技术分享 | i.MX8M Mini适配MIPI转eDP芯片

武汉万象奥科

技术分享 | i.MX8M Mini适配MIPI转eDP芯片 [复制链接]

方案概述

此方案使用HD-8MMN-CORE的核心板搭配TI公司的芯片SN65DSI86转换芯片实现。

SN65DSI86作为一款MIPI DSI转eDP的芯片，支持双通道DSI输入，最大四通道显示输出，最大支持4K@60fps输出，WUXGA 1080P。本方案中将采用单通道DSI输入，双通道DP输出到1080p的屏幕。

HD8MMN-CORE系列工业级核心板基于NXP(Freescale) i.MX8MM系列Cortex-A53高性能处理器设计，支持硬件加密，支持摄像头接口、USB3.0接口、HDMI/MIPI、PCIe、千兆以太网接口、多路串口等，适用于快速开发一系列最具创新性的应用，如多媒体应用、人机界面、工业4.0、车载终端以及边缘计算设备等。

2.硬件原理图

注：硬件修改REFCLK上需要贴上27M的晶振，TEST2引脚需要通过4.7K电阻上拉到1.8V.

3.软件实现

3.1软件介绍

内核版本：Linux5.10；
SN65DSI86驱动：drivers/gpu/drm/bridge/ti-sn65dsi86.c
Panel驱动：drivers/gpu/drm/panel/panel-simple.c

3.2驱动移植

内核配置，需要打开如下两项

CONFIG_DRM_TI_SN65DSI86=y

CONFIG_DRM_PANEL_SIMPLE=y

设备树配置

/ {

        osc_27m: clock-osc-27m {

                compatible = "fixed-clock";

                #clock-cells = <0>;

                clock-frequency = <27000000>;

                clock-output-names = "osc_27m";

        };



        lcd_backlight: lcd_backlight {

                compatible = "pwm-backlight";

                pwms = <&pwm1 0 100000>;

                status = "okay";



                brightness-levels = < 0  1  2  3  4  5  6  7  8  9

                                     10 11 12 13 14 15 16 17 18 19

                                     20 21 22 23 24 25 26 27 28 29

                                     30 31 32 33 34 35 36 37 38 39

                                     40 41 42 43 44 45 46 47 48 49

                                     50 51 52 53 54 55 56 57 58 59

                                     60 61 62 63 64 65 66 67 68 69

                                     70 71 72 73 74 75 76 77 78 79

                                     80 81 82 83 84 85 86 87 88 89

                                     90 91 92 93 94 95 96 97 98 99

                                    100>;

                enable-gpios = <&gpio1 1 GPIO_ACTIVE_HIGH>;

                default-brightness-level = <80>;

        };

        panel {

                compatible = "test,test-edp-1080p";        //设置自己的屏幕匹配参数组

                backlight = <&lcd_backlight>;

                no-hpd;



                port {

                        panel1_in: endpoint {

                                remote-endpoint = <&sn65_out>;

                        };

                };

        };

};
&pwm1 {

        pinctrl-names = "default";

        pinctrl-0 = <&pinctrl_pwm1>;

        status = "okay";

};


&i2c4 {

        clock-frequency = <400000>;

        pinctrl-names = "default";

        pinctrl-0 = <&pinctrl_i2c4>;

        status = "okay";

        sn65dsi86@2d {

               …….

                clock-names = "refclk";          //默认名字
                              //SN65DSI86仅支持12 MHz, 19.2 MHz, 26 MHz, 27 MHz or 38.4 MHz.

                clocks = <&osc_27m>;


               ……

                        port[url=home.php?mod=space&uid=490]@1[/url] {

                                reg = <1>;

                                sn65_out: endpoint {

                                        //data-lanes = <0 1 2 3>;
                                                                        //根据eDP屏的通道数设置，这里为2通道

                                        data-lanes = <0 1>;

 ……

驱动修改

添加显示屏的显示参数到驱动中，修改drivers/gpu/drm/panel/panel-simple.c：

tatic const struct display_timing test_edp_1080p_timing = {

        .pixelclock = { 153000000, 153000000, 153000000 },

        .hactive = { 1920, 1920, 1920 },

        .hfront_porch = { 100, 100, 100 },

        …..

        .bus_format = MEDIA_BUS_FMT_RGB666_1X18,

        .connector_type = DRM_MODE_CONNECTOR_eDP,

};



static const struct of_device_id platform_of_match[] = {

        {

                .compatible = "test,test-edp-1080p",

                .data = &test_edp_1080p,

        },

修改sn65dsi86驱动以适应我们的板卡，修改drivers/gpu/drm/bridge/ti-sn65dsi86.c，修改DSI正确的模式，防止找不到注册的panel出现报错“could not find any panel node”，开机过程中打印1次是正常的，SN65DSI86的驱动找不到Panel会被多次调用，直到找到panel为止。

static int ti_sn_bridge_attach(struct drm_bridge *bridge,

                               enum drm_bridge_attach_flags flags)

{

...
        //dsi->mode_flags = MIPI_DSI_MODE_VIDEO;

        dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_SYNC_PULSE |

                          MIPI_DSI_MODE_EOT_PACKET | MIPI_DSI_MODE_VIDEO_HSE;

调试报错

在调试过程中碰到“Link training failed, link is off”的报错，是因为SN65DSI86默认只支持ASSR模式的eDP屏幕，对于不支持ASSR模式的eDP屏，硬件上则需要将TEST2引脚拉高到1.8V，且修改相关寄存器将芯片从ASSR模式变为支持标准的DP模式，修改如下：

#define SN_ENH_FRAME_REG                        0x5A

#define  ASSR_CONTROL                           BIT(0)

...



static int ti_sn_link_training(struct ti_sn_bridge *pdata, int dp_rate_idx,

                               const char **last_err_str)

{

        unsigned int val;

        int ret;

        int i;



        /* set dp clk frequency value */

        regmap_update_bits(pdata->regmap, SN_DATARATE_CONFIG_REG,

                           DP_DATARATE_MASK, DP_DATARATE(dp_rate_idx));



        regmap_write(pdata->regmap, 0xff, 0x07);

        regmap_write(pdata->regmap, 0x16, 0x01);

        regmap_write(pdata->regmap, 0xff, 0x00);

       /* For DisplayPort, use the standard DP scrambler seed. */

        regmap_update_bits(pdata->regmap, SN_ENH_FRAME_REG,ASSR_CONTROL, 0);

        /* enable DP PLL */

        regmap_write(pdata->regmap, SN_PLL_ENABLE_REG, 1);

...

如果未接eDP屏幕会出现如下报错：

[ 2.299284] ti_sn65dsi86 3-002d: [drm:ti_sn_bridge_enable] ERROR Can't read lane count (-6); assuming 4
 [ 2.765851] ti_sn65dsi86 3-002d: [drm:ti_sn_bridge_enable] ERROR Can't read eDP rev (-6), assuming 1.1