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;
}
}
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
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？
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
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
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
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
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
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
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
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
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
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。
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
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
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
