Hi, Okay, I think it's time to get to the bottom of this, and below are my ramblings so far. According to IEEE 802.3 80.1.3, XLGMII is the 40 Gb/s MII and CGMII is the 100 Gb/s MII. 81.1 goes on to state: The XLGMII/CGMII has the following characteristics: a) The XLGMII supports a speed of 40 Gb/s. b) The CGMII supports a speed of 100 Gb/s. c) Data and delimiters are synchronous to a clock reference. d) It provides independent 64-bit wide transmit and receive data paths. e) It supports full duplex operation only. That seems very clear. According to https://www.synopsys.com/dw/ipdir.php?ds=dwc_ether_enterprise_mac XLGMII operates at 25 Gb/s, 40 Gb/s, 50 Gb/s and 100 Gb/s. This appears to "disagree" with IEEE 802.3. It appears, at least to me, that CGMII and XLGMII are physically similar interfaces, the only difference seems to be the speed of operation, so it would be entirely possible to have a MAC that can operate at both speeds - or indeed at other speeds such as Synopsys' "XLGMII" MAC. Now, the problem is... phylink interprets PHY_INTERFACE_MODE_XLGMII to mean the IEEE 802.3 defined 40 Gb/s mode - in that it _only_ supports 40 Gb/s over that interface mode. Clearly, that's the right thing to be doing, because this is what IEEE defines and vendor stuff doesn't apply for generic code. phylib hasn't defined PHY_INTERFACE_MODE_CGMII yet, so phylink doesn't provide that (maybe it should.) However, when it does, phylink will then allow 100 Gb/s over CGMII. Are there other standards that define 25 and 50 Gb/s over an XLGMII- like link? Given the way things are at present, it means that the switch statement in stmmac_mac_link_up() for PHY_INTERFACE_MODE_XLGMII, only one case will ever be used - SPEED_40000. I'm guessing this isn't a problem as no one has reported any problems. Then... there's the inclusion of 10G, 2.5G and 1G in the XLGMII switch. The above link to Synopsys website suggests that XGMII is used for 10G and GMII for 1G. Given that this is just the MAC, and we would normally have a PCS after it (which may be XPCS), the interface used between the MAC and PCS isn't all that relevant, since PHY_INTERFACE_MODE_xxx primerily defines the interface to any PHY that is connected, and as a secondary function the interface to fiber (since [MAC - PCS - Serdes] - PHY - media and [MAC - PCS - Serdes] - media are common, it has made sense to use the PHY interface mode to define the protocol used on that part of the link that a PHY _could_ be connected to.) So, I'm not convinced that the fact that this MAC core uses XLGMII, XGMII and GMII has any relevance to the PHY_INTERFACE_MODE_ passed by phylink into functions such as stmmac_mac_link_up(), _unless_ a PHY is connected directly to the MAC. If XPCS is connected, that interface mode would be whatever XPCS is using to talk to the "outside world" not what the connection is between the MAC and XPCS. If we want to know what that is, then stmmac needs to be asking XPCS for that information (and maybe phylink needs to get that from its PCS on behalf of the MAC driver.) I think there's a lot that needs to be thought about here. Part 2 of this will be USXGMII... which I'll do as a separate email. Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
