整个BBB的调试手段搞明白了，下面的工作是针对编译过程中出现的问题，逐一解决，以此提高对内核的认识。
首先是config。自从按照的步骤实施之后，
问题就来了，首先是config发现了错误，现象：
drivers/video/Kconfig:60:error: recursive dependency detected!
drivers/video/Kconfig:60: symbol FB is selected by DRM_KMS_HELPER
drivers/gpu/drm/Kconfig:28: symbol DRM_KMS_HELPER is selected by DRM_TILCDC
drivers/gpu/drm/tilcdc/Kconfig:1: symbol DRM_TILCDC depends on BACKLIGHT_LCD_SUPPORT
drivers/video/backlight/Kconfig:5: symbol BACKLIGHT_LCD_SUPPORT is selected by FB_BACKLIGHT
drivers/video/Kconfig:247: symbol FB_BACKLIGHT is selected by PMAC_BACKLIGHT
drivers/macintosh/Kconfig:134: symbol PMAC_BACKLIGHT depends on FB
怎么办，首先学习makefile中的select和depends on 的区别，网上资料很多，不多说了。
逐个分析这几个Kconfig文件，涉及的东西太多，一时间也没有头绪，怎么办，心想这么明显的问题，高版本肯定是解决了，
于是和高版本对比，发现：
文件drivers/gpu/drm/tilcdc/Kconfig：
config DRM_TILCDC
tristate "DRM Support for TI LCDC Display Controller"
depends on DRM && OF && BACKLIGHT_LCD_SUPPORT
select DRM_KMS_HELPER
select DRM_KMS_CMA_HELPER
select DRM_GEM_CMA_HELPER
select OF_VIDEOMODE
select OF_DISPLAY_TIMING
select BACKLIGHT_CLASS_DEVICE
help
Choose this option if you have an TI SoC with LCDC display
controller, for example AM33xx in beagle-bone, DA8xx, or
OMAP-L1xx. This driver replaces the FB_DA8XX fbdev driver.
高版本的内核代码已经修改为
config DRM_TILCDC
tristate "DRM Support for TI LCDC Display Controller"
depends on DRM && OF && ARM
......
select BACKLIGHT_LCD_SUPPORT
help
Choose this option if you have an TI SoC with LCDC display
controller, for example AM33xx in beagle-bone, DA8xx, or
OMAP-L1xx. This driver replaces the FB_DA8XX fbdev driver.
ok，知道了，修改代码，问题解决。
