Re: [PATCH iwl-next v4 0/3] igc: add support for forcing link speed without autonegotiation

[Andrew Lunn]

> I agree that for normal Ethernet use, auto-negotiation on both link
> partners is safer and avoids the issues you mentioned.
> 
> The reason for this patch is the more specific PROFINET Fast Start Up
> (FSU) use case. For FSU, the requirement is different from normal Ethernet
> use. It is intended for deterministic startup, for example in industrial
> robot/tool-change applications.
> 
> One of the startup optimizations is to use "fixed transmission parameters"
> instead of automatic detection in the profinet specification:
>   https://us.profinet.com/profinet_tech/fast-start-up/

Automotive also have similar requirements. For them, Autoneg is slow,
takes around 1 second, where as a fixed link is operative very
fast. There are even some automotive ethernet devices which don't even
support autoneg.

So this use case makes sense to me, for embedded systems. If the
hardware can do it, any most PHYs can, i see no reason not to support
it. And anything using phylib gets it for free.

	Andrew