结构体
- 调用i2c_new_device创建注册i2c_client