1. drm_mode_addfb2

2. drm_internal_framebuffer_create

3. drm_fb_cma_create->drm_gem_fb_create->drm_gem_fb_create_with_funcs

4. drm_gem_fb_alloc

4.1 drm_helper_mode_fill_fb_struct

4.2 drm_framebuffer_init

5. 调用流程图

书接上回，使用drmIoctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create)接口创建了一块内存放在了gem cma的对象里。

gem obj创建之后需要与一块drm_framebuffer进行绑定使用，因为最终刷图使用的是fb。使用下面接口会创建drm_framebuffer并与上节创建的gem obj进行绑定。

目前使用较多的就是drm_mode_addfb2接口，该接口完成了下面的功能。

1. drm_mode_addfb2

int drm_mode_addfb2(struct drm_device *dev,void *data, struct drm_file *file_priv)
{struct drm_mode_fb_cmd2 *r = data;struct drm_framebuffer *fb;if (!drm_core_check_feature(dev, DRIVER_MODESET))return -EINVAL;fb = drm_internal_framebuffer_create(dev, r, file_priv);if (IS_ERR(fb))return PTR_ERR(fb);DRM_DEBUG_KMS("[FB:%d]\n", fb->base.id);r->fb_id = fb->base.id;/* Transfer ownership to the filp for reaping on close */mutex_lock(&file_priv->fbs_lock);list_add(&fb->filp_head, &file_priv->fbs);mutex_unlock(&file_priv->fbs_lock);return 0;
}

drm_mode_addfb2主要做了三件大事：

（1）调用drm_internal_framebuffer_create创建一个drm_framebuffer。

（2）把drm_framebuffer的struct drm_mode_object的ID返回给应用。

（3）加到file_priv的fbs链表中。

下面我们看一下函数drm_internal_framebuffer_create。

2. drm_internal_framebuffer_create

struct drm_framebuffer *
drm_internal_framebuffer_create(struct drm_device *dev,const struct drm_mode_fb_cmd2 *r,struct drm_file *file_priv)
{........fb = dev->mode_config.funcs->fb_create(dev, file_priv, r);if (IS_ERR(fb)) {DRM_DEBUG_KMS("could not create framebuffer\n");return fb;}return fb;
}

检查参数，然后调用dev->mode_config.funcs->fb_create(dev, file_priv, r)，可以自己实现，也可以使用内核现成的drm_fb_cma_create。

3. drm_fb_cma_create->drm_gem_fb_create->drm_gem_fb_create_with_funcs


struct drm_framebuffer *
drm_gem_fb_create_with_funcs(struct drm_device *dev, struct drm_file *file,const struct drm_mode_fb_cmd2 *mode_cmd,const struct drm_framebuffer_funcs *funcs)
{const struct drm_format_info *info;struct drm_gem_object *objs[4];struct drm_framebuffer *fb;int ret, i;info = drm_get_format_info(dev, mode_cmd);if (!info)return ERR_PTR(-EINVAL);for (i = 0; i < info->num_planes; i++) {unsigned int width = mode_cmd->width / (i ? info->hsub : 1);unsigned int height = mode_cmd->height / (i ? info->vsub : 1);unsigned int min_size;objs[i] = drm_gem_object_lookup(file, mode_cmd->handles[i]);if (!objs[i]) {DRM_DEV_ERROR(dev->dev, "Failed to lookup GEM\n");ret = -ENOENT;goto err_gem_object_put;}min_size = (height - 1) * mode_cmd->pitches[i]+ width * info->cpp[i]+ mode_cmd->offsets[i];if (objs[i]->size < min_size) {// DRM_DEV_ERROR(dev->dev, "objs %d Size(%d %d) error\n",// 	i, objs[i]->size, min_size);drm_gem_object_put_unlocked(objs[i]);ret = -EINVAL;goto err_gem_object_put;}}fb = drm_gem_fb_alloc(dev, mode_cmd, objs, i, funcs);if (IS_ERR(fb)) {ret = PTR_ERR(fb);DRM_DEV_ERROR(dev->dev, "alloc error %d\n", ret);goto err_gem_object_put;}return fb;err_gem_object_put:for (i--; i >= 0; i--)drm_gem_object_put_unlocked(objs[i]);return ERR_PTR(ret);
}

（1）通过应用提供的handle，使用drm_gem_object_lookup找到上次创建的gem obj。

（2）调用drm_gem_fb_alloc，分配一个drm_framebuffer，将gem obj赋值给framebuffer中的obj。

4. drm_gem_fb_alloc

static struct drm_framebuffer *
drm_gem_fb_alloc(struct drm_device *dev,const struct drm_mode_fb_cmd2 *mode_cmd,struct drm_gem_object **obj, unsigned int num_planes,const struct drm_framebuffer_funcs *funcs)
{struct drm_framebuffer *fb;int ret, i;fb = kzalloc(sizeof(*fb), GFP_KERNEL);if (!fb)return ERR_PTR(-ENOMEM);drm_helper_mode_fill_fb_struct(dev, fb, mode_cmd);for (i = 0; i < num_planes; i++)fb->obj[i] = obj[i];ret = drm_framebuffer_init(dev, fb, funcs);if (ret) {DRM_DEV_ERROR(dev->dev, "Failed to init framebuffer: %d\n",ret);kfree(fb);return ERR_PTR(ret);}return fb;
}

4.1 drm_helper_mode_fill_fb_struct

void drm_helper_mode_fill_fb_struct(struct drm_device *dev,struct drm_framebuffer *fb,const struct drm_mode_fb_cmd2 *mode_cmd)
{int i;fb->dev = dev;fb->format = drm_get_format_info(dev, mode_cmd);fb->width = mode_cmd->width;fb->height = mode_cmd->height;for (i = 0; i < 4; i++) {fb->pitches[i] = mode_cmd->pitches[i];fb->offsets[i] = mode_cmd->offsets[i];}fb->modifier = mode_cmd->modifier[0];fb->flags = mode_cmd->flags;
}

将应用传入的长，宽，format，pitch，flag等填充framebuffer结构体。

4.2 drm_framebuffer_init

int drm_framebuffer_init(struct drm_device *dev, struct drm_framebuffer *fb,const struct drm_framebuffer_funcs *funcs)
{int ret;if (WARN_ON_ONCE(fb->dev != dev || !fb->format))return -EINVAL;INIT_LIST_HEAD(&fb->filp_head);fb->funcs = funcs;ret = __drm_mode_object_add(dev, &fb->base, DRM_MODE_OBJECT_FB,false, drm_framebuffer_free);if (ret)goto out;mutex_lock(&dev->mode_config.fb_lock);dev->mode_config.num_fb++;list_add(&fb->head, &dev->mode_config.fb_list);mutex_unlock(&dev->mode_config.fb_lock);drm_mode_object_register(dev, &fb->base);
out:return ret;
}

相关字段填充完成后会将fb添加进dev->mode_config.fb_list便于后面使用的时候通过id进行查找, drm的组件都是通过dev->mode_config中的链表进行管理的，只要拿到mode_config就可以拿到drm相关信息。

至此drm_framebuffer已经创建完毕。通过r->fb_id = fb->base.id;将fb_id返回给用户。