I have tested with full screen invalidate. It doesn't look pretty when moving a window.. but mouse pointer is ok. I have tried the below. Result: No traces if moving up , left or right. Down , traces. So the start address is wrong, probably.
cache_clean_invalidate_data(xxx+invalid,(size.count()*sizeof(Pixel))-invalid);
The imx8 doesn't use cached dma-buffer? Is there soeḿething (apart from imx53) that does use cached framebuffer?
/Michael