S3C2440上LCD驅動(FrameBuffer)實例開發講解（二）

原文出處：http://bbs.chinaunix.net/thread-3634288-1-1.html

開發環境

• 主  機：VMWare--Fedora 9
• 開發板：Mini2440--64MB Nand, Kernel:2.6.30.4
• 編譯器：arm-linux-gcc-4.3.2

上接：S3C2440上LCD驅動(FrameBuffer)實例開發詳解（一）

四、幀緩衝(FrameBuffer)設備驅動實例代碼：

①、建立驅動文件：my2440_lcd.c，依就是驅動程序的最基本結構：FrameBuffer驅動的初始化和卸載部分及其他，如下：

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/dma-mapping.h>
#include <linux/fb.h>
#include <linux/clk.h>
#include <linux/interrupt.h>
#include <linux/mm.h>

#include <linux/slab.h>
#include <linux/delay.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <asm/div64.h>
#include <mach/regs-lcd.h>
#include <mach/regs-gpio.h>
#include <mach/fb.h>
#include <linux/pm.h>

/*FrameBuffer設備名稱*/
static char driver_name[] = "my2440_lcd";

/*定義一個結構體用來維護驅動程序中各函數中用到的變量
  先別看結構體要定義這些成員，到各函數使用的地方就明白了*/
struct my2440fb_var
{
    int lcd_irq_no;           /*保存LCD中斷號*/
    struct clk *lcd_clock;    /*保存從平臺時鐘隊列中獲取的LCD時鐘*/
    struct resource *lcd_mem; /*LCD的IO空間*/
    void __iomem *lcd_base;   /*LCD的IO空間映射到虛擬地址*/
    struct device *dev;

    struct s3c2410fb_hw regs; /*表示5個LCD配置寄存器，s3c2410fb_hw定義在mach-s3c2410/include/mach/fb.h中*/

    /*定義一個數組來充當調色板。
    據數據手冊描述，TFT屏色位模式爲8BPP時，調色板(顏色表)的長度爲256，調色板起始地址爲0x4D000400*/
    u32    palette_buffer[256]; 

    u32 pseudo_pal[16];   
    unsigned int palette_ready; /*標識調色板是否準備好了*/
};

/*用做清空調色板(顏色表)*/
#define PALETTE_BUFF_CLEAR (0x80000000)    

/*LCD平臺驅動結構體，平臺驅動結構體定義在platform_device.h中，該結構體成員接口函數在第②步中實現*/
static struct platform_driver lcd_fb_driver =
{
    .probe     = lcd_fb_probe,               /*FrameBuffer設備探測*/
    .remove    = __devexit_p(lcd_fb_remove), /*FrameBuffer設備移除*/
    .suspend   = lcd_fb_suspend,             /*FrameBuffer設備掛起*/
    .resume    = lcd_fb_resume,              /*FrameBuffer設備恢復*/
    .driver    =
    {
        /*注意這裏的名稱一定要和系統中定義平臺設備的地方一致，這樣才能把平臺設備與該平臺設備的驅動關聯起來*/
        .name = "s3c2410-lcd",
        .owner = THIS_MODULE,
    },
};

static int __init lcd_init(void)
{
    /*在Linux中，幀緩衝設備被看做是平臺設備，所以這裏註冊平臺設備*/
    return platform_driver_register(&lcd_fb_driver);
}

static void __exit lcd_exit(void)
{
    /*註銷平臺設備*/
    platform_driver_unregister(&lcd_fb_driver);
}

module_init(lcd_init);
module_exit(lcd_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Huang Gang");
MODULE_DESCRIPTION("My2440 LCD FrameBuffer Driver");

②、LCD平臺設備各接口函數的實現：

/*LCD FrameBuffer設備探測的實現，注意這裏使用一個__devinit宏，到lcd_fb_remove接口函數實現的地方講解*/
static int __devinit lcd_fb_probe(struct platform_device *pdev)
{
    int i;
    int ret;
    struct resource *res;  /*用來保存從LCD平臺設備中獲取的LCD資源*/
    struct fb_info  *fbinfo; /*FrameBuffer驅動所對應的fb_info結構體*/
    struct s3c2410fb_mach_info *mach_info; /*保存從內核中獲取的平臺設備數據*/
    struct my2440fb_var *fbvar; /*上面定義的驅動程序全局變量結構體*/
    struct s3c2410fb_display *display; /*LCD屏的配置信息結構體，該結構體定義在mach-s3c2410/include/mach/fb.h中*/

    /*獲取LCD硬件相關信息數據，在前面講過內核使用s3c24xx_fb_set_platdata函數將LCD的硬件相關信息保存到
     了LCD平臺數據中，所以這裏我們就從平臺數據中取出來在驅動中使用*/
    mach_info = pdev->dev.platform_data;
    if(mach_info == NULL)
    {
        /*判斷獲取數據是否成功*/
        dev_err(&pdev->dev, "no platform data for lcd\n");
        return -EINVAL;
    }

    /*獲得在內核中定義的FrameBuffer平臺設備的LCD配置信息結構體數據*/
    display = mach_info->displays + mach_info->default_display;

    /*給fb_info分配空間，大小爲my2440fb_var結構的內存，framebuffer_alloc定義在fb.h中在fbsysfs.c中實現*/
    fbinfo = framebuffer_alloc(sizeof(struct my2440fb_var), &pdev->dev);
    if(!fbinfo)
    {
        dev_err(&pdev->dev, "framebuffer alloc of registers failed\n");
        ret = -ENOMEM;
        goto err_noirq;
    }
    platform_set_drvdata(pdev, fbinfo);/*重新將LCD平臺設備數據設置爲fbinfo，好在後面的一些函數中來使用*/

    /*這裏的用途其實就是將fb_info的成員par(注意是一個void類型的指針)指向這裏的私有變量結構體fbvar，
     目的是到其他接口函數中再取出fb_info的成員par，從而能繼續使用這裏的私有變量*/
    fbvar = fbinfo->par;
    fbvar->dev = &pdev->dev;

    /*在系統定義的LCD平臺設備資源中獲取LCD中斷號,platform_get_irq定義在platform_device.h中*/
    fbvar->lcd_irq_no = platform_get_irq(pdev, 0);
    if(fbvar->lcd_irq_no < 0)
    {
        /*判斷獲取中斷號是否成功*/
        dev_err(&pdev->dev, "no lcd irq for platform\n");
        return -ENOENT;
    }

    /*獲取LCD平臺設備所使用的IO端口資源，注意這個IORESOURCE_MEM標誌和LCD平臺設備定義中的一致*/
    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if(res == NULL)
    {
        /*判斷獲取資源是否成功*/
        dev_err(&pdev->dev, "failed to get memory region resource\n");
        return -ENOENT;
    }

    /*申請LCD IO端口所佔用的IO空間(注意理解IO空間和內存空間的區別),request_mem_region定義在ioport.h中*/
    fbvar->lcd_mem = request_mem_region(res->start, res->end - res->start + 1, pdev->name);
    if(fbvar->lcd_mem == NULL)
    {
        /*判斷申請IO空間是否成功*/
        dev_err(&pdev->dev, "failed to reserve memory region\n");
        return -ENOENT;
    }

    /*將LCD的IO端口占用的這段IO空間映射到內存的虛擬地址，ioremap定義在io.h中
     注意：IO空間要映射後才能使用，以後對虛擬地址的操作就是對IO空間的操作*/
    fbvar->lcd_base = ioremap(res->start, res->end - res->start + 1);
    if(fbvar->lcd_base == NULL)
    {
        /*判斷映射虛擬地址是否成功*/
        dev_err(&pdev->dev, "ioremap() of registers failed\n");
        ret = -EINVAL;
        goto err_nomem;
    }

    /*從平臺時鐘隊列中獲取LCD的時鐘，這裏爲什麼要取得這個時鐘，從LCD屏的時序圖上看，各種控制信號的延遲
     都跟LCD的時鐘有關。系統的一些時鐘定義在arch/arm/plat-s3c24xx/s3c2410-clock.c中*/
    fbvar->lcd_clock = clk_get(NULL, "lcd");
    if(!fbvar->lcd_clock)
    {
        /*判斷獲取時鐘是否成功*/
        dev_err(&pdev->dev, "failed to find lcd clock source\n");
        ret = -ENOENT;
        goto err_nomap;
    }
    /*時鐘獲取後要使能後纔可以使用，clk_enable定義在arch/arm/plat-s3c/clock.c中*/
    clk_enable(fbvar->lcd_clock);

    /*申請LCD中斷服務，上面獲取的中斷號lcd_fb_irq，使用快速中斷方式:IRQF_DISABLED
     中斷服務程序爲:lcd_fb_irq，將LCD平臺設備pdev做參數傳遞過去了*/
    ret = request_irq(fbvar->lcd_irq_no, lcd_fb_irq, IRQF_DISABLED, pdev->name, fbvar);
    if(ret)
    {
        /*判斷申請中斷服務是否成功*/
        dev_err(&pdev->dev, "IRQ%d error %d\n", fbvar->lcd_irq_no, ret);
        ret = -EBUSY;
        goto err_noclk;
    }
    /*好了，以上是對要使用的資源進行了獲取和設置。下面就開始初始化填充fb_info結構體*/

    /*首先初始化fb_info中代表LCD固定參數的結構體fb_fix_screeninfo*/
    /*像素值與顯示內存的映射關係有5種，定義在fb.h中。現在採用FB_TYPE_PACKED_PIXELS方式，在該方式下，
    像素值與內存直接對應，比如在顯示內存某單元寫入一個"1"時，該單元對應的像素值也將是"1"，這使得應用層
    把顯示內存映射到用戶空間變得非常方便。Linux中當LCD爲TFT屏時，顯示驅動管理顯示內存就是基於這種方式*/
    strcpy(fbinfo->fix.id, driver_name);/*字符串形式的標識符*/
    fbinfo->fix.type = FB_TYPE_PACKED_PIXELS;
    fbinfo->fix.type_aux = 0;/*以下這些根據fb_fix_screeninfo定義中的描述，當沒有硬件是都設爲0*/
    fbinfo->fix.xpanstep = 0;
    fbinfo->fix.ypanstep = 0;
    fbinfo->fix.ywrapstep= 0;
    fbinfo->fix.accel = FB_ACCEL_NONE;

    /*接着，再初始化fb_info中代表LCD可變參數的結構體fb_var_screeninfo*/
    fbinfo->var.nonstd          = 0;
    fbinfo->var.activate        = FB_ACTIVATE_NOW;
    fbinfo->var.accel_flags     = 0;
    fbinfo->var.vmode           = FB_VMODE_NONINTERLACED;
    fbinfo->var.xres            = display->xres;
    fbinfo->var.yres            = display->yres;
    fbinfo->var.bits_per_pixel  = display->bpp;

    /*指定對底層硬件操作的函數指針, 因內容較多故其定義在第③步中再講*/
    fbinfo->fbops               =&my2440fb_ops;

    fbinfo->flags               = FBINFO_FLAG_DEFAULT;

    fbinfo->pseudo_palette      = &fbvar->pseudo_pal;

 

    /*初始化色調色板(顏色表)爲空*/
    for(i = 0; i < 256; i++)
    {
        fbvar->palette_buffer[i]= PALETTE_BUFF_CLEAR;
    }

    for (i = 0; i < mach_info->num_displays; i++) /*fb緩存的長度*/
    {
        /*計算FrameBuffer緩存的最大大小，這裏右移3位(即除以8)是因爲色位模式BPP是以位爲單位*/
        unsigned long smem_len = (mach_info->displays[i].xres * mach_info->displays[i].yres * mach_info->displays[i].bpp) >> 3;

        if(fbinfo->fix.smem_len < smem_len)
        {
            fbinfo->fix.smem_len = smem_len;
        }
    }

    /*初始化LCD控制器之前要延遲一段時間*/
    msleep(1);

    /*初始化完fb_info後，開始對LCD各寄存器進行初始化，其定義在後面講到*/
    my2440fb_init_registers(fbinfo);

    /*初始化完寄存器後，開始檢查fb_info中的可變參數，其定義在後面講到*/
    my2440fb_check_var(fbinfo);
    
    /*申請幀緩衝設備fb_info的顯示緩衝區空間，其定義在後面講到*/
    ret = my2440fb_map_video_memory(fbinfo);
    if (ret)
    {
        dev_err(&pdev->dev, "failed to allocate video RAM: %d\n", ret);
        ret = -ENOMEM;
        goto err_nofb;
    }

    /*最後，註冊這個幀緩衝設備fb_info到系統中, register_framebuffer定義在fb.h中在fbmem.c中實現*/
    ret = register_framebuffer(fbinfo);
    if (ret < 0)
    {
        dev_err(&pdev->dev, "failed to register framebuffer device: %d\n", ret);
        goto err_video_nomem;
    }

    /*對設備文件系統的支持(對設備文件系統的理解請參閱：嵌入式Linux之我行——設備文件系統剖析與使用)
     創建frambuffer設備文件，device_create_file定義在linux/device.h中*/
    ret = device_create_file(&pdev->dev, &dev_attr_debug);
    if (ret)
    {
        dev_err(&pdev->dev, "failed to add debug attribute\n");
    }

    return 0;

/*以下是上面錯誤處理的跳轉點*/
err_nomem:
    release_resource(fbvar->lcd_mem);
    kfree(fbvar->lcd_mem);

err_nomap:
    iounmap(fbvar->lcd_base);

err_noclk:
    clk_disable(fbvar->lcd_clock);
    clk_put(fbvar->lcd_clock);

err_noirq:
    free_irq(fbvar->lcd_irq_no, fbvar);

err_nofb:
    platform_set_drvdata(pdev, NULL);
    framebuffer_release(fbinfo);

err_video_nomem:
    my2440fb_unmap_video_memory(fbinfo);

    return ret;
}

/*LCD中斷服務程序*/
static irqreturn_t lcd_fb_irq(int irq, void *dev_id)
{
    struct my2440fb_var    *fbvar = dev_id;
    void __iomem *lcd_irq_base;
    unsigned long lcdirq;

    /*LCD中斷掛起寄存器基地址*/
    lcd_irq_base = fbvar->lcd_base + S3C2410_LCDINTBASE;

    /*讀取LCD中斷掛起寄存器的值*/
    lcdirq = readl(lcd_irq_base + S3C24XX_LCDINTPND);

    /*判斷是否爲中斷掛起狀態*/
    if(lcdirq & S3C2410_LCDINT_FRSYNC)
    {
        /*填充調色板*/
        if (fbvar->palette_ready)
        {
            my2440fb_write_palette(fbvar);
        }

        /*設置幀已插入中斷請求*/
        writel(S3C2410_LCDINT_FRSYNC, lcd_irq_base + S3C24XX_LCDINTPND);
        writel(S3C2410_LCDINT_FRSYNC, lcd_irq_base + S3C24XX_LCDSRCPND);
    }

    return IRQ_HANDLED;
}

/*填充調色板*/
static void my2440fb_write_palette(struct my2440fb_var *fbvar)
{
    unsigned int i;
    void __iomem *regs = fbvar->lcd_base;

    fbvar->palette_ready = 0;

    for (i = 0; i < 256; i++)
    {
        unsigned long ent = fbvar->palette_buffer[i];

        if (ent == PALETTE_BUFF_CLEAR)
        {
            continue;
        }

        writel(ent, regs + S3C2410_TFTPAL(i));

        if (readw(regs + S3C2410_TFTPAL(i)) == ent)
        {
            fbvar->palette_buffer[i] = PALETTE_BUFF_CLEAR;
        }
        else
        {
            fbvar->palette_ready = 1;
        }
    }
}

/*LCD各寄存器進行初始化*/
static int my2440fb_init_registers(struct fb_info *fbinfo)
{
    unsigned long flags;
    void __iomem *tpal;
    void __iomem *lpcsel;

    /*從lcd_fb_probe探測函數設置的私有變量結構體中再獲得LCD相關信息的數據*/
    struct my2440fb_var    *fbvar = fbinfo->par;
    struct s3c2410fb_mach_info *mach_info = fbvar->dev->platform_data;

    /*獲得臨時調色板寄存器基地址，S3C2410_TPAL宏定義在mach-s3c2410/include/mach/regs-lcd.h中。
    注意對於lpcsel這是一個針對三星TFT屏的一個專用寄存器，如果用的不是三星的TFT屏應該不用管它。*/
    tpal = fbvar->lcd_base + S3C2410_TPAL;
    lpcsel = fbvar->lcd_base + S3C2410_LPCSEL;

    /*在修改下面寄存器值之前先屏蔽中斷，將中斷狀態保存到flags中*/
    local_irq_save(flags);

    /*這裏就是在上一篇章中講到的把IO端口C和D配置成LCD模式*/
    modify_gpio(S3C2410_GPCUP, mach_info->gpcup, mach_info->gpcup_mask);
    modify_gpio(S3C2410_GPCCON, mach_info->gpccon, mach_info->gpccon_mask);
    modify_gpio(S3C2410_GPDUP, mach_info->gpdup, mach_info->gpdup_mask);
    modify_gpio(S3C2410_GPDCON, mach_info->gpdcon, mach_info->gpdcon_mask);

    /*恢復被屏蔽的中斷*/
    local_irq_restore(flags);

    writel(0x00, tpal);/*臨時調色板寄存器使能禁止*/
    writel(mach_info->lpcsel, lpcsel);/*在上一篇中講到過，它是三星TFT屏的一個寄存器，這裏可以不管*/

    return 0;
}

/*該函數實現修改GPIO端口的值，注意第三個參數mask的作用是將要設置的寄存器值先清零*/
static inline void modify_gpio(void __iomem *reg, unsigned long set, unsigned long mask)
{
    unsigned long tmp;

    tmp = readl(reg) & ~mask;
    writel(tmp | set, reg);
}

/*檢查fb_info中的可變參數*/
static int my2440fb_check_var(struct fb_info *fbinfo)
{
    unsigned i;

    /*從lcd_fb_probe探測函數設置的平臺數據中再獲得LCD相關信息的數據*/
    struct fb_var_screeninfo *var = &fbinfo->var;/*fb_info中的可變參數*/
    struct my2440fb_var    *fbvar = fbinfo->par;/*在lcd_fb_probe探測函數中設置的私有結構體數據*/
    struct s3c2410fb_mach_info *mach_info = fbvar->dev->platform_data;/*LCD的配置結構體數據，這個配置結構體的賦值在上一篇章的"3. 幀緩衝設備作爲平臺設備"中*/

    struct s3c2410fb_display *display = NULL;
    struct s3c2410fb_display *default_display = mach_info->displays + mach_info->default_display;
    int type = default_display->type;/*LCD的類型，看上一篇章的"3. 幀緩衝設備作爲平臺設備"中的type賦值是TFT類型*/

    /*驗證X/Y解析度*/
    if (var->yres == default_display->yres &&
        var->xres == default_display->xres &&
        var->bits_per_pixel == default_display->bpp)
    {
        display = default_display;
    }
    else
    {
        for (i = 0; i < mach_info->num_displays; i++)
        {
            if (type == mach_info->displays[i].type &&
             var->yres == mach_info->displays[i].yres &&
             var->xres == mach_info->displays[i].xres &&
             var->bits_per_pixel == mach_info->displays[i].bpp)
            {
                display = mach_info->displays + i;
                break;
            }
        }
    }

    if (!display)
    {
        return -EINVAL;
    }

    /*配置LCD配置寄存器1中的5-6位(配置成TFT類型)和配置LCD配置寄存器5*/
    fbvar->regs.lcdcon1 = display->type;
    fbvar->regs.lcdcon5 = display->lcdcon5;

    /* 設置屏幕的虛擬解析像素和高度寬度 */
    var->xres_virtual = display->xres;
    var->yres_virtual = display->yres;
    var->height = display->height;
    var->width = display->width;

    /* 設置時鐘像素，行、幀切換值，水平同步、垂直同步長度值 */
    var->pixclock = display->pixclock;
    var->left_margin = display->left_margin;
    var->right_margin = display->right_margin;
    var->upper_margin = display->upper_margin;
    var->lower_margin = display->lower_margin;
    var->vsync_len = display->vsync_len;
    var->hsync_len = display->hsync_len;

    /*設置透明度*/
    var->transp.offset = 0;
    var->transp.length = 0;

    /*根據色位模式(BPP)來設置可變參數中R、G、B的顏色位域。對於這些參數值的設置請參考CPU數據
    手冊中"顯示緩衝區與顯示點對應關係圖"，例如在上一篇章中我就畫出了8BPP和16BPP時的對應關係圖*/
    switch (var->bits_per_pixel)
    {
        case 1:
        case 2:
        case 4:
            var->red.offset  = 0;
            var->red.length  = var->bits_per_pixel;
            var->green       = var->red;
            var->blue        = var->red;
            break;
        case 8:/* 8 bpp 332 */
            if (display->type != S3C2410_LCDCON1_TFT)
            {
                var->red.length     = 3;
                var->red.offset     = 5;
                var->green.length   = 3;
                var->green.offset   = 2;
                var->blue.length    = 2;
                var->blue.offset    = 0;
            }else{
                var->red.offset     = 0;
                var->red.length     = 8;
                var->green          = var->red;
                var->blue           = var->red;
            }
            break;
        case 12:/* 12 bpp 444 */
            var->red.length         = 4;
            var->red.offset         = 8;
            var->green.length       = 4;
            var->green.offset       = 4;
            var->blue.length        = 4;
            var->blue.offset        = 0;
            break;
        case 16:/* 16 bpp */
            if (display->lcdcon5 & S3C2410_LCDCON5_FRM565)
            {
                /* 565 format */
                var->red.offset      = 11;
                var->green.offset    = 5;
                var->blue.offset     = 0;
                var->red.length      = 5;
                var->green.length    = 6;
                var->blue.length     = 5;
            } else {
                /* 5551 format */
                var->red.offset      = 11;
                var->green.offset    = 6;
                var->blue.offset     = 1;
                var->red.length      = 5;
                var->green.length    = 5;
                var->blue.length     = 5;
            }
            break;
        case 32:/* 24 bpp 888 and 8 dummy */
            var->red.length        = 8;
            var->red.offset        = 16;
            var->green.length      = 8;
            var->green.offset      = 8;
            var->blue.length       = 8;
            var->blue.offset       = 0;
            break;
    }

    return 0;
}

/*申請幀緩衝設備fb_info的顯示緩衝區空間*/
static int __init my2440fb_map_video_memory(struct fb_info *fbinfo)
{
    dma_addr_t map_dma;/*用於保存DMA緩衝區總線地址*/
    struct my2440fb_var    *fbvar = fbinfo->par;/*獲得在lcd_fb_probe探測函數中設置的私有結構體數據*/
    unsigned map_size = PAGE_ALIGN(fbinfo->fix.smem_len);/*獲得FrameBuffer緩存的大小, PAGE_ALIGN定義在mm.h中*/

    /*將分配的一個寫合併DMA緩存區設置爲LCD屏幕的虛擬地址(對於DMA請參考DMA相關知識)
    dma_alloc_writecombine定義在arch/arm/mm/dma-mapping.c中*/
    fbinfo->screen_base = dma_alloc_writecombine(fbvar->dev, map_size, &map_dma, GFP_KERNEL);

    if (fbinfo->screen_base)
    {
        /*設置這片DMA緩存區的內容爲空*/
        memset(fbinfo->screen_base, 0x00, map_size);

        /*將DMA緩衝區總線地址設成fb_info不可變參數中framebuffer緩存的開始位置*/
        fbinfo->fix.smem_start = map_dma;
    }

    return fbinfo->screen_base ? 0 : -ENOMEM;
}

/*釋放幀緩衝設備fb_info的顯示緩衝區空間*/
static inline void my2440fb_unmap_video_memory(struct fb_info *fbinfo)
{
    struct my2440fb_var    *fbvar = fbinfo->par;
    unsigned map_size = PAGE_ALIGN(fbinfo->fix.smem_len);

    /*跟申請DMA的地方想對應*/
    dma_free_writecombine(fbvar->dev, map_size, fbinfo->screen_base, fbinfo->fix.smem_start);
}


/*LCD FrameBuffer設備移除的實現，注意這裏使用一個__devexit宏，和lcd_fb_probe接口函數相對應。
  在Linux內核中，使用了大量不同的宏來標記具有不同作用的函數和數據結構，這些宏在include/linux/init.h
  頭文件中定義，編譯器通過這些宏可以把代碼優化放到合適的內存位置，以減少內存佔用和提高內核效率。
  __devinit、__devexit就是這些宏之一，在probe()和remove()函數中應該使用__devinit和__devexit宏。
  又當remove()函數使用了__devexit宏時，則在驅動結構體中一定要使用__devexit_p宏來引用remove()，
  所以在第①步中就用__devexit_p來引用lcd_fb_remove接口函數。*/
static int __devexit lcd_fb_remove(struct platform_device *pdev)
{
    struct fb_info *fbinfo = platform_get_drvdata(pdev);
    struct my2440fb_var    *fbvar = fbinfo->par;

    /*從系統中註銷幀緩衝設備*/
    unregister_framebuffer(fbinfo);

    /*停止LCD控制器的工作*/
    my2440fb_lcd_enable(fbvar, 0);

    /*延遲一段時間，因爲停止LCD控制器需要一點時間 */
    msleep(1);

    /*釋放幀緩衝設備fb_info的顯示緩衝區空間*/
    my2440fb_unmap_video_memory(fbinfo);

    /*將LCD平臺數據清空和釋放fb_info空間資源*/
    platform_set_drvdata(pdev, NULL);
    framebuffer_release(fbinfo);

    /*釋放中斷資源*/
    free_irq(fbvar->lcd_irq_no, fbvar);

    /*釋放時鐘資源*/
    if (fbvar->lcd_clock)
    {
        clk_disable(fbvar->lcd_clock);
        clk_put(fbvar->lcd_clock);
        fbvar->lcd_clock = NULL;
    }

    /*釋放LCD IO空間映射的虛擬內存空間*/
    iounmap(fbvar->lcd_base);

    /*釋放申請的LCD IO端口所佔用的IO空間*/
    release_resource(fbvar->lcd_mem);
    kfree(fbvar->lcd_mem);

    return 0;
}

/*停止LCD控制器的工作*/
static void my2440fb_lcd_enable(struct my2440fb_var *fbvar, int enable)
{
    unsigned long flags;

    /*在修改下面寄存器值之前先屏蔽中斷，將中斷狀態保存到flags中*/
    local_irq_save(flags);

    if (enable)
    {
        fbvar->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID;
    }
    else
    {
        fbvar->regs.lcdcon1 &= ~S3C2410_LCDCON1_ENVID;
    }

    writel(fbvar->regs.lcdcon1, fbvar->lcd_base + S3C2410_LCDCON1);

    /*恢復被屏蔽的中斷*/
    local_irq_restore(flags);
}

/*對LCD FrameBuffer平臺設備驅動電源管理的支持,CONFIG_PM這個宏定義在內核中*/
#ifdef CONFIG_PM
/*當配置內核時選上電源管理，則平臺設備的驅動就支持掛起和恢復功能*/
static int lcd_fb_suspend(struct platform_device *pdev, pm_message_t state)
{
    /*掛起LCD設備，注意這裏掛起LCD時並沒有保存LCD控制器的各種狀態，所以在恢復後LCD不會繼續顯示掛起前的內容
     若要繼續顯示掛起前的內容，則要在這裏保存LCD控制器的各種狀態，這裏就不講這個了，以後講到電源管理再講*/
    struct fb_info *fbinfo = platform_get_drvdata(pdev);
    struct my2440fb_var    *fbvar = fbinfo->par;

    /*停止LCD控制器的工作*/
    my2440fb_lcd_enable(fbvar, 0);

    msleep(1);

    /*停止時鐘*/
    clk_disable(fbvar->lcd_clock);

    return 0;
}

static int lcd_fb_resume(struct platform_device *pdev)
{
    /*恢復掛起的LCD設備*/
    struct fb_info *fbinfo = platform_get_drvdata(pdev);
    struct my2440fb_var    *fbvar = fbinfo->par;

    /*開啓時鐘*/
    clk_enable(fbvar->lcd_clock);

    /*初始化LCD控制器之前要延遲一段時間*/
    msleep(1);

    /*恢復時重新初始化LCD各寄存器*/
    my2440fb_init_registers(fbinfo);

    /*重新激活fb_info中所有的參數配置，該函數定義在第③步中再講*/
    my2440fb_activate_var(fbinfo);

    /*正與掛起時講到的那樣，因爲沒保存掛起時LCD控制器的各種狀態，
    所以恢復後就讓LCD顯示空白，該函數定義也在第③步中再講*/
    my2440fb_blank(FB_BLANK_UNBLANK, fbinfo);

    return 0;
}
#else
/*如果配置內核時沒選上電源管理,則平臺設備的驅動就不支持掛起和恢復功能,這兩個函數也就無需實現了*/
#define lcd_fb_suspend    NULL
#define lcd_fb_resume    NULL
#endif

③、幀緩衝設備驅動對底層硬件操作的函數接口實現(即：my2440fb_ops的實現)：

/*Framebuffer底層硬件操作各接口函數*/
static struct fb_ops my2440fb_ops =
{
    .owner          = THIS_MODULE,
    .fb_check_var   = my2440fb_check_var,/*第②步中已實現*/
    .fb_set_par     = my2440fb_set_par,/*設置fb_info中的參數，主要是LCD的顯示模式*/
    .fb_blank       = my2440fb_blank,/*顯示空白(即：LCD開關控制)*/
    .fb_setcolreg   = my2440fb_setcolreg,/*設置顏色表*/
    /*以下三個函數是可選的，主要是提供fb_console的支持，在內核中已經實現，這裏直接調用即可*/
    .fb_fillrect    = cfb_fillrect,/*定義在drivers/video/cfbfillrect.c中*/
    .fb_copyarea    = cfb_copyarea,/*定義在drivers/video/cfbcopyarea.c中*/
    .fb_imageblit   = cfb_imageblit,/*定義在drivers/video/cfbimgblt.c中*/
};

/*設置fb_info中的參數，這裏根據用戶設置的可變參數var調整固定參數fix*/
static int my2440fb_set_par(struct fb_info *fbinfo)
{
    /*獲得fb_info中的可變參數*/
    struct fb_var_screeninfo *var = &fbinfo->var;

    /*判斷可變參數中的色位模式，根據色位模式來設置色彩模式*/
    switch (var->bits_per_pixel)
    {
        case 32:
        case 16:
        case 12:/*12BPP時，設置爲真彩色(分成紅、綠、藍三基色)*/
            fbinfo->fix.visual = FB_VISUAL_TRUECOLOR;
            break;
        case 1:/*1BPP時，設置爲黑白色(分黑、白兩種色，FB_VISUAL_MONO01代表黑，FB_VISUAL_MONO10代表白)*/
            fbinfo->fix.visual = FB_VISUAL_MONO01;
            break;
        default:/*默認設置爲僞彩色，採用索引顏色顯示*/
            fbinfo->fix.visual = FB_VISUAL_PSEUDOCOLOR;
            break;
    }

    /*設置fb_info中固定參數中一行的字節數，公式：1行字節數=(1行像素個數*每像素位數BPP)/8 */
    fbinfo->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8;

    /*修改以上參數後，重新激活fb_info中的參數配置(即：使修改後的參數在硬件上生效)*/
    my2440fb_activate_var(fbinfo);

    return 0;
}

/*重新激活fb_info中的參數配置*/
static void my2440fb_activate_var(struct fb_info *fbinfo)
{
    /*獲得結構體變量*/
    struct my2440fb_var *fbvar = fbinfo->par;
    void __iomem *regs = fbvar->lcd_base;

    /*獲得fb_info可變參數*/
    struct fb_var_screeninfo *var = &fbinfo->var;

    /*計算LCD控制寄存器1中的CLKVAL值, 根據數據手冊中該寄存器的描述，計算公式如下：
    * STN屏：VCLK = HCLK / (CLKVAL * 2), CLKVAL要求>= 2
    * TFT屏：VCLK = HCLK / [(CLKVAL + 1) * 2], CLKVAL要求>= 0*/
    int clkdiv = my2440fb_calc_pixclk(fbvar, var->pixclock) / 2;

    /*獲得屏幕的類型*/
    int type = fbvar->regs.lcdcon1 & S3C2410_LCDCON1_TFT;

    if (type == S3C2410_LCDCON1_TFT)
    {
        /*根據數據手冊按照TFT屏的要求配置LCD控制寄存器1-5*/
        my2440fb_config_tft_lcd_regs(fbinfo, &fbvar->regs);

        --clkdiv;

        if (clkdiv < 0)
        {
            clkdiv = 0;
        }
    }
    else
    {
        /*根據數據手冊按照STN屏的要求配置LCD控制寄存器1-5*/
        my2440fb_config_stn_lcd_regs(fbinfo, &fbvar->regs);

        if (clkdiv < 2)
        {
            clkdiv = 2;
        }
    }

    /*設置計算的LCD控制寄存器1中的CLKVAL值*/
    fbvar->regs.lcdcon1 |= S3C2410_LCDCON1_CLKVAL(clkdiv);

    /*將各參數值寫入LCD控制寄存器1-5中*/
    writel(fbvar->regs.lcdcon1 & ~S3C2410_LCDCON1_ENVID, regs + S3C2410_LCDCON1);
    writel(fbvar->regs.lcdcon2, regs + S3C2410_LCDCON2);
    writel(fbvar->regs.lcdcon3, regs + S3C2410_LCDCON3);
    writel(fbvar->regs.lcdcon4, regs + S3C2410_LCDCON4);
    writel(fbvar->regs.lcdcon5, regs + S3C2410_LCDCON5);

    /*配置幀緩衝起始地址寄存器1-3*/
    my2440fb_set_lcdaddr(fbinfo);

    fbvar->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID,
    writel(fbvar->regs.lcdcon1, regs + S3C2410_LCDCON1);
}

/*計算LCD控制寄存器1中的CLKVAL值*/
static unsigned int my2440fb_calc_pixclk(struct my2440fb_var *fbvar, unsigned long pixclk)
{
    /*獲得LCD的時鐘*/
    unsigned long clk = clk_get_rate(fbvar->lcd_clock);

    /* 像素時鐘單位是皮秒，而時鐘的單位是赫茲，所以計算公式爲：
     * Hz -> picoseconds is / 10^-12
     */
    unsigned long long div = (unsigned long long)clk * pixclk;

    div >>= 12;            /* div / 2^12 */
    do_div(div, 625 * 625UL * 625); /* div / 5^12, do_div宏定義在asm/div64.h中*/

    return div;
}

/*根據數據手冊按照TFT屏的要求配置LCD控制寄存器1-5*/
static void my2440fb_config_tft_lcd_regs(const struct fb_info *fbinfo, struct s3c2410fb_hw *regs)
{
    const struct my2440fb_var *fbvar = fbinfo->par;
    const struct fb_var_screeninfo *var = &fbinfo->var;

    /*根據色位模式設置LCD控制寄存器1和5，參考數據手冊*/
    switch (var->bits_per_pixel)
    {
        case 1:/*1BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_TFT1BPP;
            break;
        case 2:/*2BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_TFT2BPP;
            break;
        case 4:/*4BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_TFT4BPP;
            break;
        case 8:/*8BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_TFT8BPP;
            regs->lcdcon5 |= S3C2410_LCDCON5_BSWP | S3C2410_LCDCON5_FRM565;
            regs->lcdcon5 &= ~S3C2410_LCDCON5_HWSWP;
            break;
        case 16:/*16BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_TFT16BPP;
            regs->lcdcon5 &= ~S3C2410_LCDCON5_BSWP;
            regs->lcdcon5 |= S3C2410_LCDCON5_HWSWP;
            break;
        case 32:/*32BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_TFT24BPP;
            regs->lcdcon5 &= ~(S3C2410_LCDCON5_BSWP | S3C2410_LCDCON5_HWSWP | S3C2410_LCDCON5_BPP24BL);
            break;
        default:/*無效的BPP*/
            dev_err(fbvar->dev, "invalid bpp %d\n", var->bits_per_pixel);
    }

    /*設置LCD配置寄存器2、3、4*/
    regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1) |
            S3C2410_LCDCON2_VBPD(var->upper_margin - 1) |
            S3C2410_LCDCON2_VFPD(var->lower_margin - 1) |
            S3C2410_LCDCON2_VSPW(var->vsync_len - 1);

    regs->lcdcon3 = S3C2410_LCDCON3_HBPD(var->right_margin - 1) |
            S3C2410_LCDCON3_HFPD(var->left_margin - 1) |
            S3C2410_LCDCON3_HOZVAL(var->xres - 1);

    regs->lcdcon4 = S3C2410_LCDCON4_HSPW(var->hsync_len - 1);
}

/*根據數據手冊按照STN屏的要求配置LCD控制寄存器1-5*/
static void my2440fb_config_stn_lcd_regs(const struct fb_info *fbinfo, struct s3c2410fb_hw *regs)
{
    const struct my2440fb_var    *fbvar = fbinfo->par;
    const struct fb_var_screeninfo *var = &fbinfo->var;

    int type = regs->lcdcon1 & ~S3C2410_LCDCON1_TFT;
    int hs = var->xres >> 2;
    unsigned wdly = (var->left_margin >> 4) - 1;
    unsigned wlh = (var->hsync_len >> 4) - 1;

    if (type != S3C2410_LCDCON1_STN4)
    {
        hs >>= 1;
    }

    /*根據色位模式設置LCD控制寄存器1，參考數據手冊*/
    switch (var->bits_per_pixel)
    {
        case 1:/*1BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_STN1BPP;
            break;
        case 2:/*2BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_STN2GREY;
            break;
        case 4:/*4BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_STN4GREY;
            break;
        case 8:/*8BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_STN8BPP;
            hs *= 3;
            break;
        case 12:/*12BPP*/
            regs->lcdcon1 |= S3C2410_LCDCON1_STN12BPP;
            hs *= 3;
            break;
        default:/*無效的BPP*/
            dev_err(fbvar->dev, "invalid bpp %d\n", var->bits_per_pixel);
    }
    
    /*設置LCD配置寄存器2、3、4, 參考數據手冊*/
    if (wdly > 3) wdly = 3;
    if (wlh > 3) wlh = 3;
    regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1);

    regs->lcdcon3 = S3C2410_LCDCON3_WDLY(wdly) |
            S3C2410_LCDCON3_LINEBLANK(var->right_margin / 8) |
            S3C2410_LCDCON3_HOZVAL(hs - 1);

    regs->lcdcon4 = S3C2410_LCDCON4_WLH(wlh);
}

/*配置幀緩衝起始地址寄存器1-3，參考數據手冊*/
static void my2440fb_set_lcdaddr(struct fb_info *fbinfo)
{
    unsigned long saddr1, saddr2, saddr3;
    struct my2440fb_var *fbvar = fbinfo->par;
    void __iomem *regs = fbvar->lcd_base;

    saddr1 = fbinfo->fix.smem_start >> 1;
    saddr2 = fbinfo->fix.smem_start;
    saddr2 += fbinfo->fix.line_length * fbinfo->var.yres;
    saddr2 >>= 1;
    saddr3 = S3C2410_OFFSIZE(0) | S3C2410_PAGEWIDTH((fbinfo->fix.line_length / 2) & 0x3ff);

    writel(saddr1, regs + S3C2410_LCDSADDR1);
    writel(saddr2, regs + S3C2410_LCDSADDR2);
    writel(saddr3, regs + S3C2410_LCDSADDR3);
}

/*顯示空白，blank mode有5種模式，定義在fb.h中，是一個枚舉*/
static int my2440fb_blank(int blank_mode, struct fb_info *fbinfo)
{
    struct my2440fb_var *fbvar = fbinfo->par;
    void __iomem *regs = fbvar->lcd_base;

    /*根據顯示空白的模式來設置LCD是開啓還是停止*/
    if (blank_mode == FB_BLANK_POWERDOWN)
    {
        my2440fb_lcd_enable(fbvar, 0);/*在第②步中定義*/
    }
    else
    {
        my2440fb_lcd_enable(fbvar, 1);/*在第②步中定義*/
    }

    /*根據顯示空白的模式來控制臨時調色板寄存器*/
    if (blank_mode == FB_BLANK_UNBLANK)
    {
        /*臨時調色板寄存器無效*/
        writel(0x0, regs + S3C2410_TPAL);
    }
    else
    {
        /*臨時調色板寄存器有效*/
        writel(S3C2410_TPAL_EN, regs + S3C2410_TPAL);
    }

    return 0;
}

/*設置顏色表*/
static int my2440fb_setcolreg(unsigned regno,unsigned red,unsigned green,unsigned blue,unsigned transp,struct fb_info *fbinfo)
{
    unsigned int val;
    struct my2440fb_var *fbvar = fbinfo->par;
    void __iomem *regs = fbvar->lcd_base;

    switch (fbinfo->fix.visual)
    {
        case FB_VISUAL_TRUECOLOR:
            /*真彩色*/
            if (regno < 16)
            {
                u32 *pal = fbinfo->pseudo_palette;

                val = chan_to_field(red, &fbinfo->var.red);
                val |= chan_to_field(green, &fbinfo->var.green);
                val |= chan_to_field(blue, &fbinfo->var.blue);

                pal[regno] = val;
            }
            break;
        case FB_VISUAL_PSEUDOCOLOR:
            /*僞彩色*/
            if (regno < 256)
            {
                val = (red >> 0) & 0xf800;
                val |= (green >> 5) & 0x07e0;
                val |= (blue >> 11) & 0x001f;

                writel(val, regs + S3C2410_TFTPAL(regno));

                /*修改調色板*/
                schedule_palette_update(fbvar, regno, val);
            }
            break;
        default:
            return 1;
    }

    return 0;
}

static inline unsigned int chan_to_field(unsigned int chan, struct fb_bitfield *bf)
{
    chan &= 0xffff;
    chan >>= 16 - bf->length;
    return chan << bf->offset;
}

/*修改調色板*/
static void schedule_palette_update(struct my2440fb_var    *fbvar, unsigned int regno, unsigned int val)
{
    unsigned long flags;
    unsigned long irqen;

    /*LCD中斷掛起寄存器基地址*/
    void __iomem *lcd_irq_base = fbvar->lcd_base + S3C2410_LCDINTBASE;

    /*在修改中斷寄存器值之前先屏蔽中斷，將中斷狀態保存到flags中*/
    local_irq_save(flags);

    fbvar->palette_buffer[regno] = val;

    /*判斷調色板是否準備就像*/
    if (!fbvar->palette_ready)
    {
        fbvar->palette_ready = 1;

        /*使能中斷屏蔽寄存器*/
        irqen = readl(lcd_irq_base + S3C24XX_LCDINTMSK);
        irqen &= ~S3C2410_LCDINT_FRSYNC;
        writel(irqen, lcd_irq_base + S3C24XX_LCDINTMSK);
    }

    /*恢復被屏蔽的中斷*/
    local_irq_restore(flags);
}