【简介】

LuckFox Pico Ultra 和 LuckFox Pico Ultra W 现在支持 RGB 屏幕，采用并行的 RGB LCD 接口。图像数据以 RGB666 格式传输，每个像素占用 6 位。目前的只适配分辨率有 720x720 和 480x480。为了帮助大家的理解工作原理，本节会从应用层到驱动层进行介绍，由于屏幕种类繁多，其它分辨率屏幕适配还需要自行研究。

刚到手可以使用开发板自带的程序测试屏幕，默认已经将测试程序打包到开发板上（/oem/usr/bin），如果想了解可执行程序的源码，在

/SDK目录//media/luckfox/examples  和  ./SDK目录/project/app/lvgl：

# luckfox_fb_test
The mem is :921600
The line_length is :1920
The xres is :480
The yres is :480
bits_per_pixel is :32

# luckfox_lvgl_test
fbdev_init

【MIPI DPI 接口】

【Rockchip 平台显示子系统（DSS）】

【FBDEV 介绍】

【DRM 介绍】

】DRM 与 framebuffer 的区别

【DRM 基本概念】

【DRM 框架介绍】

】Libdrm

】KMS

】GEM

】drm_panel

【驱动模块路径】

【设备树设置】

】Panel 设备节点

panel: panel {
                compatible = "simple-panel";
                backlight = <&backlight>;
               reset-gpios = <&gpio0 RK_PA1 GPIO_ACTIVE_LOW>;
               reset-delay-ms = <200>;
                status = "okay";

                bus-format = <MEDIA_BUS_FMT_RGB666_1X18>;
                width-mm = <85>;
                height-mm = <85>;

                display-timings {
                        native-mode = <&timing0>;
                        timing0: timing0 {
                                clock-frequency = <16500000>;
                                hactive = <480>;
                                vactive = <480>;
                                hback-porch = <43>;
                                hfront-porch = <8>;
                                vback-porch = <15>;
                                vfront-porch = <12>;
                                hsync-len = <4>;
                                vsync-len = <10>; //value range <2~22>
                                hsync-active = <0>;
                                vsync-active = <0>;
                                de-active = <0>;
                                pixelclk-active = <1>;
                        };
                };

                port {
                        panel_in_rgb: endpoint {
                                remote-endpoint = <&rgb_out_panel>;
                        };
                };
        };

】display_subsystem 设备节点

display_subsystem: display-subsystem {
                compatible = "rockchip,display-subsystem";
                ports = <&vop_out>;

】VOP 节点

vop: vop@ff990000 {
                compatible = "rockchip,rv1106-vop";
                reg = <0xff990000 0x200>;
                reg-names = "regs";
                rockchip,grf = <&grf>;
                interrupts = <GIC_SPI 89 IRQ_TYPE_LEVEL_HIGH>;
                clocks = <&cru ACLK_VOP>, <&cru DCLK_VOP>, <&cru HCLK_VOP>;
                clock-names = "aclk_vop", "dclk_vop", "hclk_vop";
                status = "disabled";

                vop_out: port {
                        #address-cells = <1>;
                        #size-cells = <0>;

                        vop_out_rgb: endpoint@0 {
                                reg = <0>;
                                remote-endpoint = <&rgb_in_vop>;
                        };  
                };
        };

】内核设置

cp ./arch/arm/configs/luckfox_rv1106_linux_defconfig .config
make ARCH=arm menuconfig

 Device Drivers --->
  Graphics support --->
     <*> Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)  ---> 
     <*>  DRM Support for Rockchip (DRM_ROCKCHIP [=y])
     [ ]   Support 3D cubic LUT
     [ ]   Rockchip DRM debug
     [ ]   Rockchip DRM direct show
     [*]   Rockchip VOP driver
     [ ]   Rockchip VOP2 driver
     [ ]   Rockchip specific extensions for Analogix DP driver
     [ ]   Rockchip cdn DP
     [ ]   Rockchip TVE support
     [ ]   Rockchip specific extensions for Synopsys DW HDMI
     [ ]   Rockchip specific extensions for Synopsys DW MIPI DSI
     [ ]   Rockchip specific extensions for Synopsys DW DPTX
     [ ]   Rockchip specific extensions for Innosilicon HDMI
     [ ]   Rockchip LVDS support
     [*]   Rockchip RGB support
     [ ]   Rockchip specific extensions for RK3066 HDMI
     [ ]   Rockchip Virtual connector driver for HDMI/DP/DSI
     [ ]   Rockchip virtual VOP drm driver< >   Synopsis Designware HDCP2 interface   

root@718974014fe6:/home/sysdrv/source/kernel/drivers/gpu/drm/rockchip# grep -rn "CONFIG_ROCKCHIP_RGB" ./
./Makefile:27:rockchipdrm-$(CONFIG_ROCKCHIP_RGB) += rockchip_rgb.o
./rockchip_drm_drv.c:2050:      ADD_ROCKCHIP_SUB_DRIVER(rockchip_rgb_driver, CONFIG_ROCKCHIP_RGB);
./rockchip_rgb.h:8:#ifdef CONFIG_ROCKCHIP_RGB

【DRM 驱动入口】

static struct platform_driver panel_simple_platform_driver = {
        .driver = {
                .name = "panel-simple",
                .of_match_table = platform_of_match,
        },
        .probe = panel_simple_platform_probe,
        .remove = panel_simple_platform_remove,
        .shutdown = panel_simple_platform_shutdown,
};

static int panel_simple_of_get_desc_data(struct device *dev,
                                         struct panel_desc *desc)
{
        struct device_node *np = dev->of_node;
        u32 bus_flags;
        const void *data;
        int len;
        int err;

        if (of_child_node_is_present(np, "display-timings")) {
                struct drm_display_mode *mode;

                mode = devm_kzalloc(dev, sizeof(*mode), GFP_KERNEL);
                if (!mode)
                        return -ENOMEM;

                if (!of_get_drm_display_mode(np, mode, &bus_flags,
                                             OF_USE_NATIVE_MODE)) {
                        desc->modes = mode;
                        desc->num_modes = 1;
                        desc->bus_flags = bus_flags;
                }

static int panel_simple_platform_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        const struct of_device_id *id;
        const struct panel_desc *desc;
        struct panel_desc *d;
        int err;

        id = of_match_node(platform_of_match, pdev->dev.of_node);
        if (!id)
                return -ENODEV;

        if (!id->data) {
                d = devm_kzalloc(dev, sizeof(*d), GFP_KERNEL);
                if (!d)
                        return -ENOMEM;

                err = panel_simple_of_get_desc_data(dev, d);
                if (err) {
                        dev_err(dev, "failed to get desc data: %d\n", err);
                        return err;
                }
        }

        desc = id->data ? id->data : d;

        return panel_simple_probe(&pdev->dev, desc);
}

void drm_panel_init(struct drm_panel *panel, struct device *dev,
                    const struct drm_panel_funcs *funcs, int connector_type)
{
        INIT_LIST_HEAD(&panel->list);
        panel->dev = dev;
        panel->funcs = funcs;
        panel->connector_type = connector_type;
}
EXPORT_SYMBOL(drm_panel_init);

/**
 * drm_panel_add - add a panel to the global registry
 * @panel: panel to add
 *
 * Add a panel to the global registry so that it can be looked up by display
 * drivers.
 */
void drm_panel_add(struct drm_panel *panel)
{
        mutex_lock(&panel_lock);
        list_add_tail(&panel->list, &panel_list);
        mutex_unlock(&panel_lock);
}
EXPORT_SYMBOL(drm_panel_add);

#define ADD_ROCKCHIP_SUB_DRIVER(drv, cond) { \
        if (IS_ENABLED(cond) && \
            !WARN_ON(num_rockchip_sub_drivers >= MAX_ROCKCHIP_SUB_DRIVERS)) \
                rockchip_sub_drivers[num_rockchip_sub_drivers++] = &drv; \
}

static int __init rockchip_drm_init(void)
{
        int ret;

        num_rockchip_sub_drivers = 0;
#if IS_ENABLED(CONFIG_DRM_ROCKCHIP_VVOP)
        ADD_ROCKCHIP_SUB_DRIVER(vvop_platform_driver, CONFIG_DRM_ROCKCHIP_VVOP);
#else
        ADD_ROCKCHIP_SUB_DRIVER(vop_platform_driver, CONFIG_ROCKCHIP_VOP);
        ...
        ADD_ROCKCHIP_SUB_DRIVER(rockchip_rgb_driver, CONFIG_ROCKCHIP_RGB);
        ...

#endif
        ret = platform_register_drivers(rockchip_sub_drivers,
                                        num_rockchip_sub_drivers);
        if (ret)
                return ret;

        ret = platform_driver_register(&rockchip_drm_platform_driver);
        if (ret)
                goto err_unreg_drivers;

        rockchip_gem_get_ddr_info();

        return 0;

err_unreg_drivers:
        platform_unregister_drivers(rockchip_sub_drivers,
                                    num_rockchip_sub_drivers);
        return ret;
}

static struct platform_driver rockchip_drm_platform_driver = {
        .probe = rockchip_drm_platform_probe,
        .remove = rockchip_drm_platform_remove,
        .shutdown = rockchip_drm_platform_shutdown,
        .driver = {
                .name = "rockchip-drm",       //此字段为device和driver匹配的最后一种方式
                .of_match_table = rockchip_drm_dt_ids,
                .pm = &rockchip_drm_pm_ops,
        },
};

static const struct of_device_id rockchip_drm_dt_ids[] = {
        { .compatible = "rockchip,display-subsystem", },
        { /* sentinel */ },
};

static int rockchip_drm_platform_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct component_match *match = NULL;
        int ret;

        ret = rockchip_drm_platform_of_probe(dev);
#if !IS_ENABLED(CONFIG_DRM_ROCKCHIP_VVOP)
        if (ret)
                return ret;
#endif

        match = rockchip_drm_match_add(dev);
        if (IS_ERR(match))
                return PTR_ERR(match);

        ret = dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(64));
        if (ret)
                goto err;

        ret = component_master_add_with_match(dev, &rockchip_drm_ops, match);
        if (ret < 0)
                goto err;

        return 0;
err:
        rockchip_drm_match_remove(dev);

        return ret;
}

总结：

• 设备树匹配：设备树中定义的面板节点通过设备树匹配机制与 panel-simple 驱动关联。内核启动时，rockchip-drm 平台驱动也会匹配设备树节点。驱动查找并解析设备树中的 ports 和 iommus 节点，以获取显示管道和内存管理单元的信息。
• 面板驱动初始化：panel_simple_platform_probe 函数读取设备树中的面板描述信息，并通过 panel_simple_probe 函数进行面板初始化和注册。在此过程中，调用 drm_panel_init 和 drm_panel_add 函数将面板初始化并注册到 DRM 框架中，使其成为 DRM 子系统的一部分，供其他 DRM 组件使用。
• 注册组件：rockchip-drm 使用 component_master_add_with_match 函数将其注册到组件框架中。通过设置 rockchip_drm_ops，定义了 bind 和 unbind 操作，这些操作将在组件初始化和注销时调用。
• 添加子组件：各个子组件（例如 VOP、HDMI、MIPI DSI 等）使用 component_add 函数添加到组件框架中。每个子组件都有对应的 component_ops 结构体，定义其自身的 bind 和 unbind 操作。
• 绑定组件：当 master 组件（即 rockchip-drm）匹配到所有子组件后，会调用其 bind 回调函数。在 bind 回调函数中，执行各个子组件的初始化和配置。
• 注册到 DRM 核心：rockchip-drm 驱动在内核模块加载时通过 drm_dev_register 函数注册 DRM 设备。在此过程中，drm_dev_register 会调用 drm_minor_register 注册字符设备。drm_minor_register 函数负责创建字符设备并添加到 /dev/dri 目录下，最终创建设备节点，如 /dev/dri/card0。

想了解更多具体内容，需自己进入源码目录（drivers/gpu/drm）阅读理解。