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_masters2、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_add3、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_of4、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。