With respect to the changelog for commit 52df445f29b7 ("i2c: rcar: revoke START request early"), in particular: "This patch improves the situation but sadly does not completely fix it. It is still to be researched if we can do better given this HW design." This is still the best we can do so far, isn't it?
Yes, I think so. Gen3 seems to have this fixed in HW.