For more information read the Debian bug report, with attached patch:
it seems to be present a similar problem on PowerPC too.
board: Acube Sam460ex with SM502
I sent out a series of patches to the xorg-devel list. Feel free to revive
Note that the title of this bug isn't exactly true, because Xorg works just fine without patching on a Loongson-based Fuloong system which uses a SiS 315 video chip.
The problem seems to be related specifically to a Silicon Motion video chip in combination with some non-x86 architectures.
opened a new bug ticket for PowerPC
Mass closure: This bug has been untouched for more than six years, and is not obviously still valid. Please file a new report if you continue to experience issues with a current server.