AM4378: AM4378 DDR3 trace routing

FYI, I asked one of my colleagues who is deeper on the hardware side to review my comments and to make any further suggestions.

Actually, the Manhattan distance is just the x/y distance from point to point (not following the trace around). So you may be in violation of parameter 15 in table 5-58, plus you are close to the max trace lengths. Other factors which may affect robustness:
-number of vias: Based on your drawing, it looks like you routed these signals on one layer, which is good. Any via mismatches will degrade the signal
-Your drawing shows 90deg angles on the signals, which would not be good. I'm assuming this is just a simplified drawing and you have more gradual turns in those signals
-stackup will also be important (Table 5-52). Hopefully you have a full ground reference under the DDR routing region

As Brad said, I think ideally the placement and orientation of the memories relative to the processor could have been more optimized, and would have resulted in shorter traces and better routing.

With your prototypes, some things that you can do to give you more confidence is to increase DDR frequency beyond 400MHz. Although this is out of spec, it can give you some idea of how much margin you have (ensure you adjust DDR configuration accordingly). Also, memory stress tests can be performed (Linux memtester is a good one, or set up some DMAs).

Regards,
James