本文基于RockPI 4A DRM框架介绍Linux 4.4内核component组件bind过程。

一、加载顺序

RockPI 4A单板DRM模块
drivers/gpu/drm/rockchip/Makefile内容如下：

rockchipdrm-y := rockchip_drm_drv.o rockchip_drm_fb.o \
                rockchip_drm_gem.o rockchip_drm_vop.o
...
obj-$(CONFIG_ROCKCHIP_DW_HDMI) += dw_hdmi-rockchip.o
...
obj-$(CONFIG_DRM_ROCKCHIP) += rockchip_vop_reg.o rockchipdrm.o

注：DRM框架目前只关注HDMI显示，其它连接方式处理相同，暂不讨论。

根据Makefile内容，确定DRM模块的编译顺序，具体如下：

  CC      drivers/gpu/drm/rockchip/dw_hdmi-rockchip.o
  ...
  CC      drivers/gpu/drm/rockchip/rockchip_vop_reg.o
  CC      drivers/gpu/drm/rockchip/rockchip_drm_drv.o
  ...
  LD      drivers/gpu/drm/rockchip/rockchipdrm.o
  LD      drivers/gpu/drm/rockchip/built-in.o

即：

dw_hdmi-rockchip.c（encoder component设备）->

rockchip_vop_reg.c（crtc component设备）->

rockchip_drm_drv.c（core master设备）

编译和链接的过程决定了这三个模块的component加载顺序：encoder component->crtc component ->core master。

二、component设备

DRM模块encoder和crtc驱动在各自模块的探测函数probe()中使用component_add()函数添加component设备。

crtc实现文件：
drivers/gpu/drm/rockchip/rockchip_drm_vop.c、rockchip_vop_reg.c；

encoder实现文件：
drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c。

例：

文件:
drivers/gpu/drm/rockchip/rockchip_vop_reg.c

## 初始化bind和unbind的实现函数
const struct component_ops vop_component_ops = {
    .bind = vop_bind,
    .unbind = vop_unbind,
};

## 添加crtc component设备
static int vop_probe(struct platform_device *pdev)
{
    ...
    return component_add(dev, &vop_component_ops);
}

文件：drivers/base/omponent.c，component_add()定义如下：

int component_add(struct device *dev, const struct component_ops *ops)
{
    struct component *component;
    ...
    
    ## 1.初始化component结构体
    component = kzalloc(sizeof(*component), GFP_KERNEL);
    ...
    component->ops = ops;
    component->dev = dev;
    ...
    
    ## 2.将component中node添加到component_list链表中
    list_add_tail(&component->node, &component_list);

    ## 3.尝试匹配master设备
    ret = try_to_bring_up_masters(component);
    ...
}

static int try_to_bring_up_masters(struct component *component)
{
    struct master *m;
    ...
    ## 搜索masters链表，此时master设备尚未注册，不会执行try_to_bring_up_master()
    list_for_each_entry(m, &masters, node) {
        ret = try_to_bring_up_master(m, component);
        if (ret != 0)
            break;
    }
    ...
}

上面函数中涉及的定义如下：

## master设备结构体定义
struct master {
    struct list_head node;
    struct list_head components;
    bool bound;

    const struct component_master_ops *ops;
    struct device *dev;
    struct component_match *match;
};

## component设备结构体定义
struct component {
    struct list_head node;
    struct list_head master_node;
    struct master *master;
    bool bound;

    const struct component_ops *ops;
    struct device *dev;
};

## componet设备链表和master设备链表
static LIST_HEAD(component_list);
static LIST_HEAD(masters);

注：

在DRM模块中，先加载component设备，不会运行到try_to_bring_up_master()函数。

在其它模块中，component和master设备的加载顺序不一定相同，上面函数的执行流程可能会有差异。

三、master设备

添加master设备包括两步：

1）、component_match_add() ：添加待匹配的component设备。

2）、
component_master_add_with_match()：初始化master设备并匹配component设备。若匹配成功，则执行master设备的bind函数。

例：

文件：
drivers/gpu/drm/rockchip/rockchip_drm_drv.c，实现如下：

static int rockchip_drm_platform_probe(struct platform_device *pdev)
{
    struct component_match *match = NULL;
    ...
    for (i = 0;; i++) {
        ...
        ## 1. 添加待匹配的component设备，即添加crtc
        component_match_add(dev, &match, compare_of, port->parent); 
        ...
    }
    ...
    for (i = 0;; i++) {
        ...
        ## 2. 添加待绑定的component设备，即添加每个crtc的encoder
        rockchip_add_endpoints(dev, &match, port);
        ...
    }
    ...
    ## 3.添加master设备并匹配component设备
    ## 由于component设备已经添加完成，会在完成componet设备匹配后调用master设备的bind函数
    return component_master_add_with_match(dev, &rockchip_drm_ops, match);
}

涉及的结构体定义如下：

struct component_match {
    size_t alloc;
    size_t num;
    struct {
        void *data;
        int (*fn)(struct device *, void *);
    } compare[0];
};

## master设备bind和unbind定义
static const struct component_master_ops rockchip_drm_ops = {
    .bind = rockchip_drm_bind,
    .unbind = rockchip_drm_unbind,
};

1、component_match_add()函数

函数功能：添加待匹配的component组件。

函数实现：

void component_match_add(struct device *dev, struct component_match **matchptr,
    int (*compare)(struct device *, void *), void *compare_data)
{
    struct component_match *match = *matchptr;
    ...
    ## 1.添加第一个待匹配的组件时，match为空，new_size大小为15
    if (!match || match->num == match->alloc) {
        size_t new_size = match ? match->alloc + 16 : 15;
        ## 申请16个(对应match->compare[0] ~ match->compare[15])component_match结构体大小的内存
        ## 在component_master_add_with_match()函数中，会根据实际component个数，重新申请内存
        match = component_match_realloc(dev, match, new_size);
        *matchptr = match;
        ...
    }

    ## 2.初始化match
    match->compare[match->num].fn = compare;
    match->compare[match->num].data = compare_data;
    match->num++;
}

2、
component_master_add_with_match()函数

函数功能：初始化master设备，在匹配component设备成功后，调用master设备的bind函数。

函数实现：

int component_master_add_with_match(struct device *dev,
    const struct component_master_ops *ops,
    struct component_match *match)
{
    struct master *master;
    ...
    
    ## 1.若存在match，则按照实际大小重新申请内存
    if (match) {
        /* Reallocate the match array for its true size */
        match = component_match_realloc(dev, match, match->num);
        if (IS_ERR(match))
            return PTR_ERR(match);
    }

    ## 2.初始化master设备
    master = kzalloc(sizeof(*master), GFP_KERNEL);
    ...
    master->dev = dev;
    master->ops = ops;
    master->match = match;
    INIT_LIST_HEAD(&master->components);

    ## 3.将master设备的node添加到masters列表
    list_add(&master->node, &masters);

    ## 4.查找component设备，若匹配成功，则执行master设备的bind函数。
    ret = try_to_bring_up_master(master, NULL);
    ...
}

2.1、try_to_bring_up_master()函数

函数功能：查找component设备，若匹配成功，则执行master设备的bind函数。

函数实现：

static int try_to_bring_up_master(struct master *master,
    struct component *component)
{
    ...
    ## 1.查找component设备
    if (find_components(master)) {
        ...
    }

    ## 2.查找到所有的component设备后，调用master设备的bind函数，即rockchip_drm_bind()
    ret = master->ops->bind(master->dev);
    ...
}

2.2、find_components()函数

函数功能：逐个扫描component设备并和master设备匹配。若匹配成功，则添加到master设备。

函数实现：

static int find_components(struct master *master)
{
    struct component_match *match = master->match;
    ...
    ## 逐个扫描component设备并和master设备匹配。成功，则添加到master设备
    for (i = 0; i < match->num; i++) {
        ret = component_master_add_child(master,
                         match->compare[i].fn,
                         match->compare[i].data);
        ...
    }
    ...
}

2.3、
component_master_add_child()

函数功能：在component_list链表中扫描component设备并匹配。若匹配成功，则添加到master设备中。

函数实现：

int component_master_add_child(struct master *master,
    int (*compare)(struct device *, void *), void *compare_data)
{
    ...
    ## 1.在component_list链表中扫描component设备
    list_for_each_entry(c, &component_list, node) {
        if (c->master && c->master != master)
            continue;

        ## 2.通过compare()函数匹配component设备。若匹配，则添加到master设备中
        if (compare(c->dev, compare_data)) {
            if (!c->master)
                component_attach_master(master, c);
            ...
        }
    }
    ...
}

注：component设备的相关函数都在drivers/base/omponent.c里实现。

四、bind过程

在try_to_bring_up_master()函数中，最终会调用master设备的bind函数，即rockchip_drm_bind()，在该函数里会执行component_bind_all()函数，调用各component设备的bind函数。

int component_bind_all(struct device *master_dev, void *data)
{
    struct master *master;
    ...
    list_for_each_entry(c, &master->components, master_node) {
        ret = component_bind(c, master, data);
        ...
    }
    ...
}

在代码里添加了部分log，单板启动后，打印如下：

1、添加component设备，此时没有添加master设备，无法匹配

[    2.259259] [drm] Initialized drm 1.1.0 20060810
## 1.添加encoder component设备
[    2.260622] --- dw_hdmi_rockchip_probe
[    2.260989] dwhdmi-rockchip ff940000.hdmi: adding component (ops 0xffffff8008d51f80)
[    2.261672]  === try_to_bring_up_masters

## 2.添加crtc component设备
[    2.266464]  ---- vop_probe
[    2.266819] rockchip-vop ff8f0000.vop: adding component (ops 0xffffff8008d5b808)
[    2.267468]  === try_to_bring_up_masters

## 3.添加crtc component设备
[    2.268093]  ---- vop_probe
[    2.268360] rockchip-vop ff900000.vop: adding component (ops 0xffffff8008d5b808)
[    2.269007]  === try_to_bring_up_masters

2、在master设备中，添加待匹配的component设备，即：crtc和encoder

[    2.269867] [drm] Rockchip DRM driver version: v1.0.1

## 1.添加待匹配的vopb对应crtc，第一次添加申请16个component_match结构体大小的内存
[    2.270348] --- rockchip_drm_platform_probe crtc port is port, type is <NULL>, full_name is /vop@ff900000/port
[    2.271277]  === component_match_add
[    2.271613]  === component_match_realloc num 15

## 2.添加待匹配的vopl对应crtc
[    2.272040] --- rockchip_drm_platform_probe crtc port is port, type is <NULL>, full_name is /vop@ff8f0000/port
[    2.272934]  === component_match_add

## 3.添加待匹配的vopb对应的encoder
[    2.273268]  --- rockchip_drm_platform_probe encoder port is port, type is <NULL>, full_name is /vop@ff900000/port
[    2.274230]  --- endpoint port is hdmi, type is <NULL>, full_name is /hdmi@ff940000
[    2.274918]  === component_match_add

## 4.添加待匹配的vopl对应的encoder,3和4的component相同
[    2.275284]  --- rockchip_drm_platform_probe encoder port is port, type is <NULL>, full_name is /vop@ff8f0000/port
[    2.276242]  --- endpoint port is hdmi, type is <NULL>, full_name is /hdmi@ff940000
[    2.276912]  === component_match_add

3、添加master设备，并匹配

## 1.按照实际component个数申请内存
[    2.277261]  === component_match_realloc match num 4

## 2.开始扫描，第一个匹配
[    2.277705]  === try_to_bring_up_master
[    2.278056]  === find_components match->num 0
[    2.278441]  --- compare_of
[    2.278725]  --- compare_of
[    2.278725]   --- compare_of
[    2.279287]  --- compare_of
[    2.279695]  === component_attach_master

## 3.第二个匹配
[    2.280045]  === find_components match->num 1
[    2.280429]  --- compare_of
[    2.280697]  --- compare_of
[    2.280697]   --- compare_of
[    2.281257]  === component_attach_master

## 3.第三个匹配
[    2.281631]  === find_components match->num 2
[    2.282014]  --- compare_of
[    2.282282]  === component_attach_master

## 4.第四个不用匹配
[    2.282669]  === find_components match->num 3
[    2.283053]  --- compare_of

4、执行master和各component设备bind

## 1.master bind
[    2.283322]  try_to_bring_up_master bind
[    2.284733]  --- rockchip_drm_bind

## 2. component(vopb) bind
[    2.285039]  === component_bind_all component_bind
[    2.285478] rockchip-drm display-subsystem: binding ff900000.vop (ops 0xffffff8008d5b808)
[    2.286195]  --- drm vop bind
[    2.286539] rockchip-vop ff900000.vop: missing rockchip,grf property
[    2.287524] rockchip-drm display-subsystem: bound ff900000.vop (ops 0xffffff8008d5b808)

## 3. component(vopl) bind
[    2.288229]  === component_bind_all component_bind
[    2.288667] rockchip-drm display-subsystem: binding ff8f0000.vop (ops 0xffffff8008d5b808)
[    2.289382]  --- drm vop bind
[    2.289700] rockchip-vop ff8f0000.vop: missing rockchip,grf property
[    2.290522] rockchip-drm display-subsystem: bound ff8f0000.vop (ops 0xffffff8008d5b808)

## 4. component(hdmi encoder) bind
[    2.291245]  === component_bind_all component_bind
[    2.291683] rockchip-drm display-subsystem: binding ff940000.hdmi (ops 0xffffff8008d51f80)
[    2.292411]  ---- dw_hdmi_rockchip_bind

注：本文仅在简书、OSCHINA和今日头条发布过，转载请标注原作者和链接。