Messages in this thread | | | Date | Thu, 21 Jul 2022 22:06:32 +0100 | From | "Russell King (Oracle)" <> | Subject | Re: [PATCH v2 08/11] net: phylink: Adjust advertisement based on rate adaptation |
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On Thu, Jul 21, 2022 at 08:36:03PM +0200, Andrew Lunn wrote: > > 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.
-- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
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