On Fri, Sep 06, 2024 at 09:22:29AM -0700, Florian Fainelli wrote: > On 9/6/24 09:11, Andrew Lunn wrote: > > > > 10Base-T1 often does not have autoneg, so preferred-master & > > > > preferred-slave make non sense in this context, but i wounder if > > > > somebody will want these later. An Ethernet switch is generally > > > > preferred-master for example, but the client is preferred-slave. > > > > > > > > Maybe make the property a string with supported values 'forced-master' > > > > and 'forced-slave', leaving it open for the other two to be added > > > > later. > > > > > > My two cents, don't take it as a nack or any strong disagreement, my > > > experience with SPE is still limited. I agree that for SPE, it's > > > required that PHYs get their role assigned as early as possible, > > > otherwise the link can't establish. I don't see any other place but DT > > > to put that info, as this would be required for say, booting over the > > > network. This to me falls under 'HW representation', as we could do the > > > same with straps. > > > > > > However for preferred-master / preferred-slave, wouldn't we be crossing > > > the blurry line of "HW description => system configuration in the DT" ? > > > > Yes, we are somewhere near the blurry line. This is why i gave the > > example of an Ethernet switch, vs a client. Again, it could be done > > with straps, so following your argument, it could be considered HW > > representation. But if it is set wrong, it probably does not matter, > > auto-neg should still work. Except for a very small number of PHYs > > whos random numbers are not random... > > Having had to deal with an Ethernet PHY that requires operating in slave > mode "preferably" in order to have a correct RXC duty cycle, if you force > both sides of the link to "slave", auto-negotiation will fail, however > thanks to auto-negotiation you can tell that there was a master/slave > resolution failure. (This reminds me I need to send the patch for that PHY > errata at some point). > > In the case that Oleksij seems to be after, there is no auto-negotiation (is > that correct?), so it seems to me that the Device Tree is coming to the > rescue of an improperly strapped HW, and is used as a way to change the > default HW configuration so as to have a fighting chance of having a > functional link. That is not unprecedented, but it is definitively a bit > blurry... Yes, there is no auto-negotiation on T1 PHY variants, so the DT property is to fix broken or not existing for some reason HW straps. -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
