Merging Allwinner support [LWN.net]

Merging Allwinner support

Posted Sep 16, 2014 15:41 UTC (Tue) by mpr22 (subscriber, #60784)
In reply to: Merging Allwinner support by lkcl
Parent article: Merging Allwinner support

Footnote: gigabit Ethernet's actually a bad example, because I have encountered (and dealt with the software implications of) combinations of gigabit PHY and gigabit switch that would misnegotiate if the connection between them only provided the two pairs needed for 100Mbit. Specifically, they'd successfully autonegotiate a gigabit connection, then fail to actually send useful network packets because you can't do gigabit without all four pairs.

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Merging Allwinner support

Posted Sep 17, 2014 7:32 UTC (Wed) by lkcl (guest, #60496) [Link] (1 responses)

interesting... that sounds bad, and i am curious as to how that actually occurs, and to know what the circumstances are where GbE would be negotiated when the PHY (on a CPU Card) is only 10/100 capable and cannot (and will not) *ever* advertise that it has GbE capabilitiy. it sounds like either a firmware fault with the switch or a hardware (design) fault of some kind.

Merging Allwinner support

Posted Sep 22, 2014 16:43 UTC (Mon) by james (guest, #1325) [Link]

This sounds to me like an issue with the cable, not the NIC or switch.

In particular, there exist Cat 5 splitters which enable you to run two 10/100 connections over a single Cat 5 cable run (one example from a quick Google search). They're purely electrical, and you need two, one at each end. Each has two sockets: one is a pass-through for the two pairs a normal 10/100 Ethernet connection uses, and the other uses the other two pairs of a Cat 5 connection.

These are less than elegant, but in certain circumstances (no budget or time to do it properly, and particularly historically) they're not such a bad solution provided everyone involved is aware of their limitations.

I haven't come across anyone doing this actually in the cabling itself for networking, although I'm very sure people have tried it. I've seen people doing a similar one-pair-of-Cat-5-per-socket for digital telephony with Cat 5 wiring, and that's bad enough...