On Tue, Apr 16, 2024 at 07:12:49PM +0100, Russell King (Oracle) wrote: > On Tue, Apr 16, 2024 at 07:23:03PM +0200, Stefan Eichenberger wrote: > > Hi Russell and Andrew, > > > > On Tue, Apr 16, 2024 at 05:24:02PM +0100, Russell King (Oracle) wrote: > > > On Tue, Apr 16, 2024 at 06:02:08PM +0200, Andrew Lunn wrote: > > > > On Tue, Apr 16, 2024 at 05:43:16PM +0200, Stefan Eichenberger wrote: > > > > > Hi Andrew, > > > > > > > > > > Thanks a lot for the feedback. > > > > > > > > > > On Tue, Apr 16, 2024 at 03:46:19PM +0200, Andrew Lunn wrote: > > > > > > On Tue, Apr 16, 2024 at 02:10:32PM +0200, Stefan Eichenberger wrote: > > > > > > > Add a new device tree property to disable SGMII autonegotiation and > > > > > > > instead use the option to match the SGMII speed to what was negotiated > > > > > > > on the twisted pair interface (tpi). > > > > > > > > > > > > Could you explain this is more detail. > > > > > > > > > > > > SGMII always runs its clocks at 1000Mbps. The MAC needs to duplicate > > > > > > the symbols 100 times when running at 10Mbs, and 10 times when running > > > > > > at 100Mbps. > > > > > > > > > > Currently, the mxl-gpy driver uses SGMII autonegotiation for 10 Mbps, > > > > > 100 Mbps, and 1000 Mbps. For our Ethernet controller, which is on an > > > > > Octeon TX2 SoC, this means that we have to enable "in-band-status" on > > > > > the controller. This will work for all three speed settings. However, if > > > > > we have a link partner that can do 2.5 Gbps, the mxl-gpy driver will > > > > > disable SGMII autonegotiation in gpy_update_interface. This is not > > > > > supported by this Ethernet controller because in-band-status is still > > > > > enabled. Therefore, we will not be able to transfer data at 2.5 Gbps, > > > > > the SGMII link will not go into a working state. > > > > > > > > This is where i expect Russel to point out that SGMII does not support > > > > 2.5G. What you actually mean is that the PHY swaps to 2500BaseX. And > > > > 2500BaseX does not perform speed negotiation, since it only supports > > > > 2500. So you also need the MAC to swap to 2500BaseX. > > > > > > Yes, absolutely true that SGMII does not support 2.5G... and when > > > operating faster, than 2500base-X is normally used. > > > > > > How, 2500base-X was slow to be standardised, and consequently different > > > manufacturers came up with different ideas. The common theme is that > > > it's 1000base-X up-clocked by 2.5x. Where the ideas differ is whether > > > in-band negotiation is supported or not. This has been a pain point for > > > a while now. > > > > > > As I mentioned in my previous two messages, I have an experimental > > > patch series that helps to address this. > > > > > > The issue is that implementations mix manufacturers, so we need to > > > know the capabilities of the PHY and the capabilities of the PCS, and > > > then hope that we can find some common ground between their > > > requirements. > > > > > > There is then the issue that if you're not using phylink, then... > > > guess what... you either need to convert to use phylink or implement > > > the logic in your own MAC driver to detect what the PHY is doing > > > and what its capabilities are - but I think from what you've said, > > > you are using phylink. > > > > Thanks for the patch series and the explanation. In our use case we have > > the mismatch between the PHY and the mvpp2 driver in 2500BaseX mode. > > Ah, mvpp2. This is one of those cases where I think you have a > disagreement between manufacturers over 2500base-X. > > Marvell's documentation clearly states that when operating in 1000base-X > mode, AN _must_ be enabled. Since programming 2500base-X is programming > the mvpp2 hardware for 1000base-X and then configuring the COMPHY to > clock faster, AN must also be enabled when operating at 2500base-X. > > It seems you've coupled it with the mxl-gpy PHY which doesn't apparently > support AN when in 2500base-X. > > Welcome to the mess of 2500base-X, and sadly we finally have the > situation that I've feared for years: one end of a 2500base-X link > that's documented as requiring AN, and the other end not providing it. > > Sigh. If only the IEEE 802.3 committee had been more pro-active and > standardised 2500base-X _before_ manufacturers went off and did their > own different things. I also checked the datasheet and you are right about the 1000base-X mode and in-band AN. What worked for us so far was to use SGMII mode even for 2.5Gbps and disable in-band AN (which is possible for SGMII). I think this works because as you wrote, the genphy just multiplies the clock by 2.5 and doesn't care if it's 1000base-X or SGMII. With your patches we might even be able to use in-band autonegoation for 10,100 and 1000Mbps and then just disable it for 2.5Gbps. I need to test it, but I have hope that this should work. Regards, Stefan
