uboot - 驱动开发 - 驱动模型

说明

• 类似于linux，为了规范、统一驱动适配和驱动接口调用，uboot定义了一套驱动模型(Driver Model)，简称DM。
• 本文基于：u-boot-2021.10。

优点

1. 为同一类ip的驱动定义了统一的操作接口，DM在软件层面做了一定的抽象。
2. 分层设计，将上层使用、设备以及驱动实现区分开来，降低了耦合性。

核心概念/数据结构

• DM模型抽象出了以下四个概念/数据结构。

1. uclass
2. uclass_driver
3. udevice
4. driver

uclass

• uclass（uboot class）是同一类外设（I2C、GPIO等）总的组织结构体，定义如下：

// file：include/dm/uclass.h
/**
 * struct uclass - a U-Boot drive class, collecting together similar drivers
 *
 * A uclass provides an interface to a particular function, which is
 * implemented by one or more drivers. Every driver belongs to a uclass even
 * if it is the only driver in that uclass. An example uclass is GPIO, which
 * provides the ability to change read inputs, set and clear outputs, etc.
 * There may be drivers for on-chip SoC GPIO banks, I2C GPIO expanders and
 * PMIC IO lines, all made available in a unified way through the uclass.
 *
 * @priv_: Private data for this uclass (do not access outside driver model)
 * @uc_drv: The driver for the uclass itself, not to be confused with a
 * 'struct driver'
 * @dev_head: List of devices in this uclass (devices are attached to their
 * uclass when their bind method is called)
 * @sibling_node: Next uclass in the linked list of uclasses
 */
struct uclass {
    void *priv_;
    struct uclass_driver *uc_drv;
    struct list_head dev_head;
    struct list_head sibling_node;
};

• uclass 包含

1. uc_drv: uclass driver。
2. dev_head: udevice list(设备列表)。
3. sibling_node: 链表的