Wow, that's incredible. Is your code open-source? I'd love to take a look at it in order to see what you're doing; Intel's documentation is a little overwhelming for someone without extensive experience of embedded systems like me. Given that it's the Intel G45, is this driver also compatible with most Intel HD integrated graphics chips?
Yes, my code is available here on github
(beware of C++ operator overloading). I did not push the DDC code for getting EDID information without the BIOS yet (which is required to discover the video modes that a connected monitor supports). I also did not spend much time on cleaning up the code yet. I plan to write a wiki page that explains how to do the mode set.
About portability to other graphics chips: The driver as-is should work for all (non-mobile) third generation Intel graphics chips from this list
(i.e. all card produced in 2006-2009). There would be minor changes required for generation 3 chips. I don't think it is worthwhile to support anything below generation 3.
For later generations: Regarding the display registers there are two notable overhauls in Intel HD graphics chips: The first is the introduction of Ironlake and the second the introduction of Haswell. All chips in between do not need many changes in the driver. The greatest difference between Ironlake and G45 is that Ironlake shares clock sources between different display pipelines so you need a mechanism to allocate clock sources (which is trivial if you only use one display pipe). I did not yet look into the changes introduced with Haswell.
That being said I do think that it is possible to support those generations if you want to. I do not think that writing a mode setting driver for the newer generations is much more complicated than writing a mode setting driver for the G45. The hardware might be a bit more complex but it is also much better documented. I did not choose G45 because it is easy; I just chose it because that is the hardware that I had available