Linux的LCD驱动分析及移植

测试平台

宿主机平台：Ubuntu 12.04.4 LTS

目标机：Easy-ARM IMX283

目标机内核：Linux 2.6.35.3

LCD驱动分析

LCD屏的驱动总体上分成两块，一块是GUI显示输出驱动；一块是触摸驱动（该部分单独一节另外描述）。

LCD驱动概念

LCD是Liquid Crystal Display的简称，也就是经常所说的液晶显示器。LCD能够支持彩色图像的显示和视频的播放，是一种非常重要的输出设备。如果我们的系统要用GUI（图形界面接口），比如minigui，MicroWindows。这时LCD设备驱动程序就应该编写成frambuffer接口，而不是编写成仅仅操作底层的LCD控制器接口。

framebuffer是Linux系统为显示设备提供的一个接口，它将显示缓冲区抽象，屏蔽图像硬件的底层差异，允许上层应用程序在图形模式下直接对显示缓冲区进行操作。framebuffer又叫帧缓冲，是Linux为操作显示设备提供的一个用户接口。用户应用程序可以通过framebuffer透明地访问不同类型的显示设备。从这个方面来说，framebuffer是硬件设备显示缓冲区的抽象。Linux抽象出framebuffer这个帧缓冲区可以供用户应用程序直接读写，通过更改framebuffer中的内容，就可以立刻显示在LCD显示屏上。

framebuffer是一个标准的字符设备，主设备号是29，次设备号根据缓冲区的数目而定。framebuffer对应/dev/fb%d设备文件。根据显卡的多少，设备文件可能是/dev/fb0、/dev/fb1等。缓冲区设备也是一种普通的内存设备,可以直接对其进行读写。对用户程序而言，它和/dev下面的其他设备没有什么区别，用户可以把frameBuffer看成一块内存，既可以写，又可以读。显示器将根据内存数据显示对应的图像界面。这一切都由LCD控制器和响应的驱动程序来完成。

LCD驱动框架分析

总体上是一个平台设备驱动与字符驱动的组合；

先从LCD的设备 dev/fb* 是怎么实现的来进行追溯；

1.开发板启动，进行设备注册；

在  arch/arm/mach-mx28/device.c  设备注册文件中，注册LCD的fd平台设备 “mxs-fb”

// mxs-fb平台设备资源定义
static struct resource framebuffer_resource[] = {
    {
     .flags = IORESOURCE_MEM,
     .start = LCDIF_PHYS_ADDR,
     .end   = LCDIF_PHYS_ADDR + 0x2000 - 1,
     },
    {
     .flags = IORESOURCE_IRQ,
     .start = IRQ_LCDIF,
     .end   = IRQ_LCDIF,
     },
};

// mxs-fb平台设备私有数据，包含显示屏名称、分辨率、位宽、时钟、面板操作等，在drivers/video/mxs/lcd_43wvf1g.c 中通过subsys_initcall 接口将设备私有数据添加到链表中

static struct mxs_platform_fb_data mxs_framebuffer_pdata = {
    .list = LIST_HEAD_INIT(mxs_framebuffer_pdata.list),
};

// lcd设备启动初始化，在 m28evk.c 中 mx28_device_init()会调用

static void __init mx28_init_lcdif(void)
{
    struct platform_device *pdev;
    pdev = mxs_get_device("mxs-fb", 0);　　//获取匹配的设备结构体，定义在 arch/arm/plat-mxs/device.c 中

if (pdev == NULL || IS_ERR(pdev))
        return;
    pdev->resource = framebuffer_resource;
    pdev->num_resources = ARRAY_SIZE(framebuffer_resource);
    pdev->dev.platform_data = &mxs_framebuffer_pdata;
    mxs_add_device(pdev, 3);　　// 添加到设备注册列表，设备注册在 arch/arm/plat-mxs/device.c 中实现 通过 device_initcall(mxs_device_init);遍历设备列表并进行平台设备注册

}

2.接下来是 platform_driver   mxsfb_driver 的注册，匹配之后触发 mxsfb_probe 函数执行以下操作：

进行相关硬件初始化和 framebuffer 设置；

register_framebuffer()  注册 LCD 屏的 fd 设备;

 

LCD的驱动包含：

drivers/video/mxs/lcd_43wvf1g.c　　// LCD设备私有数据，包含名称、分辨率、位宽、时钟、面板操作

drivers/video/mxs/lcdif.c　　　　　  // lcd的一些接口操作

drivers/video/mxs/mxsfb.c　　　　  // 

平台设备驱动 platform_driver 注册  drivers/video/mxs/mxsfb.c 

会编译成 mxsfb.ko

static struct platform_driver mxsfb_driver = {
    .probe = mxsfb_probe,
    .remove = mxsfb_remove,
    .suspend = mxsfb_suspend,
    .resume = mxsfb_resume,
    .driver = {
           .name = "mxs-fb",　　　　// 与启动时的平台设备注册的 platform_device 名称相同
           .owner = THIS_MODULE,
           },
};

static int __init mxsfb_init(void)
{
    return platform_driver_register(&mxsfb_driver);　　// 显示屏平台设备驱动注册
}

驱动安装时与平台设备匹配之后触发 mxsfb_probe 函数，这个时核心。

static int __devinit mxsfb_probe(struct platform_device *pdev)
{
    int ret = 0;
    struct mxs_fb_data *data;
    struct resource *res;
    struct fb_info *info;
    struct mxs_platform_fb_data *pdata = pdev->dev.platform_data;
    struct mxs_platform_fb_entry *pentry = NULL;

    mydbg("\n");
    if (pdata == NULL) {
        ret = -ENODEV;
        goto out;
    }

    if (default_panel_name) {
        mydbg("default_panel_name=%s\n",default_panel_name);
　　　　 // 通过LCD面板名称匹配获取面板参数及设置句柄（平台设备私有数据传递过来）
        pentry = (void *)mxs_lcd_iterate_pdata(pdata,
                               get_matching_pentry_by_name,
                               default_panel_name);
        if (pentry) {
            mxs_lcd_move_pentry_up(pentry, pdata);
            pdata->cur = pentry;
        }
    }
    if (!default_panel_name || !pentry) {
        mydbg("\n");
        pentry = pdata->cur;
    }
    if (!pentry || !pentry->init_panel || !pentry->run_panel ||
        !pentry->release_panel) {
        mydbg("\n");
        ret = -EINVAL;
        goto out;
    }

    data =
        (struct mxs_fb_data *)framebuffer_alloc(sizeof(struct mxs_fb_data) +
                            sizeof(u32) * 256 -
                            sizeof(struct fb_info),
                            &pdev->dev);
    if (data == NULL) {
        ret = -ENOMEM;
        goto out;
    }

    cdata = data;
    data->dev = &pdev->dev;
    data->pdata = pdata;
    platform_set_drvdata(pdev, data);
    info = &data->info;

    dev_dbg(&pdev->dev, "resolution %dx%d, bpp %d\n", pentry->x_res,
        pentry->y_res, pentry->bpp);

    mxs_lcd_iterate_pdata(pdata, get_max_memsize, data);

    data->map_size = PAGE_ALIGN(data->mem_size) * NUM_SCREENS;
    dev_dbg(&pdev->dev, "memory to allocate: %d\n", data->map_size);

    data->virt_start = dma_alloc_writecombine(&pdev->dev,
                          data->map_size,
                          &data->phys_start,
                          GFP_KERNEL);

    if (data->virt_start == NULL) {
        ret = -ENOMEM;
        goto out_dma;
    }
    dev_dbg(&pdev->dev, "allocated at %p:0x%x\n", data->virt_start,
        data->phys_start);
    mutex_init(&data->blank_mutex);
    INIT_WORK(&data->work, mxsfb_task);
    data->state = F_ENABLE;

    mxsfb_default.bits_per_pixel = pentry->bpp;
    /* NB: rotated */
    mxsfb_default.xres = pentry->y_res;
    mxsfb_default.yres = pentry->x_res;
    mxsfb_default.xres_virtual = pentry->y_res;
    mxsfb_default.yres_virtual = data->map_size /
        (pentry->y_res * pentry->bpp / 8);
    if (mxsfb_default.yres_virtual >= mxsfb_default.yres * 2)
        mxsfb_default.yres_virtual = mxsfb_default.yres * 2;
    else
        mxsfb_default.yres_virtual = mxsfb_default.yres;

    mxsfb_fix.smem_start = data->phys_start;
    mxsfb_fix.smem_len = pentry->y_res * pentry->x_res * pentry->bpp / 8;
    mxsfb_fix.ypanstep = 1;

    switch (pentry->bpp) {
    case 32:
    case 24:
        mxsfb_default.red.offset = 16;
        mxsfb_default.red.length = 8;
        mxsfb_default.green.offset = 8;
        mxsfb_default.green.length = 8;
        mxsfb_default.blue.offset = 0;
        mxsfb_default.blue.length = 8;
        break;

    case 16:
#if 0
        mxsfb_default.red.offset = 11;
        mxsfb_default.red.length = 5;
        mxsfb_default.green.offset = 5;
        mxsfb_default.green.length = 6;
        mxsfb_default.blue.offset = 0;
        mxsfb_default.blue.length = 5;
        break;
#else
        mxsfb_default.red.offset = 0 ;
        mxsfb_default.red.length = 5;
        mxsfb_default.green.offset = 5;
        mxsfb_default.green.length = 6;
        mxsfb_default.blue.offset = 11;
        mxsfb_default.blue.length = 5;
        break;
#endif
    default:
        dev_err(&pdev->dev, "unsupported bitwidth %d\n", pentry->bpp);
        ret = -EINVAL;
        goto out_dma;
    }

    info->screen_base = data->virt_start;
    info->fbops = &mxsfb_ops;
    info->var = mxsfb_default;
    info->fix = mxsfb_fix;
    info->pseudo_palette = &data->par;
    data->par = NULL;
    info->flags = FBINFO_FLAG_DEFAULT;

    init_waitqueue_head(&data->vsync_wait_q);
    data->vsync_count = 0;

    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (res == NULL) {
        dev_err(&pdev->dev, "cannot get IRQ resource\n");
        ret = -ENODEV;
        goto out_dma;
    }
    data->regbase = (unsigned long)IO_ADDRESS(res->start);

    res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
    if (res == NULL) {
        dev_err(&pdev->dev, "cannot get IRQ resource\n");
        ret = -ENODEV;
        goto out_dma;
    }
    data->irq = res->start;

    mxsfb_check_var(&info->var, info);

    ret = fb_alloc_cmap(&info->cmap, 256, 0);
    if (ret)
        goto out_cmap;

    mxsfb_set_par(info);

    mxs_init_lcdif();
    ret = pentry->init_panel(data->dev, data->phys_start,
                 mxsfb_fix.smem_len, pentry);
    if (ret) {
        dev_err(&pdev->dev, "cannot initialize LCD panel\n");
        goto out_panel;
    }
    dev_dbg(&pdev->dev, "LCD panel initialized\n");
    init_timings(data); // not effect dotclk mode

    ret = request_irq(data->irq, lcd_irq_handler, 0, "fb_irq", data);
    if (ret) {
        dev_err(&pdev->dev, "request_irq (%d) failed with error %d\n",
            data->irq, ret);
        goto out_panel;
    }
    ret = register_framebuffer(info);    // 注册fb_info
    if (ret)
        goto out_irq;

    pentry->run_panel();
    /* REVISIT: temporary workaround for MX23EVK */
    mxsfb_disable_controller(data);
    mxsfb_enable_controller(data);
    data->cur_phys = data->phys_start;
    dev_dbg(&pdev->dev, "LCD running now\n");

#ifdef CONFIG_CPU_FREQ
    mxsfb_nb.fb_data = data;
    cpufreq_register_notifier(&mxsfb_nb.nb, CPUFREQ_TRANSITION_NOTIFIER);
#endif /* CONFIG_CPU_FREQ */

    goto out;

out_irq:
    free_irq(data->irq, data);
out_panel:
    fb_dealloc_cmap(&info->cmap);
out_cmap:
    dma_free_writecombine(&pdev->dev, data->map_size, data->virt_start,
                  data->phys_start);
out_dma:
    kfree(data);
out:
    return ret;
}

待续.....

LCD驱动移植总结

1.LCD引脚配置及初始化

上述原理图包含了数据、时钟、背光控制、触摸、复位等引脚的分配，具体有机会在深入理解LCD硬件驱动原理有在进行说明。

在 arch/arm/mach-mx28/mx28evk_pins.c 的 mx28evk_fixed_pins[ ] 引脚列表中添加 LCD 的驱动引脚，相关引脚转义在  mx28_pins.h 结合 arch/arm/mach/pinctrl.h 实现

#if defined(CONFIG_FB_MXS) || defined(CONFIG_FB_MXS_MODULE)
    {
     .name  = "LCD_D00",
     .id    = PINID_LCD_D00,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D01",
     .id    = PINID_LCD_D01,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D02",
     .id    = PINID_LCD_D02,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D03",
     .id    = PINID_LCD_D03,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D04",
     .id    = PINID_LCD_D04,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D05",
     .id    = PINID_LCD_D05,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D06",
     .id    = PINID_LCD_D06,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D07",
     .id    = PINID_LCD_D07,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D08",
     .id    = PINID_LCD_D08,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D09",
     .id    = PINID_LCD_D09,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D10",
     .id    = PINID_LCD_D10,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D11",
     .id    = PINID_LCD_D11,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D12",
     .id    = PINID_LCD_D12,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D13",
     .id    = PINID_LCD_D13,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D14",
     .id    = PINID_LCD_D14,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D15",
     .id    = PINID_LCD_D15,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
/*
    {
     .name  = "LCD_D16",
     .id    = PINID_LCD_D16,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D17",
     .id    = PINID_LCD_D17,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D18",
     .id    = PINID_LCD_D18,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D19",
     .id    = PINID_LCD_D19,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D20",
     .id    = PINID_LCD_D20,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D21",
     .id    = PINID_LCD_D21,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D22",
     .id    = PINID_LCD_D22,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name  = "LCD_D23",
     .id    = PINID_LCD_D23,
     .fun    = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage    = PAD_3_3V,
     .drive    = 1,
     },
*/
    {
     .name = "LCD_RESET",
     .id = PINID_LCD_RESET,
     .fun = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name = "LCD_VSYNC",
     .id   = PINID_LCD_RD_E,
     .fun  = PIN_FUN2,
     .strength = PAD_8MA,
     .voltage = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name = "LCD_HSYNC",
     .id = PINID_LCD_WR_RWN,
     .fun = PIN_FUN2,
     .strength = PAD_8MA,
     .voltage = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name = "LCD_ENABLE",
     .id = PINID_LCD_CS,
     .fun = PIN_FUN2,
     .strength = PAD_8MA,
     .voltage = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name = "LCD_DOTCLK",
     .id = PINID_LCD_RS,
     .fun = PIN_FUN2,
     .strength = PAD_8MA,
     .voltage = PAD_3_3V,
     .drive    = 1,
     },
    {
     .name = "LCD_BACKLIGHT",
     .id = PINID_PWM3,
     .fun = PIN_FUN1,
     .strength = PAD_8MA,
     .voltage = PAD_3_3V,
     .drive    = 1,
     },
#endif

然后通过类似 LCDIF_PHYS_ADDR + BM_LCDIF_CTRL1_RESET 组合就可以操作相关引脚寄存器了

2. 驱动移植到drivers 目录

1）.将LCD驱动放到 drivers/video/ 目录下，本例为 mxs

2）.修改 drivers/video/Kconfig，添加如下配置，表示会提取 mxs 驱动的 Kconfig 配置

if ARCH_MXS
source "drivers/video/mxs/Kconfig"
endif

3. 修改板级文件

板级文件有两个

mach-mx28 　　// mx28系列特有的

plat-mxs　　　  // fsl通用共有的功能

1）在设备注册 arch/arm/mach-mx28/device.c 中添加 mxs LCD 平台设备注册

#if defined(CONFIG_FB_MXS) || defined(CONFIG_FB_MXS_MODULE)
// LCD平台设备资源 resource
static struct resource framebuffer_resource[] = {
    {
     .flags = IORESOURCE_MEM,　　　　//寻址地址空间资源

     .start = LCDIF_PHYS_ADDR,
     .end   = LCDIF_PHYS_ADDR + 0x2000 - 1,
     },
    {
     .flags = IORESOURCE_IRQ,　　　//中断资源
     .start = IRQ_LCDIF,
     .end   = IRQ_LCDIF,
     },
};

static struct mxs_platform_fb_data mxs_framebuffer_pdata = {
    .list = LIST_HEAD_INIT(mxs_framebuffer_pdata.list),
};

static void __init mx28_init_lcdif(void)
{
    struct platform_device *pdev;
    pdev = mxs_get_device("mxs-fb", 0);　　//获取匹配的设备结构体，定义在 arch/arm/plat-mxs/device.c 中
    if (pdev == NULL || IS_ERR(pdev))
        return;
    pdev->resource = framebuffer_resource;
    pdev->num_resources = ARRAY_SIZE(framebuffer_resource);
    pdev->dev.platform_data = &mxs_framebuffer_pdata; //设备私有数据链表，包含名称、分辨率、位宽、时钟、面板操作，在drivers/video/mxs/lcd_43wvf1g.c 中通过subsys_initcall 接口将设备私有数据添加到链表中

    mxs_add_device(pdev, 3);　　//添加到设备注册列表
}
#else
static void __init mx28_init_lcdif(void)
{
    ;
}
#endif

2）在设备列表注册 arch/arm/plat-mxs/device.c 中添加 mxs LCD 平台设备结构及设备列表匹配信息

#if defined(CONFIG_FB_MXS) || defined(CONFIG_FB_MXS_MODULE)
// LCD面板平台设备结构体
static struct platform_device mxs_fb = {
    .name    = "mxs-fb",　　//平台设备名称，后面的平台设备驱动名称要与这个一致
    .id    = 0,
    .dev = {
        .dma_mask           = &common_dmamask,
        .coherent_dma_mask      = DMA_BIT_MASK(32),
        .release = mxs_nop_release,
        },
};
#endif

static struct mxs_dev_lookup dev_lookup[] = {
......

#if defined(CONFIG_FB_MXS) || defined(CONFIG_FB_MXS_MODULE)
    {
     .name    = "mxs-fb",
     .size    = 1,
     .pdev    = &mxs_fb,
     },
#endif

......
}