VFF_WPT
mtk_uart_apdma_write(c, VFF_WPT, 0);
wpt = mtk_uart_apdma_read(c, VFF_WPT);
mtk_uart_apdma_write(c, VFF_WPT, wpt);
wg = mtk_uart_apdma_read(c, VFF_WPT);