首先我們來回歸下怎麽寫一個字符設備驅動程序，下面以linux設備中的混雜設備為例
static int __init misc_init(void)
{
int err;
#ifdef CONFIG_PROC_FS
proc_create("misc", 0, NULL, &misc_proc_fops);
#endif
misc_class = class_create(THIS_MODULE, "misc");
err = PTR_ERR(misc_class);
if (IS_ERR(misc_class))
goto fail_remove;
err = -EIO;
if (register_chrdev(MISC_MAJOR,"misc",&misc_fops))
goto fail_printk;
misc_class->devnode = misc_devnode;
return 0;
fail_printk:
printk("unable to get major %d for misc devices\n", MISC_MAJOR);
class_destroy(misc_class);
fail_remove:
remove_proc_entry("misc", NULL);
return err;
}
上面的主要步驟為申請一個主次設備號，構建一個file_opertiaon,並用register_chrdev註冊，構建類，並可以在類下創建設備節點。現在來看看內核是怎麽實現lcd驅動程序呢？
static int __init
fbmem_init(void)
{
proc_create("fb", 0, NULL, &fb_proc_fops);//與proc文件系統有關
if (register_chrdev(FB_MAJOR,"fb",&fb_fops))//註冊字符設備
printk("unable to get major %d for fb devs\n", FB_MAJOR);
fb_class = class_create(THIS_MODULE, "graphics");//創建類，為以後創建設備節點做準備
if (IS_ERR(fb_class)) {
printk(KERN_WARNING "Unable to create fb class; errno = %ld\n", PTR_ERR(fb_class));
fb_class = NULL;
}
return 0;
}
從上面也可以看出，內核對於lcd驅動程序也是滿足一個主設備號為29的字符設備，那麽用戶空間訪問通過fb_fops結構體的成員函數會操作到LCD控制器硬件寄存器。下面來看看linux幀緩沖設備驅動的主要結構圖
framebuffer機制模仿顯卡的功能，將顯卡硬件結構抽象為一系列的數據結構，可以通過framebuffer的讀寫直接對顯存進行操作。framebuffer一個字符設備，主設備號，對應於/dev/fb0...32的設備文件。對於用戶程序而言，與字符設備並沒有什麽區別，用戶具有把其看成一塊內存，既可以讀也可以寫。那麽下面來看看
在這個圖中占主導地位的fb_info結構體
struct fb_info {
atomic_t count;
int node; //子設備號
int flags;
struct mutex lock; //互斥鎖
struct mutex mm_lock; /* Lock for fb_mmap and smem_* fields */
struct fb_var_screeninfo var; //當前緩沖區的可變參數
struct fb_fix_screeninfo fix; //固定參數
struct fb_monspecs monspecs; //當前顯示器標誌
struct work_struct queue; //幀緩沖事件隊列
struct fb_pixmap pixmap; //圖像硬件mapper
struct fb_pixmap sprite; //光標硬件mapper
struct fb_cmap cmap; //當前的調色板
struct list_head modelist; /* mode list */
struct fb_videomode *mode; //當前的視頻模式
#ifdef CONFIG_FB_BACKLIGHT
/* assigned backlight device *//支持lcd背光的設置
/* set before framebuffer registration,
remove after unregister */
struct backlight_device *bl_dev;
/* Backlight level curve */
struct mutex bl_curve_mutex;
u8 bl_curve[FB_BACKLIGHT_LEVELS];
#endif
#ifdef CONFIG_FB_DEFERRED_IO
struct delayed_work deferred_work;
struct fb_deferred_io *fbdefio;
#endif
struct fb_ops *fbops; //幀緩沖操作函數集
struct device *device; //父設備
struct device *dev; /* This is this fb device */
int class_flag; /* private sysfs flags */
#ifdef CONFIG_FB_TILEBLITTING
struct fb_tile_ops *tileops; /* Tile Blitting */
#endif
char __iomem *screen_base; //虛擬基地址
unsigned long screen_size; /* Amount of ioremapped VRAM or 0 */
void *pseudo_palette; /* Fake palette of 16 colors */
#define FBINFO_STATE_RUNNING 0
#define FBINFO_STATE_SUSPENDED 1
u32 state; /* Hardware state i.e suspend */
void *fbcon_par; /* fbcon use-only private area */
/* From here on everything is device dependent */
void *par;
/* we need the PCI or similar aperture base/size not
smem_start/size as smem_start may just be an object
allocated inside the aperture so may not actually overlap */
struct apertures_struct {
unsigned int count;
struct aperture {
resource_size_t base;
resource_size_t size;
} ranges[0];
} *apertures;
};
fb_ops結構體用來實現對幀緩沖的操作，這些函數需要我們自行編寫的。
struct fb_ops {
/* open/release and usage marking */
struct module *owner;
int (*fb_open)(struct fb_info *info, int user);
int (*fb_release)(struct fb_info *info, int user);//打開和釋放
/* For framebuffers with strange non linear layouts or that do not
* work with normal memory mapped access
*/
ssize_t (*fb_read)(struct fb_info *info, char __user *buf,
size_t count, loff_t *ppos);
ssize_t (*fb_write)(struct fb_info *info, const char __user *buf,
size_t count, loff_t *ppos);
/* checks var and eventually tweaks it to something supported,
* DO NOT MODIFY PAR *///檢測可變參數，並調整到支持的值
int (*fb_check_var)(struct fb_var_screeninfo *var, struct fb_info *info);
/* set the video mode according to info->var */
int (*fb_set_par)(struct fb_info *info);//視頻設置模式
/* set color register */
int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green,
unsigned blue, unsigned transp, struct fb_info *info);//設置color寄存器
/* set color registers in batch */
int (*fb_setcmap)(struct fb_cmap *cmap, struct fb_info *info);//批量設置color寄存器，設備顏色表
/* blank display */
int (*fb_blank)(int blank, struct fb_info *info);//顯示空白
/* pan display */
int (*fb_pan_display)(struct fb_var_screeninfo *var, struct fb_info *info);
/* Draws a rectangle */
void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);//填充矩形
/* Copy data from area to another */
void (*fb_copyarea) (struct fb_info *info, const struct fb_copyarea *region);//數據復制
/* Draws a image to the display */
void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);//圖形填充
/* Draws cursor */
int (*fb_cursor) (struct fb_info *info, struct fb_cursor *cursor);//繪制光標
/* Rotates the display */
void (*fb_rotate)(struct fb_info *info, int angle);//旋轉顯示
/* wait for blit idle, optional */
int (*fb_sync)(struct fb_info *info);//等待blit空閑
/* perform fb specific ioctl (optional) */
int (*fb_ioctl)(struct fb_info *info, unsigned int cmd,
unsigned long arg);
/* Handle 32bit compat ioctl (optional) */
int (*fb_compat_ioctl)(struct fb_info *info, unsigned cmd,
unsigned long arg);
/* perform fb specific mmap */
int (*fb_mmap)(struct fb_info *info, struct vm_area_struct *vma);
/* get capability given var */
void (*fb_get_caps)(struct fb_info *info, struct fb_blit_caps *caps,
struct fb_var_screeninfo *var);
/* teardown any resources to do with this framebuffer */
void (*fb_destroy)(struct fb_info *info);
/* called at KDB enter and leave time to prepare the console */
int (*fb_debug_enter)(struct fb_info *info);
int (*fb_debug_leave)(struct fb_info *info);
};
內核中定義了一個struct fb_info *registered_fb[FB_MAX]來存放屏的相關信息，下面來看看幀緩沖設備fb_info結構體的註冊。
int
register_framebuffer(struct fb_info *fb_info)
{
int ret;
mutex_lock(®istration_lock);
ret = do_register_framebuffer(fb_info);
mutex_unlock(®istration_lock);
return ret;
}
static int do_register_framebuffer(struct fb_info *fb_info)
{
int i;
struct fb_event event;
struct fb_videomode mode;
if (fb_check_foreignness(fb_info))
return -ENOSYS;
do_remove_conflicting_framebuffers(fb_info->apertures, fb_info->fix.id,
fb_is_primary_device(fb_info));
if (num_registered_fb == FB_MAX)
return -ENXIO;
num_registered_fb++;
for (i = 0 ; i < FB_MAX; i++)
if (!registered_fb[i])
break;
fb_info->node = i;
atomic_set(&fb_info->count, 1);
mutex_init(&fb_info->lock);
mutex_init(&fb_info->mm_lock);
fb_info->dev = device_create(fb_class, fb_info->device,
MKDEV(FB_MAJOR, i), NULL, "fb%d", i);//創建設備節點
if (IS_ERR(fb_info->dev)) {
/* Not fatal */
printk(KERN_WARNING "Unable to create device for framebuffer %d; errno = %ld\n", i, PTR_ERR(fb_info->dev));
fb_info->dev = NULL;
} else
fb_init_device(fb_info);//初始化fb的屬性文件
if (fb_info->pixmap.addr == NULL) {
fb_info->pixmap.addr = kmalloc(FBPIXMAPSIZE, GFP_KERNEL);
if (fb_info->pixmap.addr) {
fb_info->pixmap.size = FBPIXMAPSIZE;
fb_info->pixmap.buf_align = 1;
fb_info->pixmap.scan_align = 1;
fb_info->pixmap.access_align = 32;
fb_info->pixmap.flags = FB_PIXMAP_DEFAULT;
}
}
fb_info->pixmap.offset = 0;
if (!fb_info->pixmap.blit_x)
fb_info->pixmap.blit_x = ~(u32)0;
if (!fb_info->pixmap.blit_y)
fb_info->pixmap.blit_y = ~(u32)0;
if (!fb_info->modelist.prev || !fb_info->modelist.next)
INIT_LIST_HEAD(&fb_info->modelist);
fb_var_to_videomode(&mode, &fb_info->var);
fb_add_videomode(&mode, &fb_info->modelist);
registered_fb[i] = fb_info;
event.info = fb_info;
if (!lock_fb_info(fb_info))
return -ENODEV;
fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
unlock_fb_info(fb_info);
return 0;
}
這個函數主要是創建設備節點，初始化fb的屬性文件等一些初始化,下面來看看幀緩沖區驅動核心層的層次結構圖：
那麽從上面的圖可以總結出怎麽寫一個lcd的驅動程序的步驟
1.分配一個fb_info的結構體
2.設置
3.註冊register_framebuffer
4.硬件相關的初始化
上面將了一些framebuffer幀緩沖的有關的，那麽我們具體看看內核怎麽去實現lcd的驅動。
int __init s3c2410fb_init(void)
{
int ret = platform_driver_register(&s3c2410fb_driver);
if (ret == 0)
ret = platform_driver_register(&s3c2412fb_driver);
return ret;
}
static void __exit s3c2410fb_cleanup(void)
{
platform_driver_unregister(&s3c2410fb_driver);
platform_driver_unregister(&s3c2412fb_driver);
}
module_init(s3c2410fb_init);
module_exit(s3c2410fb_cleanup);
lcd驅動掛在platform總線上，註冊了一個s3c2410fb_driver的驅動，由總線驅動設備模型中，當註冊一個設備或者驅動的時候，會調用總線的match函數，而platform的match函數是匹配設備和驅動的名字
static struct platform_driver s3c2410fb_driver = {
.probe = s3c2410fb_probe,
.remove = __devexit_p(s3c2410fb_remove),
.suspend = s3c2410fb_suspend,
.resume = s3c2410fb_resume,
.driver = {
.name = "s3c2410-lcd",
.owner = THIS_MODULE,
},
};
struct platform_device s3c_device_lcd = {
.name = "s3c2410-lcd",
.id = -1,
.num_resources = ARRAY_SIZE(s3c_lcd_resource),
.resource = s3c_lcd_resource,
.dev = {
.dma_mask = &samsung_device_dma_mask,
.coherent_dma_mask = DMA_BIT_MASK(32),
}
};
static struct resource s3c_lcd_resource[] = {
[0] = DEFINE_RES_MEM(S3C24XX_PA_LCD, S3C24XX_SZ_LCD),//內存
[1] = DEFINE_RES_IRQ(IRQ_LCD),//中斷號
};
驅動與設備匹配會，會調用probe函數
static int __devinit s3c24xxfb_probe(struct platform_device *pdev,
enum s3c_drv_type drv_type)
{
struct s3c2410fb_info *info;
struct s3c2410fb_display *display;
struct fb_info *fbinfo;
struct s3c2410fb_mach_info *mach_info;
struct resource *res;
int ret;
int irq;
int i;
int size;
u32 lcdcon1;
mach_info = pdev->dev.platform_data;
if (mach_info == NULL) {
dev_err(&pdev->dev,
"no platform data for lcd, cannot attach\n");
return -EINVAL;
}
if (mach_info->default_display >= mach_info->num_displays) {
dev_err(&pdev->dev, "default is %d but only %d displays\n",
mach_info->default_display, mach_info->num_displays);
return -EINVAL;
}
display = mach_info->displays + mach_info->default_display;
irq = platform_get_irq(pdev, 0);//獲取中斷號
if (irq < 0) {
dev_err(&pdev->dev, "no irq for device\n");
return -ENOENT;
}
fbinfo = framebuffer_alloc(sizeof(struct s3c2410fb_info), &pdev->dev);//分配一個fb_info結構體
if (!fbinfo)
return -ENOMEM;
platform_set_drvdata(pdev, fbinfo);
info = fbinfo->par;
info->dev = &pdev->dev;
info->drv_type = drv_type;
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);//獲取內存地址
if (res == NULL) {
dev_err(&pdev->dev, "failed to get memory registers\n");
ret = -ENXIO;
goto dealloc_fb;
}
size = resource_size(res);
info->mem = request_mem_region(res->start, size, pdev->name);
if (info->mem == NULL) {
dev_err(&pdev->dev, "failed to get memory region\n");
ret = -ENOENT;
goto dealloc_fb;
}
info->io = ioremap(res->start, size);//io map
if (info->io == NULL) {
dev_err(&pdev->dev, "ioremap() of registers failed\n");
ret = -ENXIO;
goto release_mem;
}
info->irq_base = info->io + ((drv_type == DRV_S3C2412) ? S3C2412_LCDINTBASE : S3C2410_LCDINTBASE);
dprintk("devinit\n");
strcpy(fbinfo->fix.id, driver_name);
/* Stop the video */
lcdcon1 = readl(info->io + S3C2410_LCDCON1);
writel(lcdcon1 & ~S3C2410_LCDCON1_ENVID, info->io + S3C2410_LCDCON1);
//設置fbinfo結構體
fbinfo->fix.type = FB_TYPE_PACKED_PIXELS;
fbinfo->fix.type_aux = 0;
fbinfo->fix.xpanstep = 0;
fbinfo->fix.ypanstep = 0;
fbinfo->fix.ywrapstep = 0;
fbinfo->fix.accel = FB_ACCEL_NONE;
fbinfo->var.nonstd = 0;
fbinfo->var.activate = FB_ACTIVATE_NOW;
fbinfo->var.accel_flags = 0;
fbinfo->var.vmode = FB_VMODE_NONINTERLACED;
fbinfo->fbops = &s3c2410fb_ops;
fbinfo->flags = FBINFO_FLAG_DEFAULT;
fbinfo->pseudo_palette = &info->pseudo_pal;
for (i = 0; i < 256; i++)
info->palette_buffer[i] = PALETTE_BUFF_CLEAR;
ret = request_irq(irq, s3c2410fb_irq, 0, pdev->name, info);
if (ret) {
dev_err(&pdev->dev, "cannot get irq %d - err %d\n", irq, ret);
ret = -EBUSY;
goto release_regs;
}
info->clk = clk_get(NULL, "lcd");
if (IS_ERR(info->clk)) {
printk(KERN_ERR "failed to get lcd clock source\n");
ret = PTR_ERR(info->clk);
goto release_irq;
}
clk_enable(info->clk);
dprintk("got and enabled clock\n");
msleep(1);
info->clk_rate = clk_get_rate(info->clk);
/* find maximum required memory size for display */
for (i = 0; i < mach_info->num_displays; i++) {
unsigned long smem_len = mach_info->displays[i].xres;
smem_len *= mach_info->displays[i].yres;
smem_len *= mach_info->displays[i].bpp;
smem_len >>= 3;
if (fbinfo->fix.smem_len < smem_len)
fbinfo->fix.smem_len = smem_len;
}
/* Initialize video memory */
ret = s3c2410fb_map_video_memory(fbinfo);
if (ret) {
printk(KERN_ERR "Failed to allocate video RAM: %d\n", ret);
ret = -ENOMEM;
goto release_clock;
}
dprintk("got video memory\n");
fbinfo->var.xres = display->xres;
fbinfo->var.yres = display->yres;
fbinfo->var.bits_per_pixel = display->bpp;
s3c2410fb_init_registers(fbinfo);
s3c2410fb_check_var(&fbinfo->var, fbinfo);
ret = s3c2410fb_cpufreq_register(info);
if (ret < 0) {
dev_err(&pdev->dev, "Failed to register cpufreq\n");
goto free_video_memory;
}
ret = register_framebuffer(fbinfo);
if (ret < 0) {
printk(KERN_ERR "Failed to register framebuffer device: %d\n",
ret);
goto free_cpufreq;
}
/* create device files */
ret = device_create_file(&pdev->dev, &dev_attr_debug);
if (ret) {
printk(KERN_ERR "failed to add debug attribute\n");
}
printk(KERN_INFO "fb%d: %s frame buffer device\n",
fbinfo->node, fbinfo->fix.id);
return 0;
free_cpufreq:
s3c2410fb_cpufreq_deregister(info);
free_video_memory:
s3c2410fb_unmap_video_memory(fbinfo);
release_clock:
clk_disable(info->clk);
clk_put(info->clk);
release_irq:
free_irq(irq, info);
release_regs:
iounmap(info->io);
release_mem:
release_mem_region(res->start, size);
dealloc_fb:
platform_set_drvdata(pdev, NULL);
framebuffer_release(fbinfo);
return ret;
}
上面的一些步驟基本與總結的一個lcd的驅動程序的步驟相同,下面來看看用戶空間怎麽去訪問
app：read()-->kernel調用fbmem.c中的fb_read()，其他的接口類似。
static ssize_t
fb_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
unsigned long p = *ppos;
struct fb_info *info = file_fb_info(file);//獲取次設備號，根據次設備號從registered_fb數組中拿
u8 *buffer, *dst; //到對應的fb_info
u8 __iomem *src;
int c, cnt = 0, err = 0;
unsigned long total_size;
if (!info || ! info->screen_base)
return -ENODEV;
if (info->state != FBINFO_STATE_RUNNING)
return -EPERM;
if (info->fbops->fb_read)//調用read函數
return info->fbops->fb_read(info, buf, count, ppos);
total_size = info->screen_size;
if (total_size == 0)
total_size = info->fix.smem_len;
if (p >= total_size)
return 0;
if (count >= total_size)
count = total_size;
if (count + p > total_size)
count = total_size - p;
buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count,
GFP_KERNEL);
if (!buffer)
return -ENOMEM;
src = (u8 __iomem *) (info->screen_base + p);//獲得幀緩沖的起始地址+偏移量
if (info->fbops->fb_sync)
info->fbops->fb_sync(info);
while (count) { //拷貝數據
c = (count > PAGE_SIZE) ? PAGE_SIZE : count;
dst = buffer;
fb_memcpy_fromfb(dst, src, c);
dst += c;
src += c;
if (copy_to_user(buf, buffer, c)) {//提交給應用層。
err = -EFAULT;
break;
}
*ppos += c;
buf += c;
cnt += c;
count -= c;
}
kfree(buffer);
return (err) ? err : cnt;
}
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