內核regmap機制

內核版本：3.10.92

內核3.1引入了一套新的API機制：regmap，主要爲I2C，SPI，IRQ等操作提供統一接口，提高代碼可重用性，減少重複邏輯。

以I2C爲例：

要讓設備跟I2C通信，以前的辦法是調用i2c_transfer接口，其實regmap最終還是調用到i2c_transfer，只不過中間加了一層緩衝，這樣統一了接口，減少了底層I/O的操作次數。

在初始化之前，要先填充regmap_config結構體。

先看看定義：

struct regmap_config {
	const char *name;

	int reg_bits;//寄存器地址位數，必須配置
	int reg_stride;
	int pad_bits;//寄存器和值之間的填充位數
	int val_bits;//寄存器值的位數，必須配置

	bool (*writeable_reg)(struct device *dev, unsigned int reg);
	bool (*readable_reg)(struct device *dev, unsigned int reg);
	bool (*volatile_reg)(struct device *dev, unsigned int reg);
	bool (*precious_reg)(struct device *dev, unsigned int reg);
	regmap_lock lock;
	regmap_unlock unlock;
	void *lock_arg;

	int (*reg_read)(void *context, unsigned int reg, unsigned int *val);
	int (*reg_write)(void *context, unsigned int reg, unsigned int val);

	bool fast_io;

	unsigned int max_register;
	const struct regmap_access_table *wr_table;
	const struct regmap_access_table *rd_table;
	const struct regmap_access_table *volatile_table;
	const struct regmap_access_table *precious_table;
	const struct reg_default *reg_defaults;
	unsigned int num_reg_defaults;
	enum regcache_type cache_type;
	const void *reg_defaults_raw;
	unsigned int num_reg_defaults_raw;

	u8 read_flag_mask;
	u8 write_flag_mask;

	bool use_single_rw;

	enum regmap_endian reg_format_endian;
	enum regmap_endian val_format_endian;

	const struct regmap_range_cfg *ranges;
	unsigned int num_ranges;
};

註冊：

struct regmap *devm_regmap_init_i2c(struct i2c_client *i2c,
				    const struct regmap_config *config)

讀寫I2C：

int regmap_read(struct regmap *map, unsigned int reg, unsigned int *val)；//讀取reg中的值，保存在val中
int regmap_raw_read(struct regmap *map, unsigned int reg, void *val,
		    size_t val_len)；	//從reg中讀取val_len長度的數據，保存在val中
int regmap_write(struct regmap *map, unsigned int reg, unsigned int val)；//將val寫入到reg中
int regmap_raw_write(struct regmap *map, unsigned int reg,
		     const void *val, size_t val_len)；//將val寫入到reg中，val長度爲val_len
int regmap_update_bits(struct regmap *map, unsigned int reg,
		       unsigned int mask, unsigned int val)//更新reg中指定的位

看下注冊過程：

regmap_init_i2c -> //regmap-i2c.c

regmap_init-> //多了兩個參數，最重要是第二個regmap_bus regmap_i2c，實現了I2C的讀寫，SPI同理

map->reg_read  = _regmap_bus_read; //綁定讀函數

map->reg_write = _regmap_bus_raw_write; //綁定寫函數

看下讀寫過程：

讀：

regmap_read ->

_regmap_read ->

map->reg_read -> //初始化時已經綁定_regmap_bus_read

_regmap_bus_read->

_regmap_raw_read ->

map->bus->read    //調用regmap-i2c.c中實現的regmap_i2c.read

寫：

regmap_write->
_regmap_write ->

map->reg_write  -> //初始化時已經綁定_regmap_bus_raw_write

_regmap_bus_raw_write->

_regmap_raw_write->

map->bus->write //調用regmap-i2c.c中實現的regmap_i2c.write

最後看看regmap-i2c.c吧

static int regmap_i2c_write(void *context, const void *data, size_t count)
{
	struct device *dev = context;
	struct i2c_client *i2c = to_i2c_client(dev);
	int ret;

	ret = i2c_master_send(i2c, data, count);
	if (ret == count)
		return 0;
	else if (ret < 0)
		return ret;
	else
		return -EIO;
}
static int regmap_i2c_read(void *context,
			   const void *reg, size_t reg_size,
			   void *val, size_t val_size)
{
	struct device *dev = context;
	struct i2c_client *i2c = to_i2c_client(dev);
	struct i2c_msg xfer[2];
	int ret;

	xfer[0].addr = i2c->addr;
	xfer[0].flags = 0;
	xfer[0].len = reg_size;
	xfer[0].buf = (void *)reg;
#ifdef CONFIG_I2C_ROCKCHIP_COMPAT
	xfer[0].scl_rate = 100*1000;
#endif

	xfer[1].addr = i2c->addr;
	xfer[1].flags = I2C_M_RD;
	xfer[1].len = val_size;
	xfer[1].buf = val;
#ifdef CONFIG_I2C_ROCKCHIP_COMPAT
	xfer[1].scl_rate = 100*1000;
#endif

	ret = i2c_transfer(i2c->adapter, xfer, 2);
	if (ret == 2)
		return 0;
	else if (ret < 0)
		return ret;
	else
		return -EIO;
}

熟悉吧，跟我們之前調用I2C的方法是一樣的。