如何在Yocto Linux设备树中添加双LCD面板并通过Barebox切换启用

问题根源分析 #

1. Duplicate label 'panel_in'错误：设备树中每个节点的label必须唯一，两个panel-lcd节点的endpoint共用panel_in标签，违反DTS语法规则。
2. Cannot connect bridge: -19错误：错误码-19对应ENODEV，内核无法找到LCD控制器（lcdif）与启用面板的有效连接路径。修改label后，lcdif的remote-endpoint仍指向固定旧标签，切换面板时未同步更新该指向，导致连接失败。

解决方案步骤 #

1. 修改设备树，给每个面板的Endpoint分配唯一Label #

修改DTSI文件，为两个面板的endpoint设置唯一标识，同时让lcdif默认指向其中一个面板（后续由Barebox动态修改）：

/ {
    panel-lcd-tn {
        compatible = "powertip,ph320240t023_iha";
        backlight = <&backlight_peb>;
        status = "disabled";

        port {
            panel_in_tn: endpoint {
                remote-endpoint = <&display_out>;
            };
        };
    };

    panel-lcd-ips {
        compatible = "powertip,ph320240t028_zha";
        backlight = <&backlight_peb>;
        status = "disabled";

        port {
            panel_in_ips: endpoint {
                remote-endpoint = <&display_out>;
            };
        };
    };
...
};

&lcdif {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_lcdif_dat>;
    status = "okay"; // 提前启用控制器，避免重复修改

    port {
        display_out: endpoint {
            remote-endpoint = <&panel_in_tn>; // 默认指向TN面板
        };
    };
};

2. 在Barebox中添加动态切换逻辑 #

切换面板时，不仅要修改面板的status，还要同步更新lcdif的remote-endpoint指向当前启用的面板。以下是两种实现方式：

方式一：C语言Fixup函数

#include <of.h>

static int panel_fixup(struct device_node *root, void *ctx)
{
    struct device_node *tn_panel, *ips_panel, *lcdif, *lcdif_ep;
    const char *panel_type = ctx;

    // 获取目标节点
    tn_panel = of_find_node_by_path(root, "/panel-lcd-tn");
    ips_panel = of_find_node_by_path(root, "/panel-lcd-ips");
    lcdif = of_find_node_by_path(root, "/soc/aips-bus@02100000/lcdif@021c8000");
    if (!tn_panel || !ips_panel || !lcdif)
        return -EINVAL;

    lcdif_ep = of_get_child_by_name(lcdif, "port");
    if (lcdif_ep)
        lcdif_ep = of_get_child_by_name(lcdif_ep, "endpoint");

    // 根据选择切换面板并更新连接
    if (!strcmp(panel_type, "tn")) {
        of_fixup_status(tn_panel, "okay");
        of_fixup_status(ips_panel, "disabled");
        if (lcdif_ep)
            of_property_set_string(lcdif_ep, "remote-endpoint", "panel_in_tn");
    } else if (!strcmp(panel_type, "ips")) {
        of_fixup_status(tn_panel, "disabled");
        of_fixup_status(ips_panel, "okay");
        if (lcdif_ep)
            of_property_set_string(lcdif_ep, "remote-endpoint", "panel_in_ips");
    }

    return 0;
}

BAREBOX_FIXUP(panel_fixup, "panel-fixup", panel_fixup);

方式二：Barebox启动脚本命令行修改

# 切换到TN面板
fdt set /panel-lcd-tn status okay
fdt set /panel-lcd-ips status disabled
fdt set /soc/aips-bus@02100000/lcdif@021c8000/port/endpoint remote-endpoint <&panel_in_tn>

# 切换到IPS面板
fdt set /panel-lcd-tn status disabled
fdt set /panel-lcd-ips status okay
fdt set /soc/aips-bus@02100000/lcdif@021c8000/port/endpoint remote-endpoint <&panel_in_ips>

3. 验证与调试 #

• 编译修改后的设备树与Barebox并烧录到设备
• 启动时通过指定参数（如panel=tn）验证切换效果
• 可在Barebox中用fdt print命令查看节点的status和remote-endpoint是否正确设置
• 内核启动后，通过dmesg确认LCD控制器与面板的连接状态

内容的提问来源于stack exchange，提问作者Adrian