Tegra was used in android tablets, I had a couple. Not sure what the licence status was, but it was supported in cyanogen, so they must have had to make some changes to the kernel for that?
Certainly some of the stuff the upstreamed was to support their drivers, but they would have also been working on other more general things to support their super computers and other HPC stuff.
They also had a chipset for intel motherboards (which I can’t find anything about), which may have had some work required?
I don’t really know exactly the scope of all the work, but they have been in the top 20 companies for kernel development for a long time, and I assuming it can’t just be supporting their own drivers.
Its hard to find the stats, but from here: https://bootlin.com/community/contributions/kernel-contributions/ you can click through and get breakdowns per kernel release: https://web.archive.org/web/20160803012713/remword.com/kps_result/3.8_whole.html
I kinda like the keyboard shortcuts for i3/sway, but wish there was some level of mouse integration/polish like gnome. Will try forge, thanks!