On Thu, Jul 21, 2022 at 08:36:03PM +0200, Andrew Lunn wrote:

quoted

I guess it would depend on the structure of the PHY - whether the PHY
is structured similar to a two port switch internally, having a MAC
facing the host and another MAC facing the media side. (I believe this
is exactly how the MACSEC versions of the 88x3310 are structured.)

If you don't have that kind of structure, then I would guess that doing
duplex adaption could be problematical.

If you don't have that sort of structure, i think rate adaptation
would have problems in general. Pause is not very fine grained. You
need to somehow buffer packets because what comes from the MAC is
likely to be bursty. And when that buffer overflows, you want to be
selective about what you throw away. You want ARP, OSPF and other
signalling packets to have priority, and user data gets
tossed. Otherwise your network collapses.

I don't think rate adaption is that inteligent - it's all about slowing
the MAC down to the speed of the media. From what I remember looking at
pause frames, they can specify how long to delay further transmission
by the receiver, and I would expect this to be set according to the
media speed for setups that use pause packets.

For those which don't, then that's a whole different ball game, because
they tend not to have MACs, and then you're probably down to the
capabilities of nothing more than a FIFO in the PHY.

-- 
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