i2c_add_adapter

最新推荐文章于 2024-04-23 22:15:20 发布

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最新推荐文章于 2024-04-23 22:15:20 发布 · 1k 阅读

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这篇博客详细介绍了在Linux驱动中，如何通过i2c_add_adapter和i2c_add_numbered_adapter函数动态和静态地添加I2C适配器。这两个函数主要负责将I2C适配器注册到系统并创建相应的/sys/class/i2c-adapter目录。动态添加的适配器编号是动态申请的，而静态添加的编号在添加前已预先分配。注册过程包括将适配器添加到管理链表、创建设备表示以及扫描并附加客户端设备。

drivers/i2c/algos/i2c-algo-bit.c 中有两个函数都是用来添加adapter的,

一个是动态添加i2c_add_adapter()，

一个是静态添加i2c_add_numbered_adapter(), numbered就是已经定好了adapter id号了的意思。

int i2c_bit_add_bus(struct i2c_adapter *adap)
{
        int err;

        err = i2c_bit_prepare_bus(adap);
        if (err)
                return err;

        return i2c_add_adapter(adap);
}
EXPORT_SYMBOL(i2c_bit_add_bus);

int i2c_bit_add_numbered_bus(struct i2c_adapter *adap)
{
        int err;

        err = i2c_bit_prepare_bus(adap);
        if (err)
                return err;

        return i2c_add_numbered_adapter(adap);
}
EXPORT_SYMBOL(i2c_bit_add_numbered_bus);

i2c_add_adapter() 的工作就是向系统，向/sys 注册i2c_adapter，以备后面的i2c操作。

/**
 * i2c_add_adapter - declare i2c adapter, use dynamic bus number
 * @adapter: the adapter to add
 *
 * This routine is used to declare an I2C adapter when its bus number
 * doesn't matter.  Examples: for I2C adapters dynamically added by
 * USB links or PCI plugin cards.
 *
 * When this returns zero, a new bus number was allocated and stored
 * in adap->nr, and the specified adapter became available for clients.
 * Otherwise, a negative errno value is returned.
 */
int i2c_add_adapter(struct i2c_adapter *adapter)
{
        int     id, res = 0;

retry:
        if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) == 0)
                return -ENOMEM;

        mutex_lock(&core_lists);
        /* "above" here means "above or equal to", sigh */
        res = idr_get_new_above(&i2c_adapter_idr, adapter,
                                __i2c_first_dynamic_bus_num, &id);
        mutex_unlock(&core_lists);

        if (res < 0) {
                if (res == -EAGAIN)
                        goto retry;
                return res;
        }

        adapter->nr = id;
        return i2c_register_adapter(adapter);
}
EXPORT_SYMBOL(i2c_add_adapter);

idr 机制是linux系统中的一种数据结构，一种方便检索的机制，idr的要完成的任务是给要管理的对象分配一个数字，可以通过这个数字找到要管理的对象。

网上一堆介绍idr的。

i2c_add_numbered_adapter() 也差不多，不过他的adapter->nr 不是动态申请的，是原先就静态分配好的。

/**
 * i2c_add_numbered_adapter - declare i2c adapter, use static bus number
 * @adap: the adapter to register (with adap->nr initialized)
 *
 * This routine is used to declare an I2C adapter when its bus number
 * matters.  Example: for I2C adapters from system-on-chip CPUs, or
 * otherwise built in to the system's mainboard, and where i2c_board_info
 * is used to properly configure I2C devices.
 *
 * If no devices have pre-been declared for this bus, then be sure to
 * register the adapter before any dynamically allocated ones.  Otherwise
 * the required bus ID may not be available.
 *
 * When this returns zero, the specified adapter became available for
 * clients using the bus number provided in adap->nr.  Also, the table
 * of I2C devices pre-declared using i2c_register_board_info() is scanned,
 * and the appropriate driver model device nodes are created.  Otherwise, a
 * negative errno value is returned.
 */
int i2c_add_numbered_adapter(struct i2c_adapter *adap)
{
        int     id;
        int     status;

        if (adap->nr & ~MAX_ID_MASK)
                return -EINVAL;

retry:
        if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) == 0)
                return