| 1 Jun 2025 |
 emily | so the tl;dr is that you have to explicitly specify 2500BASE-X on the host end for the PCS on the R4? | 12:44:20 |
| emily | to have it talk that to an SFP+? | 12:44:29 |
| emily | and then the other patchset hopefully makes that work? | 12:44:42 |
 K900 | In most cases it doesn't matter because you're either speaking GMII whatever to the module and then that's running at its own rate | 12:44:46 |
| K900 | But specifically for base2500-x it kinda matters because base2500-x is supposed to be dumb | 12:44:58 |
| K900 | EXCEPT WHEN IT'S NOT etc | 12:45:03 |
| emily | right… | 12:45:09 |
| K900 | Basically it depends on what your module is doing | 12:45:40 |
| emily | I remember you saying a few days ago that SGMII encompasses 2.5G. am I right to think that "2.5G SGMII" is that HSGMII or whatever you were talking about and that's distinct from 2500BASE-X? | 12:45:46 |
| K900 | Yes | 12:45:55 |
| K900 | Though SGMII doesn' | 12:46:00 |
| K900 | t | 12:46:00 |
| K900 | Ugh | 12:46:05 |
| K900 | I think what I was saying is that there's two PCS | 12:46:11 |
| K900 | One for SGMII and one for USXGMII | 12:46:20 |
| K900 | But | 12:46:21 |
| K900 | 2500base-x is also handled by the "SGMII" PCS | 12:46:30 |
| emily | I'm glad that this is confusing enough that even you don't understand what you say :D | 12:46:41 |
| K900 | Which technically makes it an SGMII/2500base-x combo PCS | 12:46:44 |
| K900 | Though it can also do 1000base-x | 12:46:59 |
| K900 | So it's technically an SGMII/2500base-x/1000base-x combo PCS | 12:47:08 |
| emily | okay so here's what the BCM84891L datasheet (https://datasheet4u.com/pdf-down/B/C/M/BCM84891L-Broadcom.pdf) says: "The BCM84891L supports the XFI/10GBASE-KR, USXGMII, 5000BASE-R, 2500BASE-R, 5000BASE-X, 2500BASE-X, and 1000BASE-X (SGMII) interface for connection to a MAC." | 12:47:19 |
| emily | do you know what I should take that to imply about how it's going to interface? | 12:47:29 |
| emily | "2.5G rate over USXGMII/XFI/2500BASE-R/2500BASE-X MAC interface" | 12:47:38 |
| emily | this is implying to me that it should be able to do the "dumb" passthrough? | 12:47:59 |
| emily | where the kernel can talk to the MAC directly? | 12:48:10 |
| K900 | I assume it's going to depend on some magic preset configuration | 12:48:21 |
| K900 | For a specific module | 12:48:25 |
| emily | right I'm not talking about the modules themselves | 12:48:37 |
| emily | I've sorta accepted I just have to keep gambling on those | 12:48:43 |
