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Linux X.Org driver
This chip is supported by the 'siliconmotion' driver as part of the X.Org distribution
Display on the internal LCD works as long as you set the monitor settings correct.
External VGA port
Linux kernel Framebuffer driver
There are two framebuffer drivers. One is sm712.c. The other is lynxfb.c. The sm712.c driver comes with the Embedded Linux Development Kit (eldk) as part of the stock Linux kernel and seems to work well (but possibly needs hardware-dependant tweaks in some embedded environments.) The second one, lynxfb.c was obtained directly from Silicon Motion and won't work without tweaks in some environments.
There is also limited framebuffer support for this chip in embedded devices as part of the "U-Boot" boot loader. This works well and is based on the second (lynxfb) driver.