sun4i_frontend driver not work as expect on A31s

[highlab highlab]

Hello,

   I found that when graphic data processed by sun4i_frontend,  the frontend seems output black screen on allwinner A31S board, do you know what is going wrong. 

   I have test the sun4i_frontend driver on a10/a20 board, it work perfect.

   When  graphic  data not going throught frontend and just processed by backend,  graphic  data output to HDMI is perfect too.