FBDEV
Framebuffer device
社区参与度不高，基本转移到了DRM。
DRM/KMS
Direct Rendering Manager / KernelMode Setting
主流的图形显示方法，社区参与度高，支持图形系统精细化操作，基本形成了一套图显系统开发的生态标准。
V4L2
Video For Linux 2
主要用于视频捕获的应用场景，并且需要特定输出设备，对复杂图显控制器的支持不佳
图片来源于网络
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图片来源于网络
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##显存Framebuffer
申请的一块用于存储显示数据的内存区域，主要包括：
1）内存区域大小范围
2）内存中待显示数据的帧格式
3）内存中有效的区域，该部分是待显示数据
其实现方法主要有3种：
1）基于CMA的
drivers/gpu/drm/drm_fb_cma_helper.c
2）基于Scatter Gather
drivers/gpu/drm/tegra/
3）基于IOMMU
drivers/gpu/drm/exynos/exynos_drm_iommu.c
显存区域定义
帧格式定义
1/* 24 bpp RGB */
2#define DRM_FORMAT_RGB888 fourcc_code('R', 'G', '2', '4')
3#define DRM_FORMAT_BGR888 fourcc_code('B', 'G', '2', '4')
4
5/* 32 bpp RGB */
6#define DRM_FORMAT_XRGB8888 fourcc_code('X', 'R', '2', '4')
7#define DRM_FORMAT_XBGR8888 fourcc_code('X', 'B', '2', '4')
8#define DRM_FORMAT_RGBX8888 fourcc_code('R', 'X', '2', '4')
9#define DRM_FORMAT_BGRX8888 fourcc_code('B', 'X', '2', '4')
创建FRAME BUFFER
##CRTC
CRTC funcs
1static const struct drm_crtc_funcs ade_crtc_funcs = {
2 .destroy = drm_crtc_cleanup,
3 .set_config = drm_atomic_helper_set_config,
4 .page_flip = drm_atomic_helper_page_flip,
5 .reset = drm_atomic_helper_crtc_reset,
6 .atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
7 .atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
8 .enable_vblank = ade_crtc_enable_vblank,
9 .disable_vblank = ade_crtc_disable_vblank,
10};
CRTC helper funcs
1static const struct drm_crtc_helper_funcs ade_crtc_helper_funcs = {
2 .mode_fixup = ade_crtc_mode_fixup,
3 .mode_set_nofb = ade_crtc_mode_set_nofb,
4 .atomic_begin = ade_crtc_atomic_begin,
5 .atomic_flush = ade_crtc_atomic_flush,
6 .atomic_enable = ade_crtc_atomic_enable,
7 .atomic_disable = ade_crtc_atomic_disable,
8};
##PLANE
图片来源于网络
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PLANE funcs
1static struct drm_plane_funcs ade_plane_funcs = {
2 .update_plane = drm_atomic_helper_update_plane,
3 .disable_plane = drm_atomic_helper_disable_plane,
4 .destroy = drm_plane_cleanup,
5 .reset = drm_atomic_helper_plane_reset,
6 .atomic_duplicate_state = drm_atomic_helper_plane_duplicate_state,
7 .atomic_destroy_state = drm_atomic_helper_plane_destroy_state,
8};
PLANE helper funcs
1static const struct drm_plane_helper_funcs ade_plane_helper_funcs = {
2 .atomic_check = ade_plane_atomic_check,
3 .atomic_update = ade_plane_atomic_update,
4 .atomic_disable = ade_plane_atomic_disable,
5};
##ENCODER/CONNECTOR
图片来源于网络
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ENCODER/helper funcs
1static const struct drm_encoder_helper_funcs dw_encoder_helper_funcs = {
2 .atomic_check = dsi_encoder_atomic_check,
3 .mode_valid = dsi_encoder_mode_valid,
4 .mode_set = dsi_encoder_mode_set,
5 .enable = dsi_encoder_enable,
6 .disable = dsi_encoder_disable
7};
8
9static const struct drm_encoder_funcs dw_encoder_funcs = {
10 .destroy = drm_encoder_cleanup,
11};
CONNECTOR/helper funcs
1static const struct drm_connector_helper_funcs
2panel_bridge_connector_helper_funcs = {
3 .get_modes = panel_bridge_connector_get_modes,
4};
5
6static const struct drm_connector_funcs panel_bridge_connector_funcs = {
7 .reset = drm_atomic_helper_connector_reset,
8 .fill_modes = drm_helper_probe_single_connector_modes,
9 .destroy = drm_connector_cleanup,
10 .atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
11 .atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
12};
##ioctl注册
master是设备树中的“超级设备（superdevice）”，负责管理该超级设备下的普通设备。component是由master管理的普通设备，要先初始化。
#初始化分为两部分
component即普通设备，执行probe使用component_add函数注册自己到component框架中。
##Master初始化
1static int kirin_drm_platform_probe(struct platform_device *pdev)
2{
3 struct device *dev = &pdev->dev;
4 struct device_node *np = dev->of_node;
5 struct component_match *match = NULL;
6 struct device_node *remote;
7
8 remote = of_graph_get_remote_node(np, , );
9 if (!remote)
10 return -ENODEV;
11
12 drm_of_component_match_add(dev, &match, compare_of, remote);
13 of_node_put(remote);
14
15 return component_master_add_with_match(dev, &kirin_drm_ops, match);
16}
##Component初始化
1static int dsi_probe(struct platform_device *pdev)
2{
3 struct dsi_data *data;
4 struct dw_dsi *dsi;
5 struct dsi_hw_ctx *ctx;
6 int ret;
7
8 data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
9 if (!data) {
10 DRM_ERROR("failed to allocate dsi data.\n");
11 return -ENOMEM;
12 }
13 dsi = &data->dsi;
14 ctx = &data->ctx;
15 dsi->ctx = ctx;
16
17 ret = dsi_parse_dt(pdev, dsi);
18 if (ret)
19 return ret;
20
21 platform_set_drvdata(pdev, data);
22
23 return component_add(&pdev->dev, &dsi_ops);
24}
##设备树定义
1ade: ade@f4100000 {
2 compatible = "hisilicon,hi6220-ade";
3 reg = <0x0 0xf4100000 0x0 0x7800>;
4 reg-names = "ade_base";
5 hisilicon,noc-syscon = <&medianoc_ade>;
6 resets = <&media_ctrl MEDIA_ADE>;
7 interrupts = < 115 4>; /* ldi interrupt */
8
9 clocks = <&media_ctrl HI6220_ADE_CORE>,
10 <&media_ctrl HI6220_CODEC_JPEG>,
11 <&media_ctrl HI6220_ADE_PIX_SRC>;
12 /*clock name*/
13 clock-names = "clk_ade_core",
14 "clk_codec_jpeg",
15 "clk_ade_pix";
16
17 assigned-clocks = <&media_ctrl HI6220_ADE_CORE>,
18 <&media_ctrl HI6220_CODEC_JPEG>;
19 assigned-clock-rates = <360000000>, <288000000>;
20 dma-coherent;
21 status = "disabled";
22
23 port {
24 ade_out: endpoint {
25 remote-endpoint = <&dsi_in>;
26 };
27 };
28};
29
30dsi: dsi@f4107800 {
31 compatible = "hisilicon,hi6220-dsi";
32 reg = <0x0 0xf4107800 0x0 0x100>;
33 clocks = <&media_ctrl HI6220_DSI_PCLK>;
34 clock-names = "pclk";
35 status = "disabled";
36
37 ports {
38 #address-cells = <1>;
39 #size-cells = <>;
40
41 /* 0 for input port */
42 port@ {
43 reg = <>;
44 dsi_in: endpoint {
45 remote-endpoint = <&ade_out>;
46 };
47 };
48 };
49};
填充不同的数据格式显示结果如下：
- EOF -
以上文章来源于Linux与SoC ，作者spy_os
