Hi Russell, On Mon, Mar 04, 2019 at 04:10:47PM +0000, Russell King - ARM Linux admin wrote: > On Mon, Mar 04, 2019 at 11:47:00AM +0100, Antoine Tenart wrote: > > > > I agree having a per-driver behaviour is not something we want. As I > > understand it, there is no behaviour enforced currently regarding this > > matter. I agree both cases have their pros and cons: > > - It's weird to have an interface reporting being UP when it's not > > really. > > What about when an interface is listening for wake-on-lan packets? > > Let's say board 1 is powered down and has WoL enabled. Board 2 is > as per your configuration. Board 2's interface reports that the > link is up. Most of the packets that would be sent out the > interface end up disappearing into a black hole in the same way > as your original scenario.
I see your point, in the WoL case the link would be reported as being up as the PHY on board 1 would be functional (at least to process WoL packets) so the link between the two PHYs would be established and reporting a link being UP, but not entirely functional. That's kind of a fair point, but not exactly the same. In such case some packets might have an effect, whereas in the case I described earlier not a single packet would make sense. But also I might not be aware of other valid cases. > The only case where what you're suggesting makes sense is a point-to- > point link between two systems, which is not the norm. > > More than that, when board 1 boots, initially the link will be up > from reset. When the kernel eventually boots with your patch, the > link will then go down until board 1 configures the interface. So, > board 2 sees that the interface comes up, and could assume that > board 1 is alive and well - but it isn't because (eg) it's in the > boot loader. This depends on the bootloader, but OK, that is what's happening in this very case. I'm not fully convinced this relates to the scenario I described. The link would be up and you're right could be not functional because the way the bootloader works. And this is temporary. > Basically, what I'm pointing out is that even in your minority > scenario, reasoning that board 2 should not see "link up" status > until board 1's interface is configured is not reasonable. > > The link status is about the physical connectivity on the local > interface, it is not about the link between the interfaces on the > two machines. Right. The thing I find odd here is there is no physical connectivity between the MACs (one is in reset), only between one MAC and the LP's PHY. Given your definition of a link being up "between the interfaces", OK, that makes sense if we talk about the PHYs. It also means we do not have the same behaviour at boot time between an interface using a PHY, and one directly connected to serdes lanes. So, I don't have a strong opinion about this, and it's not a big issue either way. I think the discussion moved into what should be the default state of a PHY a probe time, as it seems there are no policy being enforced right now. Thanks, Antoine -- Antoine Ténart, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
