Frame buffer分析 - fbmem.c【转】

转自：http://www.cnblogs.com/armlinux/archive/2012/03/01/2396753.html

45 struct fb_info *registered_fb[FB_MAX] __read_mostly;

这个是全局的变量，通过这个全局变量，在系统内可以随时获取需要的fb_info，具体的获取方法是

通过比对 registered_fb[i]->fix.id来确定需要的fb_info, 示例代码如下

for (i = 0; i < num_registered_fb; i++) {
        char *idstr = registered_fb[i]->fix.id;
        if (strcmp(idstr, "DISP3 FG") == 0) {
            fbi = registered_fb[i];
            break;
        }
    }

63 int fb_get_color_depth(struct fb_var_screeninfo *var,
  64                struct fb_fix_screeninfo *fix)
  65 {  
  66     int depth = 0;
  67
  68     if (fix->visual == FB_VISUAL_MONO01 ||
  69         fix->visual == FB_VISUAL_MONO10)
  70         depth = 1;
  71     else {
  72         if (var->green.length == var->blue.length &&
  73             var->green.length == var->red.length &&
  74             var->green.offset == var->blue.offset &&
  75             var->green.offset == var->red.offset)
  76             depth = var->green.length;
  77         else
  78             depth = var->green.length + var->red.length +
  79                 var->blue.length;
  80     }
  81
  82     return depth;
  83 }

该函数获取颜色深度，很简单啊，对于单色深度为1，否则深度为red blue green三个分量的和

129 char* fb_get_buffer_offset(struct fb_info *info, struct fb_pixmap *buf, u32 size)
130 {
131     u32 align = buf->buf_align - 1, offset;
132     char *addr = buf->addr;
133
134     /* If IO mapped, we need to sync before access, no sharing of
135      * the pixmap is done
136      */
137     if (buf->flags & FB_PIXMAP_IO) {
138         if (info->fbops->fb_sync && (buf->flags & FB_PIXMAP_SYNC))
139             info->fbops->fb_sync(info);
140         return addr;
141     }
142
143     /* See if we fit in the remaining pixmap space */
144     offset = buf->offset + align;
145     offset &= ~align;
146     if (offset + size > buf->size) {
147         /* We do not fit. In order to be able to re-use the buffer,
148          * we must ensure no asynchronous DMA'ing or whatever operation
149          * is in progress, we sync for that.
150          */
151         if (info->fbops->fb_sync && (buf->flags & FB_PIXMAP_SYNC))
152             info->fbops->fb_sync(info);
153         offset = 0;
154     }
155     buf->offset = offset + size;
156     addr += offset;
157
158     return addr;
159 }

这个函数看似简单，就是获取@buf中符合@size大小的空闲位置

146行 如果剩余空间小于需要的大小，那么fb_sync后就可以使用@buffer的所有空间

这个函数看起来总是怪挂的，因为fb_sync的参数没有涉及到@buf, 所以fb_sync跟@buf有毛关系呀

虽然调用fb_get_buffer_offset时的@info和@buf的关系是@info->pixmap == @buf,那为毛不只传一个参数？

168 static void fb_set_logocmap(struct fb_info *info,
169                    const struct linux_logo *logo)
170 {
171     struct fb_cmap palette_cmap;
172     u16 palette_green[16];
173     u16 palette_blue[16];
174     u16 palette_red[16];
175     int i, j, n;
176     const unsigned char *clut = logo->clut;
177
178     palette_cmap.start = 0;
179     palette_cmap.len = 16;
180     palette_cmap.red = palette_red;
181     palette_cmap.green = palette_green;
182     palette_cmap.blue = palette_blue;#define FB_VISUAL_MONO01        0   /* Monochr. 1=Black 0=White */
183     palette_cmap.transp = NULL;
184
185     for (i = 0; i < logo->clutsize; i += n) {
186         n = logo->clutsize - i;
187         /* palette_cmap provides space for only 16 colors at once */
188         if (n > 16)
189             n = 16;
190         palette_cmap.start = 32 + i;
191         palette_cmap.len = n;
192         for (j = 0; j < n; ++j) {
193             palette_cmap.red[j] = clut[0] << 8 | clut[0];
194             palette_cmap.green[j] = clut[1] << 8 | clut[1];
195             palette_cmap.blue[j] = clut[2] << 8 | clut[2];
196             clut += 3;
197         }
198         fb_set_cmap(&palette_cmap, info);
199     }
200 }

在介绍这个函数前，先了解下调色板

在linux系统中，支持以下几种色彩模式

#define FB_VISUAL_MONO01   0

#define FB_VISUAL_MONO10        1   /* Monochr. 1=White 0=Black */
#define FB_VISUAL_TRUECOLOR     2   /* True color   */
#define FB_VISUAL_PSEUDOCOLOR       3   /* Pseudo color (like atari) */
#define FB_VISUAL_DIRECTCOLOR       4   /* Direct color */

FB_VISUAL_MONO10 FB_VISUAL_MONO01 每个像素为黑或者白

FB_VISUAL_TRUECOLOR 真彩色，分为红蓝绿三基色

FB_VISUAL_PSEUDOCOLOR 伪彩色，采用索引颜色显示，需要根据颜色index查找colormap，找到相应的颜色值

FB_VISUAL_DIRECTORCOLOR 每个像素颜色也是由红绿蓝三种颜色组成，不过每个颜色都是索引值，需要查表

注意FB_VISUAL_PSEUDOCOLOR和FB_VISUAL_DIRECTORCOLOR都是使用颜色所以，需要查表

看下fb_cmap结构，这个结构定义了颜色表(color map)

struct fb_cmap {
    __u32 start;            /* 第一个entry， 没看出start的作用 */
    __u32 len;          /* 每个颜色分量的长度 */
    __u16 *red;         /* 红色分量  */
    __u16 *green;
    __u16 *blue;
    __u16 *transp;          /* 透明度，可以为空 */

};

结构linux_logo 描述了一个linux logo的全部信息

struct linux_logo {
    int type;           /* one of LINUX_LOGO_*， logo的类型 */
    unsigned int width; /* logo的宽度*/
    unsigned int height; /* logo的高度*/
    unsigned int clutsize;      /* LINUX_LOGO_CLUT224 only， 颜色查找表的尺寸 */
    const unsigned char *clut;  /* LINUX_LOGO_CLUT224 only， 颜色查找表*/
    const unsigned char *data; /* logo 文件数据，对于LINUX_LOGO_CLUT224，data保存的是查找表的位置 */
};

回头来看 fb_set_logocmap， 这个函数写的非常的恶心，我从来没见过这么恶心的kernel代码，当然我也够贱，非要分析如此恶心的代码

这个函数是一个大循环，要用log->clut这个colormap去设置@info device 的colormap，每次最多处理16x3个颜色索引

190         palette_cmap.start = 32 + i;

这里加了个32，很讨厌这种数字写法，这里之所以选32是因为CLUT224这种格式的index值从32直到255，即我们在linux_logo->data中只能找到0值，以及32~255之间的值

198         fb_set_cmap(&palette_cmap, info);

这个函数会设置硬件调色板以及info->cmap

202 static void  fb_set_logo_truepalette(struct fb_info *info,
203                         const struct linux_logo *logo,
204                         u32 *palette)
205 {
206     static const unsigned char mask[] = { 0,0x80,0xc0,0xe0,0xf0,0xf8,0xfc,0xfe,0xff };
207     unsigned char redmask, greenmask, bluemask;
208     int redshift, greenshift, blueshift;
209     int i;
210     const unsigned char *clut = logo->clut;
211
212     /*
213      * We have to create a temporary palette since console palette is only
214      * 16 colors long.
215      */
216     /* Bug: Doesn't obey msb_right ... (who needs that?) */
217     redmask   = mask[info->var.red.length   < 8 ? info->var.red.length   : 8];
218     greenmask = mask[info->var.green.length < 8 ? info->var.green.length : 8];
219     bluemask  = mask[info->var.blue.length  < 8 ? info->var.blue.length  : 8];
220     redshift   = info->var.red.offset   - (8 - info->var.red.length);
221     greenshift = info->var.green.offset - (8 - info->var.green.length);
222     blueshift  = info->var.blue.offset  - (8 - info->var.blue.length);
223
224     for ( i = 0; i < logo->clutsize; i++) {
225         palette[i+32] = (safe_shift((clut[0] & redmask), redshift) |
226                  safe_shift((clut[1] & greenmask), greenshift) |
227                  safe_shift((clut[2] & bluemask), blueshift));
228         clut += 3;
229     }
230 }

这个函数为FB_VISUAL_PSEUDOCOLOR彩色模式的logo生成一个调色板，从32开始是因为CLUT224只支持32~255范围内的index值

232 static void fb_set_logo_directpalette(struct fb_info *info,
233                          const struct linux_logo *logo,
234                          u32 *palette)
235 {
236     int redshift, greenshift, blueshift;
237     int i;
238
239     redshift = info->var.red.offset;
240     greenshift = info->var.green.offset;
241     blueshift = info->var.blue.offset;
242
243     for (i = 32; i < 32 + logo->clutsize; i++)
244         palette[i] = i << redshift | i << greenshift | i << blueshift;
245 }

为FB_VISUAL_DIRECTCOLOR彩色模式生成一个调色板，只需生成32 ~ clutsize

247 static void fb_set_logo(struct fb_info *info,
248                    const struct linux_logo *logo, u8 *dst,
249                    int depth)
250 {
251     int i, j, k;
252     const u8 *src = logo->data;
253     u8 xor = (info->fix.visual == FB_VISUAL_MONO01) ? 0xff : 0;
254     u8 fg = 1, d;
255
256     switch (fb_get_color_depth(&info->var, &info->fix)) {
257     case 1:
258         fg = 1;
259         break;
260     case 2:
261         fg = 3;
262         break;
263     default:
264         fg = 7;
265         break;
266     }
267
268     if (info->fix.visual == FB_VISUAL_MONO01 ||
269         info->fix.visual == FB_VISUAL_MONO10)
270         fg = ~((u8) (0xfff << info->var.green.length));
271
272     switch (depth) {
273     case 4:
274         for (i = 0; i < logo->height; i++)
275             for (j = 0; j < logo->width; src++) {
276                 *dst++ = *src >> 4;
277                 j++;
278                 if (j < logo->width) {
279                     *dst++ = *src & 0x0f;
280                     j++;
281                 }
282             }
283         break;
284     case 1:
285         for (i = 0; i < logo->height; i++) {
286             for (j = 0; j < logo->width; src++) {
287                 d = *src ^ xor;
288                 for (k = 7; k >= 0; k--) {
289                     *dst++ = ((d >> k) & 1) ? fg : 0;
290                     j++;
291                 }
292             }
293         }
294         break;
295     }
296 }
297

linux_logo->data中保存的是logo的data数据，如果对于mono或者16

色的数据来说，linxu_logo->data内的每个字节保存的是多个像素点的数据，fb_set_logo这个函数根据颜色深度把linux_logo->data的数据转换到@dst中，@dst中的每个字节，代表这一个像素索引

参见源码注视就很好理解为什么要做转换了

298 /*
299  * Three (3) kinds of logo maps exist.  linux_logo_clut224 (>16 colors),
300  * linux_logo_vga16 (16 colors) and linux_logo_mono (2 colors).  Depending on
301  * the visual format and color depth of the framebuffer, the DAC, the
302  * pseudo_palette, and the logo data will be adjusted accordingly.
303  *
304  * Case 1 - linux_logo_clut224:
305  * Color exceeds the number of console colors (16), thus we set the hardware DAC
306  * using fb_set_cmap() appropriately.  The "needs_cmapreset"  flag will be set.
307  *
308  * For visuals that require color info from the pseudo_palette, we also construct
309  * one for temporary use. The "needs_directpalette" or "needs_truepalette" flags
  310  * will be set.
311  *
312  * Case 2 - linux_logo_vga16:
313  * The number of colors just matches the console colors, thus there is no need
314  * to set the DAC or the pseudo_palette.  However, the bitmap is packed, ie,
315  * each byte contains color information for two pixels (upper and lower nibble).
316  * To be consistent with fb_imageblit() usage, we therefore separate the two
317  * nibbles into separate bytes. The "depth" flag will be set to 4.
318  *
319  * Case 3 - linux_logo_mono:
320  * This is similar with Case 2.  Each byte contains information for 8 pixels.
321  * We isolate each bit and expand each into a byte. The "depth" flag will
322  * be set to 1.

323  */
324 static struct logo_data {
325     int depth;
326     int needs_directpalette;
327     int needs_truepalette;
328     int needs_cmapreset;
329     const struct linux_logo *logo;
330 } fb_logo __read_mostly;
@depth是logo的深度

@logo是linux_logo数据

332 static void fb_rotate_logo_ud(const u8 *in, u8 *out, u32 width, u32 height)
333 {
334     u32 size = width * height, i;
335
336     out += size - 1;
337
338     for (i = size; i--; )
339         *out-- = *in++;
340 }
341
342 static void fb_rotate_logo_cw(const u8 *in, u8 *out, u32 width, u32 height)
343 {
344     int i, j, h = height - 1;
345
346     for (i = 0; i < height; i++)
347         for (j = 0; j < width; j++)
348                 out[height * j + h - i] = *in++;
349 }
350
351 static void fb_rotate_logo_ccw(const u8 *in, u8 *out, u32 width, u32 height)
352 {
353     int i, j, w = width - 1;
354
355     for (i = 0; i < height; i++)
356         for (j = 0; j < width; j++)
357             out[height * (w - j) + i] = *in++;
358 }

这几个函数再此验证了代码的恶心程度，没人知道ud, cw ccw是什么含义

393 static void fb_do_show_logo(struct fb_info *info, struct fb_image *image,
394                 int rotate, unsigned int num)
395 {
396     unsigned int x;
397
398     if (rotate == FB_ROTATE_UR) {
399         for (x = 0;
400              x < num && image->dx + image->width <= info->var.xres;
401              x++) {
402             info->fbops->fb_imageblit(info, image);
403             image->dx += image->width + 8;
404         }
405     } else if (rotate == FB_ROTATE_UD) {
406         for (x = 0; x < num && image->dx >= 0; x++) {
407             info->fbops->fb_imageblit(info, image);
408             image->dx -= image->width + 8;
409         }
410     } else if (rotate == FB_ROTATE_CW) {
411         for (x = 0;
412              x < num && image->dy + image->height <= info->var.yres;
413              x++) {
414             info->fbops->fb_imageblit(info, image);
415             image->dy += image->height + 8;
416         }
417     } else if (rotate == FB_ROTATE_CCW) {
418         for (x = 0; x < num && image->dy >= 0; x++) {
419             info->fbops->fb_imageblit(info, image);
420             image->dy -= image->height + 8;
421         }
422     }
423 }

显示@image内的logo数据， @rotate是旋转方式， @num没看懂社么意思阿

425 static int fb_show_logo_line(struct fb_info *info, int rotate,
426                  const struct linux_logo *logo, int y,
427                  unsigned int n)
428 {
429     u32 *palette = NULL, *saved_pseudo_palette = NULL;
430     unsigned char *logo_new = NULL, *logo_rotate = NULL;
431     struct fb_image image;
432
433     /* Return if the frame buffer is not mapped or suspended */
434     if (logo == NULL || info->state != FBINFO_STATE_RUNNING ||
435         info->flags & FBINFO_MODULE)
436         return 0;
437
438     image.depth = 8;
439     image.data = logo->data;
440
441     if (fb_logo.needs_cmapreset)
442         fb_set_logocmap(info, logo);
443
444     if (fb_logo.needs_truepalette ||
445         fb_logo.needs_directpalette) {
446         palette = kmalloc(256 * 4, GFP_KERNEL);
447         if (palette == NULL)
448             return 0;
449
450         if (fb_logo.needs_truepalette)
451             fb_set_logo_truepalette(info, logo, palette);
452         else
453             fb_set_logo_directpalette(info, logo, palette);
454
455         saved_pseudo_palette = info->pseudo_palette;
456         info->pseudo_palette = palette;
457     }
458
459     if (fb_logo.depth <= 4) {
460         logo_new = kmalloc(logo->width * logo->height, GFP_KERNEL);
461         if (logo_new == NULL) {
462             kfree(palette);
463             if (saved_pseudo_palette)
464                 info->pseudo_palette = saved_pseudo_palette;
465             return 0;
466         }
467         image.data = logo_new;
468         fb_set_logo(info, logo, logo_new, fb_logo.depth);
469     }

470
471     image.dx = 0;
472     image.dy = y;
473     image.width = logo->width;
474     image.height = logo->height;
475
476     if (rotate) {
477         logo_rotate = kmalloc(logo->width *
478                       logo->height, GFP_KERNEL);
479         if (logo_rotate)
480             fb_rotate_logo(info, logo_rotate, &image, rotate);
481     }
482
483     fb_do_show_logo(info, &image, rotate, n);
484
485     kfree(palette);
486     if (saved_pseudo_palette != NULL)
487         info->pseudo_palette = saved_pseudo_palette;
488     kfree(logo_new);
489     kfree(logo_rotate);
490     return logo->height;
491 }

我无语了，这代码写的，为毛有个@y参数呀

503 void fb_append_extra_logo(const struct linux_logo *logo, unsigned int n)
504 {
505     if (!n || fb_logo_ex_num == FB_LOGO_EX_NUM_MAX)
506         return;
507
508     fb_logo_ex[fb_logo_ex_num].logo = logo;
509     fb_logo_ex[fb_logo_ex_num].n = n;
510     fb_logo_ex_num++;
511 }
这个函数把给定的logo设置到fb_logo_ex这个全局extend logo数组中， @n作用未知

513 static int fb_prepare_extra_logos(struct fb_info *info, unsigned int height,
514                   unsigned int yres)
515 {
516     unsigned int i;
517
518     /* FIXME: logo_ex supports only truecolor fb. */
519     if (info->fix.visual != FB_VISUAL_TRUECOLOR)
520         fb_logo_ex_num = 0;
521
522     for (i = 0; i < fb_logo_ex_num; i++) {
523         if (fb_logo_ex[i].logo->type != fb_logo.logo->type) {
524             fb_logo_ex[i].logo = NULL;
525             continue;
526         }
527         height += fb_logo_ex[i].logo->height;
528         if (height > yres) {
529             height -= fb_logo_ex[i].logo->height;
530             fb_logo_ex_num = i;
531             break;
532         }
533     }
534     return height;
535 }

这段代码写的相当不好，单独引入的fb_logo_ex_num极其恶劣

这段代码的意思也就是计算height，以及fb_logo_ex_num

height是logo和有效extend logo的高度和，fb_log_ex_num是有效extend logo的最大索引

537 static int fb_show_extra_logos(struct fb_info *info, int y, int rotate)
538 {
539     unsigned int i;
540
541     for (i = 0; i < fb_logo_ex_num; i++)
542         y += fb_show_logo_line(info, rotate,
543                        fb_logo_ex[i].logo, y, fb_logo_ex[i].n);
544
545     return y;
546 }

该函数显示保存在fb_logo_ex中的extend logo, @y表示这个extend logo要在屏幕显示的位置

565 int fb_prepare_logo(struct fb_info *info, int rotate)
566 {
567     int depth = fb_get_color_depth(&info->var, &info->fix);
568     unsigned int yres;
569
570     memset(&fb_logo, 0, sizeof(struct logo_data));
571
572     if (info->flags & FBINFO_MISC_TILEBLITTING ||
573         info->flags & FBINFO_MODULE)
574         return 0;
575
576     if (info->fix.visual == FB_VISUAL_DIRECTCOLOR) {
577         depth = info->var.blue.length;
578         if (info->var.red.length < depth)
579             depth = info->var.red.length;
580         if (info->var.green.length < depth)
581             depth = info->var.green.length;
582     }
583
584     if (info->fix.visual == FB_VISUAL_STATIC_PSEUDOCOLOR && depth > 4) {
585         /* assume console colormap */
586         depth = 4;
587     }
588
589     /* Return if no suitable logo was found */
590     fb_logo.logo = fb_find_logo(depth);
591
592     if (!fb_logo.logo) {
593         return 0;
594     }
595
596     if (rotate == FB_ROTATE_UR || rotate == FB_ROTATE_UD)
597         yres = info->var.yres;
598     else
599         yres = info->var.xres;
600
601     if (fb_logo.logo->height > yres) {
602         fb_logo.logo = NULL;
603         return 0;
604     }
605
606     /* What depth we asked for might be different from what we get */
607     if (fb_logo.logo->type == LINUX_LOGO_CLUT224)
608         fb_logo.depth = 8;
609     else if (fb_logo.logo->type == LINUX_LOGO_VGA16)
610         fb_logo.depth = 4;
611     else
612         fb_logo.depth = 1;
613
614
615     if (fb_logo.depth > 4 && depth > 4) {
616         switch (info->fix.visual) {
617         case FB_VISUAL_TRUECOLOR:
618             fb_logo.needs_truepalette = 1;
619             break;
620         case FB_VISUAL_DIRECTCOLOR:
621             fb_logo.needs_directpalette = 1;
622             fb_logo.needs_cmapreset = 1;
623             break;
624         case FB_VISUAL_PSEUDOCOLOR:
625             fb_logo.needs_cmapreset = 1;
626             break;
627         }
628     }
629
630     return fb_prepare_extra_logos(info, fb_logo.logo->height, yres);
631 }

到587行都是根据fb_info获取颜色depth

590根据depth获取合适的logo,  fb_find_logo看起来很简单，就是根据depth找到适合的logo

606~612 是根据获得的logo类型，计算logo的depth, 这可能和fb_find_logo传入的depth不一样

633 int fb_show_logo(struct fb_info *info, int rotate)
634 {
635     int y;
636
637     y = fb_show_logo_line(info, rotate, fb_logo.logo, 0,
638                   num_online_cpus());
639     y = fb_show_extra_logos(info, y, rotate);
640
641     return y;
642 }

先显示logo，fb_show_logo_line会返回logo占用的vertical height

然后在logo下显示extra logo, 传入的@y就是logo 的height

693 static ssize_t
694 fb_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
695 {
696     unsigned long p = *ppos;
697     struct inode *inode = file->f_path.dentry->d_inode;
698     int fbidx = iminor(inode);
699     struct fb_info *info = registered_fb[fbidx];
700     u32 *buffer, *dst;
701     u32 __iomem *src;
702     int c, i, cnt = 0, err = 0;
703     unsigned long total_size;
704
705     if (!info || ! info->screen_base)
706         return -ENODEV;
707
708     if (info->state != FBINFO_STATE_RUNNING)
709         return -EPERM;
710
711     if (info->fbops->fb_read)
712         return info->fbops->fb_read(info, buf, count, ppos);
713
714     total_size = info->screen_size;
715
716     if (total_size == 0)
717         total_size = info->fix.smem_len;
718
719     if (p >= total_size)
720         return 0;
721
722     if (count >= total_size)
723         count = total_size;
724
725     if (count + p > total_size)
726         count = total_size - p;
727
728     buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count,
729              GFP_KERNEL);
730     if (!buffer)
731         return -ENOMEM;
732
733     src = (u32 __iomem *) (info->screen_base + p);
734
735     if (info->fbops->fb_sync)
736         info->fbops->fb_sync(info);
737
738     while (count) {
739         c  = (count > PAGE_SIZE) ? PAGE_SIZE : count;
740         dst = buffer;
741         for (i = c >> 2; i--; )
742             *dst++ = fb_readl(src++);
743         if (c & 3) {
744             u8 *dst8 = (u8 *) dst;
745             u8 __iomem *src8 = (u8 __iomem *) src;
746
747             for (i = c & 3; i--;)
748                 *dst8++ = fb_readb(src8++);
749
750             src = (u32 __iomem *) src8;
751         }
752
753         if (copy_to_user(buf, buffer, c)) {
754             err = -EFAULT;
755             break;
756         }
757         *ppos += c;
758         buf += c;
759         cnt += c;
760         count -= c;
761     }
762
763     kfree(buffer);
764
765     return (err) ? err : cnt;
766 }

一般来说read
write函数都没什么可分析的，read无非就是读取设备文件的一段数据，
对于framebuffer来说，这些数据就保存在虚拟地址info->screen_base，info->screen_base是framebuffer
mem的虚拟地址，info->fix.smem_start是framebuffer
mem的物理地址，正常来说，驱动都是访问info->screen_base。

711～712 framebuffer驱动可以实现特定的read函数，也可以使用通用的实现

read的主体很简单就是通过fb_readl和fb_readb来读取info->screen_base的内容，copy到参数@buf中去

852 int
853 fb_pan_display(struct fb_info *info, struct fb_var_screeninfo *var)
854 {
855     struct fb_fix_screeninfo *fix = &info->fix;
856     unsigned int yres = info->var.yres;
857     int err = 0;
858
859     if (var->yoffset > 0) {
860         if (var->vmode & FB_VMODE_YWRAP) {
861             if (!fix->ywrapstep || (var->yoffset % fix->ywrapstep))
862                 err = -EINVAL;
863             else
864                 yres = 0;
865         } else if (!fix->ypanstep || (var->yoffset % fix->ypanstep))
866             err = -EINVAL;
867     }
868
869     if (var->xoffset > 0 && (!fix->xpanstep ||
870                  (var->xoffset % fix->xpanstep)))
871         err = -EINVAL;
872
873     if (err || !info->fbops->fb_pan_display ||
874         var->yoffset > info->var.yres_virtual - yres ||
875         var->xoffset > info->var.xres_virtual - info->var.xres)
876         return -EINVAL;
877
878     if ((err = info->fbops->fb_pan_display(var, info)))
879         return err;
880
881     info->var.xoffset = var->xoffset;
882     info->var.yoffset = var->yoffset;
883     if (var->vmode & FB_VMODE_YWRAP)
884         info->var.vmode |= FB_VMODE_YWRAP;
885     else
886         info->var.vmode &= ~FB_VMODE_YWRAP;
887     return 0;
888 }
这个函数是FBIOPAN_DISPLAY的实现，关于FBIOPAN_DISPLAY的用途, linux
kernel对这个定义也非常模糊，网上的说法也是很不确定。我的看法是这个函数用到了var参数的xoffser和yoffset，通过这两个参数可以实现屏幕内容的平滑移动。

这个调用在Android平台上还有个很重要的作用，UI刷屏就是通过FBIOPAN_DISPLAY实现的，可以实现双buffer的切换，防止tear-drop效果。

913 int
914 fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
915 {
916     int flags = info->flags;
917     int ret = 0;
918
919     if (var->activate & FB_ACTIVATE_INV_MODE) {
920         struct fb_videomode mode1, mode2;
921
922         fb_var_to_videomode(&mode1, var);
923         fb_var_to_videomode(&mode2, &info->var);
924         /* make sure we don't delete the videomode of current var */
925         ret = fb_mode_is_equal(&mode1, &mode2);
926
927         if (!ret) {
928             struct fb_event event;
929
930             event.info = info;
931             event.data = &mode1;
932             ret = fb_notifier_call_chain(FB_EVENT_MODE_DELETE, &event);
933         }
934
935         if (!ret)
936             fb_delete_videomode(&mode1, &info->modelist);
937
938
939         ret = (ret) ? -EINVAL : 0;
940         goto done;
941     }
942
943     if ((var->activate & FB_ACTIVATE_FORCE) ||
944         memcmp(&info->var, var, sizeof(struct fb_var_screeninfo))) {
945         u32 activate = var->activate;
946
947         if (!info->fbops->fb_check_var) {
948             *var = info->var;
949             goto done;
950         }
951
952         ret = info->fbops->fb_check_var(var, info);
953
954         if (ret)
955             goto done;
956
957         if ((var->activate & FB_ACTIVATE_MASK) == FB_ACTIVATE_NOW) {
958             struct fb_var_screeninfo old_var;
959             struct fb_videomode mode;
960
961             if (info->fbops->fb_get_caps) {
962                 ret = fb_check_caps(info, var, activate);
963
964                 if (ret)
965                     goto done;
966             }
967
968             old_var = info->var;
969             info->var = *var;
970
971             if (info->fbops->fb_set_par) {
972                 ret = info->fbops->fb_set_par(info);
973
974                 if (ret) {
975                     info->var = old_var;
976                     printk(KERN_WARNING "detected "
977                         "fb_set_par error, "
978                         "error code: %d\n", ret);
979                     goto done;
980                 }
981             }
982
983             fb_pan_display(info, &info->var);
984             fb_set_cmap(&info->cmap, info);
985             fb_var_to_videomode(&mode, &info->var);
986
987             if (info->modelist.prev && info->modelist.next &&
988                 !list_empty(&info->modelist))
989                 ret = fb_add_videomode(&mode, &info->modelist);
990
991             if (!ret && (flags & FBINFO_MISC_USEREVENT)) {
992                 struct fb_event event;
993                 int evnt = (activate & FB_ACTIVATE_ALL) ?
994                     FB_EVENT_MODE_CHANGE_ALL :
995                     FB_EVENT_MODE_CHANGE;
996
997                 info->flags &= ~FBINFO_MISC_USEREVENT;
998                 event.info = info;
999                 event.data = &mode;
1000                 fb_notifier_call_chain(evnt, &event);
1001             }
1002         }
1003     }
1004
1005  done:
1006     return ret;
1007 }

这个函数处理两类情况，

第一种从fb_info->modelist中删除@var对应的mode，

922~923转换var和当前fb_info->var 到viewmode

如果@var对应的viewmode不是当前正在使用的viewmode那么调用notifier函数，并从info->modelist中删除所有匹配的viewmode

第二种情况，如果有FB_ACTIVATE_FORCE标记或者新@var不等与fb_info当前的var: fb_info->var

952 一般来说驱动的fb_check_var会check @var参数，并且调整到有效值

957行，如果var->active是FB_ACTIVE_NOW， 那么激活给定的@var

968～972 设置info->var为@var, 并且调用fb_set_par设置新的framebuffer参数，改变操作模式

983 在设置新的framebuffer后需要调用fb_pan_display来更新pan display, fb_pan_display需要特定的framebuffer实现

985~989 把var对应的videomode加入到modelist中去

991～1000 广播framebuffer事件

1009 int
1010 fb_blank(struct fb_info *info, int blank)
1011 {  
1012     int ret = -EINVAL;
1013
1014     if (blank > FB_BLANK_POWERDOWN)
1015         blank = FB_BLANK_POWERDOWN;
1016
1017     if (info->fbops->fb_blank)
1018         ret = info->fbops->fb_blank(blank, info);
1019
1020     if (!ret) {
1021         struct fb_event event;
1022
1023         event.info = info;
1024         event.data = &blank;
1025         fb_notifier_call_chain(FB_EVENT_BLANK, &event);
1026     }
1027
1028     return ret;
1029 }
这个函数调用info->fbops->fb_blank， @blank指定了blank的类型，包括POWERDOWN, NORMAL HSYNC_SUSPEND, VSYNC_SUSPEND

以及重新点亮display, 对于mxc framebuffer驱动, 就是使能/无效 ipu channel

1031 static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
1032             unsigned long arg)
1033 {
1034     struct fb_ops *fb;
1035     struct fb_var_screeninfo var;
1036     struct fb_fix_screeninfo fix;
1037     struct fb_con2fbmap con2fb;
1038     struct fb_cmap cmap_from;
1039     struct fb_cmap_user cmap;
1040     struct fb_event event;
1041     void __user *argp = (void __user *)arg;
1042     long ret = 0;
1043
1044     switch (cmd) {
1045     case FBIOGET_VSCREENINFO:
1046         if (!lock_fb_info(info))
1047             return -ENODEV;
1048         var = info->var;
1049         unlock_fb_info(info);
1050
1051         ret = copy_to_user(argp, &var, sizeof(var)) ? -EFAULT : 0;
1052         break;
1053     case FBIOPUT_VSCREENINFO:
1054         if (copy_from_user(&var, argp, sizeof(var)))
1055             return -EFAULT;
1056         if (!lock_fb_info(info))
1057             return -ENODEV;
1058         acquire_console_sem();
1059         info->flags |= FBINFO_MISC_USEREVENT;
1060         ret = fb_set_var(info, &var);
1061         info->flags &= ~FBINFO_MISC_USEREVENT;
1062         release_console_sem();
1063         unlock_fb_info(info);
1064         if (!ret && copy_to_user(argp, &var, sizeof(var)))
1065             ret = -EFAULT;
1066         break;
1067     case FBIOGET_FSCREENINFO:
1068         if (!lock_fb_info(info))
1069             return -ENODEV;
1070         fix = info->fix;
1071         unlock_fb_info(info);
1072
1073         ret = copy_to_user(argp, &fix, sizeof(fix)) ? -EFAULT : 0;
1074         break;
1075     case FBIOPUTCMAP:
1076         if (copy_from_user(&cmap, argp, sizeof(cmap)))
1077             return -EFAULT;
1078         ret = fb_set_user_cmap(&cmap, info);
1079         break;
1080     case FBIOGETCMAP:
1081         if (copy_from_user(&cmap, argp, sizeof(cmap)))
1082             return -EFAULT;
1083         if (!lock_fb_info(info))
1084             return -ENODEV;
1085         cmap_from = info->cmap;
1086         unlock_fb_info(info);
1087         ret = fb_cmap_to_user(&cmap_from, &cmap);
1088         break;
1089     case FBIOPAN_DISPLAY:
1090         if (copy_from_user(&var, argp, sizeof(var)))
1091             return -EFAULT;
1092         if (!lock_fb_info(info))
1093             return -ENODEV;
1094         acquire_console_sem();
1095         ret = fb_pan_display(info, &var);
1096         release_console_sem();
1097         unlock_fb_info(info);
1098         if (ret == 0 && copy_to_user(argp, &var, sizeof(var)))
1099             return -EFAULT;
1100         break;
1101     case FBIO_CURSOR:
1102         ret = -EINVAL;
1103         break;
1104     case FBIOGET_CON2FBMAP:
1105         if (copy_from_user(&con2fb, argp, sizeof(con2fb)))
1106             return -EFAULT;
1107         if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
1108             return -EINVAL;
1109         con2fb.framebuffer = -1;
1110         event.data = &con2fb;
1111         if (!lock_fb_info(info))
1112             return -ENODEV;
1113         event.info = info;
1114         fb_notifier_call_chain(FB_EVENT_GET_CONSOLE_MAP, &event);
1115         unlock_fb_info(info);
1116         ret = copy_to_user(argp, &con2fb, sizeof(con2fb)) ? -EFAULT : 0;
1117         break;
1118     case FBIOPUT_CON2FBMAP:
1119         if (copy_from_user(&con2fb, argp, sizeof(con2fb)))
1120             return -EFAULT;
1121         if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
1122             return -EINVAL;
1123         if (con2fb.framebuffer < 0 || con2fb.framebuffer >= FB_MAX)
1124             return -EINVAL;
1125         if (!registered_fb[con2fb.framebuffer])
1126             request_module("fb%d", con2fb.framebuffer);
1127         if (!registered_fb[con2fb.framebuffer]) {
1128             ret = -EINVAL;
1129             break;
1130         }
1131         event.data = &con2fb;
1132         if (!lock_fb_info(info))
1133             return -ENODEV;
1134         event.info = info;
1135         ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event);
1136         unlock_fb_info(info);
1137         break;
1138     case FBIOBLANK:
1139         if (!lock_fb_info(info))
1140             return -ENODEV;
1141         acquire_console_sem();
1142         info->flags |= FBINFO_MISC_USEREVENT;
1143         ret = fb_blank(info, arg);
1144         info->flags &= ~FBINFO_MISC_USEREVENT;
1145         release_console_sem();
1146         unlock_fb_info(info);
1147         break;
1148     default:
1149         if (!lock_fb_info(info))
1150             return -ENODEV;
1151         fb = info->fbops;
1152         if (fb->fb_ioctl)
1153             ret = fb->fb_ioctl(info, cmd, arg);
1154         else
1155             ret = -ENOTTY;
1156         unlock_fb_info(info);
1157     }
1158     return ret;
1159 }
1160

对于这个函数没什么可说的了，介绍下每个ioctl命令的含义

FBIOGET_VSCREENINFO: Used to get the variable screen information of the frame buffer

FBIOPUT_VSCREENINFO: Used to set variable screen parameters for the frame buffer

FBIOGET_FSCREENINFO: Used to get fixiable screen parameters for the frame buffer

FBIOPUTCMAP: 设置framebuffer的color map

FBIOGETCMAP: 获取framebuffer的color map

FBIOPAN_DISPLAY：按照参数var->xoffset 和var->yoffset平移frame buffer中的内容, 可以用在双buffer的切换

FBIOGET_CON2FBMAP和FBIOPUT_CON2FBMAP实在没看明白什么意思

FBIOBLANK：使能或者点亮frame buffer, 参数arg可以是POWERDOWN, NORMAL HSYNC_SUSPEND, VSYNC_SUSPEND UNBLANK

1323 fb_mmap(struct file *file, struct vm_area_struct * vma)
1324 {
1325     int fbidx = iminor(file->f_path.dentry->d_inode);
1326     struct fb_info *info = registered_fb[fbidx];
1327     struct fb_ops *fb = info->fbops;
1328     unsigned long off;
1329     unsigned long start;
1330     u32 len;
1331
1332     if (vma->vm_pgoff > (~0UL >> PAGE_SHIFT))
1333         return -EINVAL;
1334     off = vma->vm_pgoff << PAGE_SHIFT;
1335     if (!fb)
1336         return -ENODEV;
1337     mutex_lock(&info->mm_lock);
1338     if (fb->fb_mmap) {
1339         int res;
1340         res = fb->fb_mmap(info, vma);
1341         mutex_unlock(&info->mm_lock);
1342         return res;
1343     }
1344
1345     /* frame buffer memory */
1346     start = info->fix.smem_start;
1347     len = PAGE_ALIGN((start & ~PAGE_MASK) + info->fix.smem_len);
1348     if (off >= len) {
1349         /* memory mapped io */
1350         off -= len;
1351         if (info->var.accel_flags) {
1352             mutex_unlock(&info->mm_lock);
1353             return -EINVAL;
1354         }
1355         start = info->fix.mmio_start;
1356         len = PAGE_ALIGN((start & ~PAGE_MASK) + info->fix.mmio_len);
1357     }
1358     mutex_unlock(&info->mm_lock);
1359     start &= PAGE_MASK;
1360     if ((vma->vm_end - vma->vm_start + off) > len)
1361         return -EINVAL;
1362     off += start;
1363     vma->vm_pgoff = off >> PAGE_SHIFT;
1364     /* This is an IO map - tell maydump to skip this VMA */
1365     vma->vm_flags |= VM_IO | VM_RESERVED;
1366     fb_pgprotect(file, vma, off);
1367     if (io_remap_pfn_range(vma, vma->vm_start, off >> PAGE_SHIFT,
1368                  vma->vm_end - vma->vm_start, vma->vm_page_prot))
1369         return -EAGAIN;
1370     return 0;
1371 }

man mmap可以知道mmap的作用是映射文件或设备到内存中，因此fb_mmap的作用就是把framebuffer的物理内存映射到进程的虚拟地址空间。

1334     off = vma->vm_pgoff << PAGE_SHIFT; off是这个vm area对应的文件偏移

1346 fix.smem_start是frame buffer的起始物理地址

1367~1368应该是映射为物理地址到vm area中

1546 int
1547 register_framebuffer(struct fb_info *fb_info)
1548 {
1549     int i;
1550     struct fb_event event;
1551     struct fb_videomode mode;
1552
1553     if (num_registered_fb == FB_MAX)
1554         return -ENXIO;
1555
1556     if (fb_check_foreignness(fb_info))
1557         return -ENOSYS;
1558
1559     remove_conflicting_framebuffers(fb_info->apertures, fb_info->fix.id,
1560                      fb_is_primary_device(fb_info));
1561
1562     num_registered_fb++;
1563     for (i = 0 ; i < FB_MAX; i++)
1564         if (!registered_fb[i])
1565             break;
1566     fb_info->node = i;
1567     mutex_init(&fb_info->lock);
1568     mutex_init(&fb_info->mm_lock);
1569
1570     fb_info->dev = device_create(fb_class, fb_info->device,
1571                      MKDEV(FB_MAJOR, i), NULL, "fb%d", i);
1572     if (IS_ERR(fb_info->dev)) {
1573         /* Not fatal */
1574         printk(KERN_WARNING "Unable to create device for framebuffer %d; errno = %ld\n", i, PTR_ERR(fb_info->dev));
1575         fb_info->dev = NULL;
1576     } else
1577         fb_init_device(fb_info);
1578
1579     if (fb_info->pixmap.addr == NULL) {
1580         fb_info->pixmap.addr = kmalloc(FBPIXMAPSIZE, GFP_KERNEL);
1581         if (fb_info->pixmap.addr) {
1582             fb_info->pixmap.size = FBPIXMAPSIZE;
1583             fb_info->pixmap.buf_align = 1;
1584             fb_info->pixmap.scan_align = 1;
1585             fb_info->pixmap.access_align = 32;
1586             fb_info->pixmap.flags = FB_PIXMAP_DEFAULT;
1587         }
1588     }
1589     fb_info->pixmap.offset = 0;
1590
1591     if (!fb_info->pixmap.blit_x)
1592         fb_info->pixmap.blit_x = ~(u32)0;
1593
1594     if (!fb_info->pixmap.blit_y)
1595         fb_info->pixmap.blit_y = ~(u32)0;
1596
1597     if (!fb_info->modelist.prev || !fb_info->modelist.next)
1598         INIT_LIST_HEAD(&fb_info->modelist);
1599
1600     fb_var_to_videomode(&mode, &fb_info->var);
1601     fb_add_videomode(&mode, &fb_info->modelist);
1602     registered_fb[i] = fb_info;
1603
1604     event.info = fb_info;
1605     if (!lock_fb_info(fb_info))
1606         return -ENODEV;
1607     fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
1608     unlock_fb_info(fb_info);
1609     return 0;
1610 }
这个函数为framebuffer 驱动提供了注册一个framebuffer device的接口，该函数会把@fb_info加到registered_fb中去

1570 ~1571 为frame buffer设备创建class device name

1577 fb_init_device创建frame buffer的attr文件

pixmap不知道什么意思

1600~1601 转换fb_info->var为 videomode，然后把videomode加入到modelist中

1602 把@fb_info加到registered_fb数组中

1630 int
1631 unregister_framebuffer(struct fb_info *fb_info)
1632 {
1633     struct fb_event event;
1634     int i, ret = 0;
1635
1636     i = fb_info->node;
1637     if (!registered_fb[i]) {
1638         ret = -EINVAL;
1639         goto done;
1640     }
1641
1642
1643     if (!lock_fb_info(fb_info))
1644         return -ENODEV;
1645     event.info = fb_info;
1646     ret = fb_notifier_call_chain(FB_EVENT_FB_UNBIND, &event);
1647     unlock_fb_info(fb_info);
1648
1649     if (ret) {
1650         ret = -EINVAL;
1651         goto done;
1652     }
1653
1654     if (fb_info->pixmap.addr &&
1655         (fb_info->pixmap.flags & FB_PIXMAP_DEFAULT))
1656         kfree(fb_info->pixmap.addr);
1657     fb_destroy_modelist(&fb_info->modelist);
1658     registered_fb[i]=NULL;
1659     num_registered_fb--;
1660     fb_cleanup_device(fb_info);
1661     device_destroy(fb_class, MKDEV(FB_MAJOR, i));
1662     event.info = fb_info;
1663     fb_notifier_call_chain(FB_EVENT_FB_UNREGISTERED, &event);
1664
1665     /* this may free fb info */
1666     if (fb_info->fbops->fb_destroy)
1667         fb_info->fbops->fb_destroy(fb_info);
1668 done:
1669     return ret;
1670 }
unregister_framebuffer实在没什么可看的了

1740 int fb_new_modelist(struct fb_info *info)
1741 {
1742     struct fb_event event;
1743     struct fb_var_screeninfo var = info->var;
1744     struct list_head *pos, *n;
1745     struct fb_modelist *modelist;
1746     struct fb_videomode *m, mode;
1747     int err = 1;
1748
1749     list_for_each_safe(pos, n, &info->modelist) {
1750         modelist = list_entry(pos, struct fb_modelist, list);
1751         m = &modelist->mode;
1752         fb_videomode_to_var(&var, m);
1753         var.activate = FB_ACTIVATE_TEST;
1754         err = fb_set_var(info, &var);
1755         fb_var_to_videomode(&mode, &var);
1756         if (err || !fb_mode_is_equal(m, &mode)) {
1757             list_del(pos);
1758             kfree(pos);
1759         }
1760     }
1761
1762     err = 1;
1763
1764     if (!list_empty(&info->modelist)) {
1765         if (!lock_fb_info(info))
1766             return -ENODEV;
1767         event.info = info;
1768         err = fb_notifier_call_chain(FB_EVENT_NEW_MODELIST, &event);
1769         unlock_fb_info(info);
1770     }
1771
1772     return err;
1773 }
测试info->modelist中的每一个mode，从这个modelist中删除无效的mode节点

1787 int fb_get_options(char *name, char **option)
1788 {
1789     char *opt, *options = NULL;
1790     int opt_len, retval = 0;
1791     int name_len = strlen(name), i;
1792
1793     if (name_len && ofonly && strncmp(name, "offb", 4))
1794         retval = 1;
1795
1796     if (name_len && !retval) {
1797         for (i = 0; i < FB_MAX; i++) {
1798             if (video_options[i] == NULL)
1799                 continue;
1800             opt_len = strlen(video_options[i]);
1801             if (!opt_len)
1802                 continue;
1803             opt = video_options[i];
1804             if (!strncmp(name, opt, name_len) &&
1805                 opt[name_len] == ':')
1806                 options = opt + name_len + 1;
1807         }
1808     }
1809     if (options && !strncmp(options, "off", 3))
1810         retval = 1;
1811
1812     if (option)
1813         *option = options;
1814
1815     return retval;
1816 }

从kernel cmd 参数中提取framebuffer相关的选项