LCD驱动程序

缺乏、安全感 2021-12-21 09:34 346阅读 0赞

学习目标：熟悉TFT LCD的概念，分层驱动工作原理和程序编写。

一、LCD 概念

1.  显示器数据组织格式

1）一幅图像成为一帧，每帧由多行组成，每行由多个像素组成。每个像素的颜色由若干位表示，对于256色LCD，每个像素由8位表示，称为8BPP。

2）显示器呈Z字行的路线进行扫描显示，使用HSYNC、VSYNC控制扫描和跳转的路径；

![1562038-20190110112805062-294795944.png][]

2、操作过程

1）设置LCD的HSYNC、VSYNC\\VCLK等信号的参数，并将帧内存的地址告诉LCD控制器，塔克自动的发起DMA传输，从帧内存中得到图像数据，出现在数据总线VD\[23:0\]上。我们只需要将显示的图像数据写入帧内存中即可。

2）图像数据的存储：

例如：由三原色组建的256色（8BPP）显示模式，使用8位数据表示一个像素的颜色。但特殊的是，这8位数据用于表示在调色板中的索引值。这里的调色板使用256\*16的内存，即使用16BPP的显示格式来表示对应各个索引值的颜色。因此，最终在LCD显示的仍为16BPP的数据。

内存数据和像素对应的关系为：

![1562038-20190110114451408-377522406.png][]

其中，P1、P2...为一个个的像素。

像素在调色板中的数据存放模式16BPP分为两种格式：5：6：5和5：5：5：1.即：

![1562038-20190110115119504-973589328.png][]

二、LCD驱动

1、帧缓冲设备

frambuffer设备层是对显示设备的一种抽象。其中，帧缓冲是Linux为显示设备提供的一个接口，它把一些显示设备描述成一个缓冲区，允许应用程序通过FrameBuffer定义好的接口访问这些图形设备，从而不用去关心具体的硬件细节。对于帧缓冲设备而言，只要在显示缓冲区与显示点对应的区域写入颜色值，对应的颜色就会自动的在屏幕上显示。

2、LCD作为一种帧缓冲设备，也是一种标准的字符型设备，对应于文件系统下/dev/fb%d设备文件。

3、驱动结构

![1562038-20190110141158377-41092347.png][]

**首先分析一下driver/video/fbmem.c**

**1）进入\_\_init fbmem\_init（入口函数）**，主要创建了字符设备“fb”和类，利用cat 命令查看（cat /proc/devices）,可看到该目录下的fb，主设备号为29。由于还没有注册LCD驱动，所以没有设备节点，

1 static int __init fbmem_init(void)
     2 {
     3     create_proc_read_entry("fb", 0, NULL, fbmem_read_proc, NULL);
     4     //创建字符设备"fb"
     5     if (register_chrdev(FB_MAJOR,"fb",&fb_fops))
     6         printk("unable to get major %d for fb devs\n", FB_MAJOR);
     7 
     8     fb_class = class_create(THIS_MODULE, "graphics"); //创建类graphics"
     9     if (IS_ERR(fb_class)) {
    10         printk(KERN_WARNING "Unable to create fb class; errno = %ld\n", PTR_ERR(fb_class));
    11         fb_class = NULL;
    12     }
    13     return 0;
    14 }

**2）fb\_fops结构体及open函数**

1 static const struct file_operations fb_fops = {
     2     .owner =    THIS_MODULE,
     3     .read  =    fb_read,
     4     .write =    fb_write,
     5     .ioctl =    fb_ioctl,
     6 #ifdef CONFIG_COMPAT
     7     .compat_ioctl = fb_compat_ioctl,
     8 #endif
     9     .mmap =       fb_mmap,
    10     .open =       fb_open,
    11     .release =    fb_release,
    12 #ifdef HAVE_ARCH_FB_UNMAPPED_AREA
    13     .get_unmapped_area = get_fb_unmapped_area,
    14 #endif
    15 #ifdef CONFIG_FB_DEFERRED_IO
    16     .fsync =    fb_deferred_io_fsync,
    17 #endif
    18 };

\-->fb\_open函数:

1 static int fb_open(struct inode *inode, struct file *file)
     2 {
     3     int fbidx = iminor(inode); //取出设备次设备号  4     struct fb_info *info;    //定义一个fb_info结构体  5     int res = 0;
     6 
     7     if (fbidx >= FB_MAX)
     8         return -ENODEV;
     9 #ifdef CONFIG_KMOD
    10     if (!(info = registered_fb[fbidx])) // 在次设备里面得到fb_info结构信息(lcd的驱动信息)赋值给info 
    11         try_to_load(fbidx);
    12 #endif /* CONFIG_KMOD */
    13     if (!(info = registered_fb[fbidx])) 
    14         return -ENODEV;
    15     if (!try_module_get(info->fbops->owner))
    16         return -ENODEV;
    17     file->private_data = info;
    18     if (info->fbops->fb_open) {    //如果该设备info结构体有open函数，就执行registered_fb[fbidx]->fbops->fb_open 
    19         res = info->fbops->fb_open(info,1);
    20         if (res)
    21             module_put(info->fbops->owner);
    22     }
    23     return res;
    24 }

由于fb设备(帧缓冲设备)主设备号固定，不同设备以次设备号进行区分，执行该设备open函数时，最终指向的是对应设备的open函数。

**接下来看一下fb\_read函数：**

1 static ssize_t
     2 fb_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
     3 {
     4     unsigned long p = *ppos;
     5     struct inode *inode = file->f_path.dentry->d_inode;
     6     int fbidx = iminor(inode);          //取出设备次设备号  7     struct fb_info *info = registered_fb[fbidx];  //定义并获取设备的fb_info结构体  8     u32 *buffer, *dst;
     9     u32 __iomem *src;
    10     int c, i, cnt = 0, err = 0;
    11     unsigned long total_size;
    12 
    13     if (!info || ! info->screen_base)
    14         return -ENODEV;
    15 
    16     if (info->state != FBINFO_STATE_RUNNING)
    17         return -EPERM;
    18 
    19     if (info->fbops->fb_read)
    20         return info->fbops->fb_read(info, buf, count, ppos); //如果该设备fb_info结构体有read函数，就执行registered_fb[fbidx]->fbops->fb_read 21     
    22     total_size = info->screen_size;
    23 
    24     if (total_size == 0)
    25         total_size = info->fix.smem_len;
    26 
    27     if (p >= total_size)
    28         return 0;
    29 
    30     if (count >= total_size)
    31         count = total_size;
    32 
    33     if (count + p > total_size)
    34         count = total_size - p;
    35 
    36     buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count,
    37              GFP_KERNEL);
    38     if (!buffer)
    39         return -ENOMEM;
    40 
    41     src = (u32 __iomem *) (info->screen_base + p);
    42 
    43     if (info->fbops->fb_sync)
    44         info->fbops->fb_sync(info);
    45 
    46     while (count) {
    47         c  = (count > PAGE_SIZE) ? PAGE_SIZE : count;
    48         dst = buffer;
    49         for (i = c >> 2; i--; )
    50             *dst++ = fb_readl(src++);
    51         if (c & 3) {
    52             u8 *dst8 = (u8 *) dst;
    53             u8 __iomem *src8 = (u8 __iomem *) src;
    54 
    55             for (i = c & 3; i--;)
    56                 *dst8++ = fb_readb(src8++);
    57 
    58             src = (u32 __iomem *) src8;
    59         }
    60 
    61         if (copy_to_user(buf, buffer, c)) {
    62             err = -EFAULT;
    63             break;
    64         }
    65         *ppos += c;
    66         buf += c;
    67         cnt += c;
    68         count -= c;
    69     }
    71     kfree(buffer);
    73     return (err) ? err : cnt;
    74 }

由以上程序可知，read的调用和open类似。都依赖于对应设备的fb\_info结构体info，在程序中是由registered\_fb\[fbidx\]数组获取的。  
**3）最后，看一下registered\_fb\[fbidx\]数组的定义，位于register\_framebuffer函数中。**

1 int register_framebuffer(struct fb_info *fb_info)
     2 {
     3     int i;
     4     struct fb_event event;
     5     struct fb_videomode mode;
     6 
     7     if (num_registered_fb == FB_MAX)
     8         return -ENXIO;
     9     num_registered_fb++;
    10     for (i = 0 ; i < FB_MAX; i++)
    11         if (!registered_fb[i])
    12             break;
    13     fb_info->node = i;
    14 
    15     fb_info->dev = device_create(fb_class, fb_info->device,MKDEV(FB_MAJOR, i), "fb%d", i);//创建设备节点，名称为fbi，主设备号为FB_MAJOR 29，次设备号为i 17     if (IS_ERR(fb_info->dev)) {
    18         /* Not fatal */
    19         printk(KERN_WARNING "Unable to create device for framebuffer %d; errno = %ld\n", i, PTR_ERR(fb_info->dev));
    20         fb_info->dev = NULL;
    21     } else
    22         fb_init_device(fb_info);
    23 
    24     if (fb_info->pixmap.addr == NULL) {
    25         fb_info->pixmap.addr = kmalloc(FBPIXMAPSIZE, GFP_KERNEL);
    26         if (fb_info->pixmap.addr) {
    27             fb_info->pixmap.size = FBPIXMAPSIZE;
    28             fb_info->pixmap.buf_align = 1;
    29             fb_info->pixmap.scan_align = 1;
    30             fb_info->pixmap.access_align = 32;
    31             fb_info->pixmap.flags = FB_PIXMAP_DEFAULT;
    32         }
    33     }    
    34     fb_info->pixmap.offset = 0;
    35 
    36     if (!fb_info->pixmap.blit_x)
    37         fb_info->pixmap.blit_x = ~(u32)0;
    38 
    39     if (!fb_info->pixmap.blit_y)
    40         fb_info->pixmap.blit_y = ~(u32)0;
    41 
    42     if (!fb_info->modelist.prev || !fb_info->modelist.next)
    43         INIT_LIST_HEAD(&fb_info->modelist);
    44 
    45     fb_var_to_videomode(&mode, &fb_info->var);
    46     fb_add_videomode(&mode, &fb_info->modelist);
    47    registered_fb[i] = fb_info; //赋值到registered_fb[i]数组中 48 
    49     event.info = fb_info;
    50     fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
    51     return 0;
    52 }

**接下来看一下fb硬件驱动程序，以/drivers/video/s3c2410fb.c为例。**

**1）驱动入口**

1 static struct platform_driver s3c2410fb_driver = {
     2     .probe        = s3c2410fb_probe,
     3     .remove        = s3c2410fb_remove,
     4     .suspend    = s3c2410fb_suspend,
     5     .resume        = s3c2410fb_resume,
     6     .driver        = {
     7         .name    = "s3c2410-lcd",
     8         .owner    = THIS_MODULE,
     9     },
    10 };
    11 
    12 int __devinit s3c2410fb_init(void)
    13 {
    14     return platform_driver_register(&s3c2410fb_driver);
    15 }
    16 
    17 static void __exit s3c2410fb_cleanup(void)
    18 {
    19     platform_driver_unregister(&s3c2410fb_driver);
    20 }

**2）当平台设备的驱动和设备匹配后，会直接调用prob函数。**

1 static int __init s3c2410fb_probe(struct platform_device *pdev)
      2 {
      3     struct s3c2410fb_info *info;
      4     struct fb_info       *fbinfo;
      5     struct s3c2410fb_hw *mregs;
      6     int ret;
      7     int irq;
      8     int i;
      9     u32 lcdcon1;
     10 
     11     mach_info = pdev->dev.platform_data;  //获取lcd设备信息  12     if (mach_info == NULL) {
     13         dev_err(&pdev->dev,"no platform data for lcd, cannot attach\n");
     14         return -EINVAL;
     15     }
     25     fbinfo = framebuffer_alloc(sizeof(struct s3c2410fb_info), &pdev->dev); //分配fb_info结构体  26     if (!fbinfo) {
     27         return -ENOMEM;
     28     }
    　　　　　//设置fb_info结构体
     31     info = fbinfo->par;
     32     info->fb = fbinfo;
     33     info->dev = &pdev->dev;
     34 
     35     platform_set_drvdata(pdev, fbinfo);
     37     dprintk("devinit\n");
     39     strcpy(fbinfo->fix.id, driver_name);
     41     memcpy(&info->regs, &mach_info->regs, sizeof(info->regs));
     43     /* Stop the video and unset ENVID if set */
     44     info->regs.lcdcon1 &= ~S3C2410_LCDCON1_ENVID;
     45     lcdcon1 = readl(S3C2410_LCDCON1);
     46     writel(lcdcon1 & ~S3C2410_LCDCON1_ENVID, S3C2410_LCDCON1);
     47 
     48     info->mach_info            = pdev->dev.platform_data;
     49 
     50     fbinfo->fix.type        = FB_TYPE_PACKED_PIXELS;
     51     fbinfo->fix.type_aux        = 0;
     52     fbinfo->fix.xpanstep        = 0;
     53     fbinfo->fix.ypanstep        = 0;
     54     fbinfo->fix.ywrapstep        = 0;
     55     fbinfo->fix.accel        = FB_ACCEL_NONE;
    
     64     fbinfo->fbops            = &s3c2410fb_ops;
     65     fbinfo->flags            = FBINFO_FLAG_DEFAULT;
     66     fbinfo->pseudo_palette      = &info->pseudo_pal;
     67  73 
     74     fbinfo->var.upper_margin    = S3C2410_LCDCON2_GET_VBPD(mregs->lcdcon2) + 1;
     75     fbinfo->var.lower_margin    = S3C2410_LCDCON2_GET_VFPD(mregs->lcdcon2) + 1;
     76     fbinfo->var.vsync_len        = S3C2410_LCDCON2_GET_VSPW(mregs->lcdcon2) + 1;
     77 
     78     fbinfo->var.left_margin        = S3C2410_LCDCON3_GET_HFPD(mregs->lcdcon3) + 1;
     79     fbinfo->var.right_margin    = S3C2410_LCDCON3_GET_HBPD(mregs->lcdcon3) + 1;
     80     fbinfo->var.hsync_len        = S3C2410_LCDCON4_GET_HSPW(mregs->lcdcon4) + 1;
     81  90     fbinfo->fix.smem_len        =    mach_info->xres.max *
     91                     mach_info->yres.max *
     92                     mach_info->bpp.max / 8;
     93 
     94     for (i = 0; i < 256; i++)
     95         info->palette_buffer[i] = PALETTE_BUFF_CLEAR;
     96 
     97     if (!request_mem_region((unsigned long)S3C24XX_VA_LCD, SZ_1M, "s3c2410-lcd")) {
     98         ret = -EBUSY;
     99         goto dealloc_fb;
    100     }
    103     dprintk("got LCD region\n");
    104   //硬件相关的操作，中断、时钟....
    105     ret = request_irq(irq, s3c2410fb_irq, IRQF_DISABLED, pdev->name, info);
    106     if (ret) {
    107         dev_err(&pdev->dev, "cannot get irq %d - err %d\n", irq, ret);
    108         ret = -EBUSY;
    109         goto release_mem;
    110     }
    111 
    112     info->clk = clk_get(NULL, "lcd");
    113     if (!info->clk || IS_ERR(info->clk)) {
    114         printk(KERN_ERR "failed to get lcd clock source\n");
    115         ret = -ENOENT;
    116         goto release_irq;
    117     }
    118 
    119     clk_enable(info->clk);
    120     dprintk("got and enabled clock\n");
    121 
    122     msleep(1);
    123 
    124     /* Initialize video memory */
    125     ret = s3c2410fb_map_video_memory(info);
    126     if (ret) {
    127         printk( KERN_ERR "Failed to allocate video RAM: %d\n", ret);
    128         ret = -ENOMEM;
    129         goto release_clock;
    130     }
    137     ret = register_framebuffer(fbinfo);//注册fb_info结构体 138     if (ret < 0) {
    139         printk(KERN_ERR "Failed to register framebuffer device: %d\n", ret);
    140         goto free_video_memory;
    141     }
    142 
    143     /* create device files */
    144     device_create_file(&pdev->dev, &dev_attr_debug);
    145 
    146     printk(KERN_INFO "fb%d: %s frame buffer device\n",
    147         fbinfo->node, fbinfo->fix.id);
    148 
    149     return 0;
    150 
    151 free_video_memory:
    152     s3c2410fb_unmap_video_memory(info);
    153 release_clock:
    154     clk_disable(info->clk);
    155     clk_put(info->clk);
    156 release_irq:
    157     free_irq(irq,info);
    158 release_mem:
    159      release_mem_region((unsigned long)S3C24XX_VA_LCD, S3C24XX_SZ_LCD);
    160 dealloc_fb:
    161     framebuffer_release(fbinfo);
    162     return ret;
    163 }

**小结：**

根据驱动结构和程序源码分析可知，lcd驱动程序需要完成以下几部分：

1）分配一个fb\_info结构体：由函数framebuffer\_alloc() 完成 ;

2）设置fb\_info结构体;

3）注册fb\_info：register\_framebuffer();

4）硬件相关的操作

转载于:https://www.cnblogs.com/lxl-lennie/p/10248889.html

[1562038-20190110112805062-294795944.png]: /images/20211221/c48d7deb9dcb4ebb9ab5eea5f1a9764e.png
[1562038-20190110114451408-377522406.png]: /images/20211221/b1952675cfd7407ea9683889af60e7c3.png
[1562038-20190110115119504-973589328.png]: /images/20211221/f1b6a7769469438a823dc882caac3ae2.png
[1562038-20190110141158377-41092347.png]: /images/20211221/ae1ce7c2e6894f6794544fc2daa447ef.png