Checked the schematics
- DSI and CSI are 100ohm differential pairs.
TBH this is all down to best design principles. Where designing products that need to pass QA tests, you do everything right. It also reduces issues when doing EMC testing. If you're doing a one off, then suck it and see. Abide by the principles where you can, but don't obsess over them.
You asked the question over why there were multiple grounds, but feel free to try it out with fewer.
for one of my lash ups that works quite happily, however it is only running at 432Mbit/s, or 216MHz link frequency. The SMA cables were cut as accurately as possible to make them the same length but are going to be a number of mm different, and the dodgy soldering onto the camera board isn't going to be perfectly impedance matched. It works, but I wouldn't look at selling a product built like that.
I vaguely recall a very old story over the design of two CPUs by different manufacturers. One radiated like anything and ran hot, whilst the other ran significantly cooler and didn't radiate anywhere near as much. The difference was that one had used sharp 90deg bends in the tracking, whilst the other had nicely rounded corners. (I want to say this was the early Intel x86's vs Motorola 6800, but that could be totally bogus).
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.