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之前移植LCD的时候，一切正常，但是当尝试把log输出到lcd的时候，总是会出现10分钟黑屏，无论如何都唤不醒

通过打log，最终定位到s3c_fb_blank这个函数。

static int s3c_fb_blank(int blank_mode, struct fb_info *info)
{
    struct s3c_fb_win *win = info->par;
    struct s3c_fb *sfb = win->parent;
    unsigned int index = win->index;
    u32 wincon;
printk("lj:s3c_fb_blank:blank mode:%d\n",blank_mode);
    dev_dbg(sfb->dev, "blank mode %d\n", blank_mode);

    pm_runtime_get_sync(sfb->dev);

    wincon = readl(sfb->regs + sfb->variant.wincon + (index * 4));

    switch (blank_mode) {
    case FB_BLANK_POWERDOWN:
        wincon &= ~WINCONx_ENWIN;
        sfb->enabled &= ~(1 << index);
        /* fall through to FB_BLANK_NORMAL */

    case FB_BLANK_NORMAL:
        /* disable the DMA and display 0x0 (black) */
        shadow_protect_win(win, 1);
        dump_stack();
        writel(WINxMAP_MAP | WINxMAP_MAP_COLOUR(0x00),//liujia  disable the black screen
               sfb->regs + sfb->variant.winmap + (index * 4));
        shadow_protect_win(win, 0);
        break;

    case FB_BLANK_UNBLANK:
        shadow_protect_win(win, 1);
        writel(0x0, sfb->regs + sfb->variant.winmap + (index * 4));
        shadow_protect_win(win, 0);
        wincon |= WINCONx_ENWIN;
        sfb->enabled |= (1 << index);
        break;

    case FB_BLANK_VSYNC_SUSPEND:
    case FB_BLANK_HSYNC_SUSPEND:
    default:
        pm_runtime_put_sync(sfb->dev);
        return 1;
    }

    shadow_protect_win(win, 1);
    writel(wincon, sfb->regs + sfb->variant.wincon + (index * 4));
    shadow_protect_win(win, 0);

    /* Check the enabled state to see if we need to be running the
     * main LCD interface, as if there are no active windows then
     * it is highly likely that we also do not need to output
     * anything.
     */

    /* We could do something like the following code, but the current
     * system of using framebuffer events means that we cannot make
     * the distinction between just window 0 being inactive and all
     * the windows being down.
     *
     * s3c_fb_enable(sfb, sfb->enabled ? 1 : 0);
    */

    /* we're stuck with this until we can do something about overriding
     * the power control using the blanking event for a single fb.
     */
    if (index == sfb->pdata->default_win) {
        shadow_protect_win(win, 1);
        s3c_fb_enable(sfb, blank_mode != FB_BLANK_POWERDOWN ? 1 : 0);
        shadow_protect_win(win, 0);
    }

    pm_runtime_put_sync(sfb->dev);
    return 0;
}

问题就出在

writel(WINxMAP_MAP | WINxMAP_MAP_COLOUR(0x00),//liujia  disable the black screen

      sfb->regs + sfb->variant.winmap + (index * 4));

发现执行到这里，LCD就黑屏了。

查数据手册发现：

这个寄存器的意思是，当MAPCOLEN_F使能的时候，他会把LCD显示成MAPCOLOR设置成颜色，关闭LCD的DMA功能，然后Framebuffer就不能刷新LCD了。

这也许就是FB_BLANK_NORMAL，这个的功能吧，把LCD一直刷成某个颜色。

参考http://blog.csdn.net/zanget/article/details/6569743这个 大侠的博客，

加入dump_stack

case FB_BLANK_NORMAL:
    /* disable the DMA and display 0x0 (black) */
    shadow_protect_win(win, 1);
    dump_stack();
    writel(WINxMAP_MAP | WINxMAP_MAP_COLOUR(0x00),//liujia  disable the black screen
           sfb->regs + sfb->variant.winmap + (index * 4));
    shadow_protect_win(win, 0);
    break;

log：

<7>[   61.285759] lj:s3c_fb_blank:blank mode:1
<7>[   61.285772] lj:shadow_protect_win:1
<7>[   61.285816] [<80013120>] (unwind_backtrace+0x0/0xec) from [<801af0b8>] (s3c_fb_blank+0x84/0x180)
<7>[   61.285835] [<801af0b8>] (s3c_fb_blank+0x84/0x180) from [<801a2bcc>] (fb_blank+0x3c/0x68)
<7>[   61.285852] [<801a2bcc>] (fb_blank+0x3c/0x68) from [<801a9690>] (fbcon_blank+0x118/0x260)
<7>[   61.285875] [<801a9690>] (fbcon_blank+0x118/0x260) from [<801c7594>] (do_blank_screen+0x1b8/0x258)
<7>[   61.285892] [<801c7594>] (do_blank_screen+0x1b8/0x258) from [<801c884c>] (console_callback+0xe4/0x114)
<7>[   61.285909] [<801c884c>] (console_callback+0xe4/0x114) from [<8002e12c>] (process_one_work+0x1e8/0x318)
<7>[   61.285927] [<8002e12c>] (process_one_work+0x1e8/0x318) from [<800301c0>] (worker_thread+0x1b4/0x2b4)
<7>[   61.285947] [<800301c0>] (worker_thread+0x1b4/0x2b4) from [<80033438>] (kthread+0x88/0x94)
<7>[   61.285969] [<80033438>] (kthread+0x88/0x94) from [<8000ec20>] (kernel_thread_exit+0x0/0x8)
<7>[   61.285979] lj:shadow_protect_win:0
<7>[   61.285984] lj:shadow_protect_win:1
<7>[   61.285990] lj:shadow_protect_win:0
<7>[   61.285995] lj:shadow_protect_win:1
<7>[   61.286001] lj:s3c_fb_set_par
<7>[   61.286005] lj:shadow_protect_win:0

找到了调用关系

console_callback--->do_blank_screen--->fb_blank--->s3c_fb_blank.

按照http://blog.csdn.net/zanget/article/details/6569743修改方法

将vt.c   179行

static int blankinterval = 10*60；

修改为

static int blankinterval = 0；

这样就不会出现黑屏的现象了。