Where does Xorg fallback to ?

[小飞珑]

Hi, 
   I am looking into Xorg for performance optimization, and want to do some software acceleration for the Xorg fallback functions when the hardware acceleration is not available. I am now using a notebook with intel display card. In the UXA driver, I force the driver to use fallback funcs instead of the Accelerated funcs. As in uxa/uxa-accel.c -> uxa_copy_area(), I made uxa_screen->force_fallback = 1, force uxa driver to call uxa_check_copy_area()->fbCopyArea(), but the fbCopyArea seemed NOT to be the fbCopyArea in Xorg fb/fbcopy.c ! For I added return NULL immediately  in the beginning of fb/fbcopy.c -> fbCopyArea(), but made no difference, but if I comment the fbCopyArea() in uxa/uxa-unaccel.c the display is ruined. It seemed that the above two fbCopyArea() functions are not the same. Where did the Xorg fallback to? NOT to the fb/fbcopy.c ? I am eager to know that, could some body tell ? Thanks a lot!
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