基于STM32MP157调试MIPI-DSI屏幕

平台：STM32MP157
屏幕：mipi-dsi接口，1024x600
内核版本：linux5-4

本人是第一次调试mipi屏，在157这个平台上遇到的问题有一点多，接下来简单的描述下我的调试经验

一、先配置一下设备树DTB

&ltdc {port {#address-cells = <1>;#size-cells = <0>;ltdc_ep1_out: endpoint@1 {reg = <1>;remote-endpoint = <&dsi_in>;};};
};&dsi {#address-cells = <1>;#size-cells = <0>;status = "okay";ports {#address-cells = <1>;#size-cells = <0>;port@0 {reg = <0>;dsi_in: endpoint {remote-endpoint = <&ltdc_ep1_out>;};};port@1 {reg = <1>;dsi_out: endpoint {remote-endpoint = <&dsi_panel_in>;};};};panel@0 {compatible = "Hyb-Mipi";reg = <0>;enable-gpios = <&gpioc 6 GPIO_ACTIVE_HIGH>;   reset-gpios = <&gpioe 4 GPIO_ACTIVE_HIGH>;status = "okay";port {dsi_panel_in: endpoint {remote-endpoint = <&dsi_out>;};};};
};

二、驱动选择

在STM32MP157的源码中，自带了一个文件名为panel-simple.c通用驱动。之前已经在这个文件调通了LCD屏幕，打开文件可以看到，其实这个文件也是可以兼容mipi-dsi的屏幕。可能有些屏幕可以使用这个文件去调试，注意是看看CONFIG_DRM_MIPI_DSI这个选项有无有选择。

static int __init panel_simple_init(void)
{int err;err = platform_driver_register(&panel_simple_platform_driver);if (err < 0)return err;if (IS_ENABLED(CONFIG_DRM_MIPI_DSI)) {err = mipi_dsi_driver_register(&panel_simple_dsi_driver);if (err < 0)return err;}return 0;
}
module_init(panel_simple_init);

而我接下来调试的屏幕无法使用这个文件。

找一个类似的驱动去进行修改填充

大家可以在driver/gpu/drm/panel/源码目录下找到一个其他屏幕厂商的驱动代码进行修改。

接下来驱动代码修改：
首先是驱动和设备树适配

static const struct of_device_id hyb_of_match[] = {{ .compatible = "Hyb-Mipi", },{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, hyb_of_match);static struct mipi_dsi_driver hyb_driver = {.probe = hyb_dsi_probe,.remove = hyb_dsi_remove,.driver = {.name = "Hyb-Mipi",.of_match_table = hyb_of_match,},
};

适配成功后进入hyb_dsi_probe函数，这个函数接口主要是获取一下设备树设置的一些参数，配置一下DSI格式。

static int hyb_dsi_probe(struct mipi_dsi_device *dsi)
{struct hyb *ctx;int ret;ctx = devm_kzalloc(&dsi->dev, sizeof(*ctx), GFP_KERNEL);if (!ctx)return -ENOMEM;mipi_dsi_set_drvdata(dsi, ctx);ctx->dsi = dsi;drm_panel_init(&ctx->panel);ctx->panel.dev = &dsi->dev;ctx->panel.funcs = &hyb_funcs;ctx->reset = devm_gpiod_get(&dsi->dev, "reset", GPIOD_OUT_HIGH);if (IS_ERR(ctx->reset)) {DRM_DEV_ERROR(&dsi->dev, "Couldn't get our reset GPIO\n");return PTR_ERR(ctx->reset);} else {DRM_DEV_ERROR(&dsi->dev, "Success get our reset GPIO\n");gpiod_set_value(ctx->reset, 1);}ctx->enable = devm_gpiod_get(&dsi->dev, "enable", GPIOD_OUT_HIGH);if (IS_ERR(ctx->enable)) {DRM_DEV_ERROR(&dsi->dev, "Couldn't get our enable GPIO\n");return PTR_ERR(ctx->enable);} else {DRM_DEV_ERROR(&dsi->dev, "Success get our enable GPIO\n");gpiod_set_value(ctx->enable, 1);}ret = drm_panel_add(&ctx->panel);if (ret < 0)return ret;dsi->mode_flags = MIPI_DSI_MODE_VIDEO_HSE | MIPI_DSI_MODE_VIDEO |MIPI_DSI_CLOCK_NON_CONTINUOUS|MIPI_DSI_MODE_VIDEO_BURST;dsi->format = MIPI_DSI_FMT_RGB888;//显示格式dsi->lanes = 2;//通道return mipi_dsi_attach(dsi);
}

接下来进入hyb_get_modes()函数，这函数主要是配置屏幕参数

static const struct drm_display_mode hyb_default_mode = {.clock     = 51200,.hdisplay  = 1024,.hsync_start    = 1024 + 60,.hsync_end    = 1024 + 60 + 60,.htotal     = 1024 + 60 + 60 + 90,.vdisplay = 600,.vsync_start = 600 + 12,.vsync_end = 600 + 10 + 5,.vtotal       = 600 + 10 + 5 + 2,.vrefresh    = 60,.type = DRM_MODE_TYPE_DRIVER | DRM_MODE_TYPE_PREFERRED,
};static int hyb_get_modes(struct drm_panel *panel)
{struct drm_connector *connector = panel->connector;struct hyb *ctx = panel_to_hyb(panel);struct drm_display_mode *mode;mode = drm_mode_duplicate(panel->drm, &hyb_default_mode);if (!mode) {DRM_DEV_ERROR(&ctx->dsi->dev, "failed to add mode %ux%ux@%u\n",hyb_default_mode.hdisplay,hyb_default_mode.vdisplay,hyb_default_mode.vrefresh);return -ENOMEM;}drm_mode_set_name(mode);drm_mode_probed_add(connector, mode);return 1;
}

接下来就是进入hyb_prepare()函数，MIPI_DSI_MODE_LPM表示默认在 LP 模式下发送初始化序列。这个很重要，因为需要我们发送一个初始化序列到mipi屏上。

static const struct hyb_init_cmd hyb_init_cmds[] = {{ .data = { 0x80, 0x8B } },{ .data = { 0x81, 0x78 } },{ .data = { 0x82, 0x78 } },{ .data = { 0x83, 0x78 } },{ .data = { 0x84, 0x78 } },{ .data = { 0x85, 0x78 } },{ .data = { 0x86, 0x78 } },
};static int hyb_prepare(struct drm_panel *panel)
{struct hyb *ctx = panel_to_hyb(panel);struct mipi_dsi_device *dsi = ctx->dsi;unsigned int i;int ret;gpiod_set_value(ctx->reset, 1);dsi->mode_flags |= MIPI_DSI_MODE_LPM;msleep(200);/* Select User Command Set table (CMD1) */ret = mipi_dsi_generic_write(dsi, (u8[]){ 0xfe, 0x00 }, 2);if (ret < 0) {DRM_DEV_ERROR(dev, "Failed to Set table (%d)\n", ret);    }/* Software reset */ret = mipi_dsi_dcs_soft_reset(dsi);       /* 0x01 */if (ret < 0) {DRM_DEV_ERROR(dev, "Failed to do Software Reset (%d)\n", ret);//return -1;}usleep_range(5000, 10000);      /* > 5ms *///发送初始化序列for (i = 0; i < ARRAY_SIZE(hyb_init_cmds); i++) {const struct hyb_init_cmd *cmd =&hyb_init_cmds[i];ret = mipi_dsi_dcs_write_buffer(dsi, cmd->data,HYB_INIT_CMD_LEN);if (ret < 0) {return ret;}}ret = mipi_dsi_generic_write(dsi, (u8[]){ 0xC2, 0x0B }, 2);if (ret < 0) {printk("Failed to set DSI mode\n");  //dev_err(dev, "Failed to set DSI mode (%d)\n", ret);//goto fail;}ret = mipi_dsi_generic_write(dsi, (u8[]){ 0xB2, 0x10 }, 2);if (ret < 0) {//dev_err(dev, "Failed to set DSI mode (%d)\n", ret);//goto fail;}u8 buffer[2] = {0xB2, 0x10};int value = 0;ret = mipi_dsi_generic_read(dsi, &buffer[0], 1, (void *)&value, sizeof(value));printk("MIPI_DSI_DEBUG: Reg.%02x Set.%02x Get.%02x Ret.%d Flag.%c\n",buffer[0], buffer[1], value, ret, ((buffer[1] == value) ? 'T' : 'F'));/* Set pixel format */ret = mipi_dsi_dcs_set_pixel_format(dsi, 0x77);//dev_dbg(dev, "Interface color format set to 0x%x\n", color_format);if (ret < 0) {printk("Failed to set pixel format\n");//dev_err(dev, "Failed to set pixel format (%d)\n", ret);//goto fail;}/* Exit sleep mode */ret = mipi_dsi_dcs_exit_sleep_mode(dsi);   /* 0x11 */if (ret < 0) {printk("Failed to exit sleep mode\n");//DRM_DEV_ERROR(&dsi->dev, "Failed to exit sleep mode (%d)\n", ret);//goto fail;}usleep_range(120000, 125000);              /* > 120ms */ret = mipi_dsi_dcs_set_display_on(dsi);        /* 0x29 */if (ret < 0) {printk("Failed to set display ON\n");//DRM_DEV_ERROR(&dsi->dev, "Failed to set display ON (%d)\n", ret);//goto fail;}usleep_range(5000, 10000);                   /* > 5ms */return 0;
}

由于这个屏幕默认是四个通道，但是STM32MP157最多只有两个通道，通过厂商提供的手册，可以通过寄存器进行通道选择的配置。这时候我们在发完初始化序列后，再发配置通道的指令语句，然后，为了验证发送的指令是否改变了MIPI芯片的寄存器，可以进行读取。这样可以保证万无一失，也可以确定是否发送成功，走少很多弯路。

//写入参数
ret = mipi_dsi_generic_write(dsi, (u8[]){ 0xB2, 0x10 }, 2);if (ret < 0) {}u8 buffer[2] = {0xB2, 0x10};int value = 0;//读取对应的寄存器ret = mipi_dsi_generic_read(dsi, &buffer[0], 1, (void *)&value, sizeof(value));printk("MIPI_DSI_DEBUG: Reg.%02x Set.%02x Get.%02x\n",buffer[0], buffer[1], value);

如果顺利的话，基本上开机就能正常启动屏幕了。

调试过程中遇到的坑

第一个问题：在驱动加载中IO口申请失败

我在这个问题停留了有一段时间，用了各种办法都不知道，然后进入系统，手动申请又可以成功。然后把驱动变成模块进去就可以申请成功了，那这个问题就很明显是驱动加载顺序的问题导致的。
问题解决方案：
在内核源码中include/linux/init.h文件定义了加载优先级

我看了一下引脚子系统加载的优先级是arch_initcall
而我们经常使用的module_init()是 device_initcall(fn)，驱动对应的加载的优先级为6。所以可以在之后在加载。

static int __init panel_simple_init(void)
{int err;if (IS_ENABLED(CONFIG_DRM_MIPI_DSI)) {err = mipi_dsi_driver_register(&hyb_driver);if (err < 0)return err;}return 0;
}
module_init(panel_simple_init);
static void __exit panel_simple_exit(void)
{if (IS_ENABLED(CONFIG_DRM_MIPI_DSI))mipi_dsi_driver_unregister(&hyb_driver);}
module_exit(panel_simple_exit);
//module_mipi_dsi_driver(hyb_driver);把这个给屏蔽了，把module_init(）添加进去

第二个问题:一直报stm32-display-dsi 5a000000.dsi: Read payload FIFO is empty

[    3.000353] Hyb-Mipi 5a000000.dsi.0: [drm:hyb_dsi_probe]  Success get our reset GPIO
[    3.007902] Hyb-Mipi 5a000000.dsi.0: [drm:hyb_dsi_probe]  Success get our enable GPIO
[    3.020736] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[    3.025898] [drm] Driver supports precise vblank timestamp query.
[    3.033213] [drm] Initialized stm 1.0.0 20170330 for 5a001000.display-controller on minor 0
[    3.388206] stm32-display-dsi 5a000000.dsi: Read payload FIFO is empty
[    3.409780] stm32-display-dsi 5a000000.dsi: Read payload FIFO is empty
[    3.431353] stm32-display-dsi 5a000000.dsi: Read payload FIFO is empty
[    3.431368] MIPI_DSI_DEBUG: Reg.b2 Set.10 Get.00
[    3.819225] Console: switching to colour frame buffer device 128x37
[    3.880960] stm32-display 5a001000.display-controller: fb0: stmdrmfb frame buffer device

这个问题是没有在代码中添加dsi->mode_flags |= MIPI_DSI_MODE_LPM;
这个直接关于能否正常发送指令和获取寄存器值。

总结：

在现有的条件下，多去对比类似的驱动编写的模式，从中找到规律，并且结合自身的屏幕问题去修改和补充。