Linux Driver APIs - devicetree

Devicetree API for Device Driver

==========================================
#include <linux/of.h>

0.Index
=======

- 1.查找Devicetree节点
- 2.获取节点的属性和值
- 3.Sample Code

1.查找Devicetree节点
=================
1.1使用compatible属性寻找节点
-------------------------------------------
以@from节点为起点，用@compatible字符串匹配各节点compatible属性的值，返回
找到的devicetree节点。

/**
 * of_find_compatible_node - Find a node based on type and one of the
 *                                tokens in its "compatible" property
 * @from: The node to start searching from or NULL, the node
 * you pass will not be searched, only the next one
 * will; typically, you pass what the previous call
 * returned. of_node_put() will be called on it
 * @type: The type string to match "device_type" or NULL to ignore
 * @compatibleThe string to match to one of the tokens in the device
 * "compatible" list.
 *
 * Returns a node pointer with refcount incremented, use
 * of_node_put() on it when done.
 */
struct device_node *of_find_compatible_node(struct device_node *from,
		const char *type, const char *compatible)

Demo：

struct device_node *of_node;
/* Searching from root node */
of_node = of_find_compatible_node(NULL, NULL, "vendor,chip");

/* Searching child node from an existing node */
struct device_node *parent = of_node; /* node that got from other code*/
of_node = of_find_compatible_node(parent, NULL, "vendor,chip");

1.2使用节点名称寻找

----------------------------

/**
 * of_find_node_by_name - Find a node by its "name" property
 * @from: The node to start searching from or NULL, the node
 * you pass will not be searched, only the next one
 * will; typically, you pass what the previous call
 * returned. of_node_put() will be called on it
 * @name: The name string to match against
 *
 * Returns a node pointer with refcount incremented, use
 * of_node_put() on it when done.
 */
struct device_node *of_find_node_by_name(struct device_node *from,
		const char *name)

Demo:

&i2c1 {
touchpanel {
property-a = <1>;
property-b = "string a";
};
};

struct device_node *of_node;
of_node = of_find_node_by_name(NULL, "touchpanel");

1.3使用phandle寻找节点
--------------------------------

/**
 * of_find_node_by_phandle - Find a node given a phandle
 * @handle: phandle of the node to find
 *
 * Returns a node pointer with refcount incremented, use
 * of_node_put() on it when done.
 */
struct device_node *of_find_node_by_phandle(phandle handle)

1.4通过属性名称来寻找节点

-------------------------------------

/**
 * of_find_node_with_property - Find a node which has a property with
 *                                   the given name.
 * @from: The node to start searching from or NULL, the node
 * you pass will not be searched, only the next one
 * will; typically, you pass what the previous call
 * returned. of_node_put() will be called on it
 * @prop_name:The name of the property to look for.
 *
 * Returns a node pointer with refcount incremented, use
 * of_node_put() on it when done.
 */
struct device_node *of_find_node_with_property(struct device_node *from,
		const char *prop_name)

2.获取节点的属性的值
====================
2.1读取整形数据
---------------------

int of_property_read_u8(const struct device_node *np,
		const char *propname, u8 *out_value)

int of_property_read_u16(const struct device_node *np,
		const char *propname, u16 *out_value)

int of_property_read_u32(const struct device_node *np,
		const char *propname, u32 *out_value)

int of_property_read_u64(const struct device_node *np,
		const char *propname, u64 *out_value);

2.2读取整型数组
---------------------

int of_property_read_u8_array(const struct device_node *np,
		const char *propname, u8 *out_values, size_t sz)


int of_property_read_u16_array(const struct device_node *np,
		const char *propname, u16 *out_values, size_t sz)
	

int of_property_read_u32_array(const struct device_node *np,
		const char *propname, u32 *out_values, size_t sz)

2.3读取整型数组中某个索引位置的数据
----------------------------------------------------

static inline int of_property_read_u32_index(const struct device_node *np,
		const char *propname, u32 index, u32 *out_value)

2.4读取字符串数据
-------------------------

int of_property_read_string(struct device_node *np,
		const char *propname, const char **out_string);


int of_property_read_string_index(struct device_node *np,
		const char *propname, int index, const char **output);


int of_property_match_string(struct device_node *np,
		const char *propname, const char *string);


int of_property_count_strings(struct device_node *np,
		const char *propname);

3.Sample Code
============
#include <linux/of.h>

static int samp_parse_dts(struct device *dev)
{
	struct device_node *of_node = dev->of_node;
	const char *compatible = "vendor,x";
	u32 val0;
	u8 val1;
	const char *string;

	if (!of_node)
		return -EINVAL;

	if (!of_device_is_compatible(of_node, compatible))
		return -ENODEV;

	if (of_property_read_u32(of_node, "vendor,val0", &val0))
		/* fail */
		val0 = -1;

	if (of_property_read_u8(of_node, "vendor,val0", &val1))
		/* fail */
		val1 = -1;

	if (of_property_read_string(of_node, "vendor,str", &string)
		string = NULL;
	return 0;
}