Yes, they all have same product number.
They are one IP.
O.K, this is the sort of information which is useful to have in the
commit message. Basically anything which is odd about your PHY it is
good to mention, because reviewers are probably going to notice and
ask.
The difference is feature set it's enabled by fusing in silicon.
For example, GPY115 has 10/100/1000Mbps support, so in the ability
register 2.5G capable is 0.
GPY211 has 10/100/1000/2500Mbps support, so in the capability register
2.5G capable is 1.
I assume it is more than just the capability register? Linux could
easily ignore that and make use of 2.5G if it still actually works.
Andrew