fbmem.c讲解

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 }

实现了logo的几种软件旋转
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

fb_rotate_logo_ud旋转180度

fb_rotate_logo_cw 顺时针转动90度

fb_rotate_logo_ccw 逆时针转动90度

 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

FB_ROTATE_UD upper down 颠倒旋转（180度旋转）

FB_ROTATE_CW clockwise旋转(顺时针)

FB_ROTATE_CCW counter clockwise旋转(逆时针旋转)

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 = ␣
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