这篇文章主要介绍“Linux DRM的component框架有什么作用”，在日常操作中，相信很多人在Linux DRM的component框架有什么作用问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”Linux DRM的component框架有什么作用”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
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一、component介绍
Linux内核component代码实现文件：drivers/base/component.c。
使用git log -p component.c命令，可以查看该文件的第一次提交记录。
commit 2a41e6070dd7ef539d0f3b1652b4839d04378e11Author: Russell King Date: Fri Jan 10 23:23:37 2014 +0000 drivers/base: provide an infrastructure for componentised subsystems Subsystems such as ALSA, DRM and others require a single card-level device structure to represent a subsystem. However, firmware tends to describe the individual devices and the connections between them. Therefore, we need a way to gather up the individual component devices together, and indicate when we have all the component devices. We do this in DT by providing a "superdevice" node which specifies the components, eg: imx-drm { compatible = "fsl,drm"; crtcs = <&ipu1>; connectors = <&hdmi>; }; The superdevice is declared into the component support, along with the subcomponents. The superdevice receives callbacks to locate the subcomponents, and identify when all components are present. At this point, we bind the superdevice, which causes the appropriate subsystem to be initialised in the conventional way. When any of the components or superdevice are removed from the system, we unbind the superdevice, thereby taking the subsystem down.
Linux内核引入component框架的目的：
在DRM、ALSA等子系统中，通过超级设备（superdevice）管理多个组件（component）加载顺序，保证所有组件都可正常使用。
二、超级设备
1.超级设备定义
超级设备也可称为master，一般指某个子系统（如：display-subsystem）。定义文件：rk3399.dtsi，内容如下：
display_subsystem: display-subsystem { compatible = "rockchip,display-subsystem"; ports = <&vopl_out>, <&vopb_out>; clocks = <&cru PLL_VPLL>, <&cru PLL_CPLL>; clock-names = "hdmi-tmds-pll", "default-vop-pll"; devfreq = <&dmc>; status = "disabled"; };2.超级设备加载
超级设备通过component_master_add_with_match()函数进行match注册，实现文件：rockchip_drm_drv.c，内容如下：
static int rockchip_drm_platform_probe(struct platform_device *pdev){ ... /* * Bind the crtc ports first, so that * drm_of_find_possible_crtcs called from encoder .bind callbacks * works as expected. */ for (i = 0;; i++) { ... port = of_parse_phandle(np, "ports", i); ... component_match_add(dev, &match, compare_of, port->parent); ## 1. Bind CRTC of_node_put(port); } ... /* * For each bound crtc, bind the encoders attached to its * remote endpoint. */ for (i = 0;; i++) { port = of_parse_phandle(np, "ports", i); ... rockchip_add_endpoints(dev, &match, port); ## 2. add endpoints for each port of_node_put(port); } ... return component_master_add_with_match(dev, &rockchip_drm_ops, match);}三、component设备
1.component设备定义
component设备用来表示vop和各显示接口（如：HDMI、MIPI等），定义文件：rk3399.dtsi，内容如下：
vopl_out: port { #address-cells = <1>; #size-cells = <0>; vopl_out_dsi: endpoint@0 { reg = <0>; remote-endpoint = <&dsi_in_vopl>; }; ... vopl_out_hdmi: endpoint@2 { reg = <2>; remote-endpoint = <&hdmi_in_vopl>; }; ... }; vopb_out: port { #address-cells = <1>; #size-cells = <0>; ... vopb_out_dsi: endpoint@1 { reg = <1>; remote-endpoint = <&dsi_in_vopb>; }; vopb_out_hdmi: endpoint@2 { reg = <2>; remote-endpoint = <&hdmi_in_vopb>; }; ... };2.component设备加载
component设备通过component_add（）函数进行加载。
vop实现文件rockchip_vop_reg.c，代码如下：
static int vop_probe(struct platform_device *pdev){ ... return component_add(dev, &vop_component_ops);}HDMI接口实现文件dw_hdmi-rockchip.c，代码如下：
static int dw_hdmi_rockchip_probe(struct platform_device *pdev){ ... return component_add(&pdev->dev, &dw_hdmi_rockchip_ops);}其它接口暂不介绍。
PS：
VOP（Video Output Processor）是Rockchip系列SoC的显示控制器。RK3399显示特性如下：
1、Dual VOP: one supports 4096x2160 with AFBC supported；The other supports 2560x16002、Dual channel MIPI-DSI (4 lanes per channel)3、eDP 1.3 (4 lanes with 10.8Gbps) to support display, with PSR4、HDMI 2.0 for 4K 60Hz with HDCP 1.4/2.25、DisplayPort 1.2 (4 lanes, up to 4K 60Hz)6、Supports Rec.2020 and conversion to Rec.709
注：本文代码基于RockPI 4A Debian系统Linux 4.4内核。
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