Hello Russell, On 16/09/22 14:44, Russell King (Oracle) wrote: > On Fri, Sep 16, 2022 at 02:33:23PM +0530, Siddharth Vadapalli wrote: >> Hello Russell, >> >> On 16/09/22 12:50, Russell King (Oracle) wrote: >>> SGMII is designed for the setup in the diagram I provided in my previous >>> email. It is not designed for two MACs to talk direct to each other >>> without any ethernet PHY because of the asymmetric nature of the control >>> word. >>> >>> The PHY sends e.g. a control word of 0x9801 for 1G full duplex. On >>> reception of that, the MAC responds with 0x4001. Finally, the PHY >>> responds with 0xd801 to acknowledge the receipt of the MAC response. >>> >>> If both ends of the link are SGMII, both ends will be waiting for >>> the control word from a PHY which is not present, and the link will >>> not come up. >>> >>> 1000base-X is a symmetric protocol where both ends of the link >>> advertise their capabilities, acknowledge each others abilities and >>> resolve the duplex and pause settings. >>> >>> SGMII is a Cisco proprietary modification of 1000base-X designed for >>> communicating the results of media autonegotiation between an >>> ethernet PHY and ethernet MAC. >> >> I will try to implement and test SGMII mode in the conventional way with >> both the MAC and the PHY present. If I am unable to do so, I will revert >> to the current set of patches for the special case where the MAC >> emulates a PHY, and mention this setup in the commit message of the v2 >> series. I hope this approach would be fine to proceed with. Please let >> me know in case of any suggestions. > > What exact setups are you trying to support with this patch set? > > If you're looking to only add support for SGMII, then all you need > to do is to make sure it works with a PHY. Fixed-link in SGMII only > makes sense if you're directly connected to something like a network > switch, but even then, network switches tend to use 1000base-X in a > fixed-link mode rather than SGMII. I plan to support the standard MAC2PHY based SGMII mode. However, the SGMII ethernet PHY that I have with me has issues which is why I had tried the unconventional fixed-link SGMII mode with the MAC emulating the ethernet PHY. I will try to obtain a functional SGMII ethernet PHY and test the standard SGMII mode. Thank you for patiently answering my questions and helping me understand the SGMII mode better :) Regards, Siddharth.
