Linux Driver APIs - devicetree

Devicetree API for Device Driver

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#include <linux/of.h>

0.Index
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- 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
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1.1使用compatible属性寻找节点
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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

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/** * 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
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/** * 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

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/** * 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
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2.1读取整形数据
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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
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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
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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
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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
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#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;}