Hi Sean, On Fri, 7 Feb 2025 21:14:32 -0500 Sean Anderson <seanga2@xxxxxxxxx> wrote: > Hi Maxime, > > On 2/7/25 17:36, Maxime Chevallier wrote: > > Hello everyone, > > > > This series follows the 2 RFC that were sent a few weeks ago : > > RFC V2: https://lore.kernel.org/netdev/20250122174252.82730-1-maxime.chevallier@xxxxxxxxxxx/ > > RFC V1: https://lore.kernel.org/netdev/20241220201506.2791940-1-maxime.chevallier@xxxxxxxxxxx/ > > > > The goal of this series is to introduce an internal way of representing > > the "outputs" of ethernet devices, for now only focusing on PHYs. > > > > This allows laying the groundwork for multi-port devices support (both 1 > > PHY 2 ports, or more exotic setups with 2 PHYs in parallel, or MII > > multiplexers). > > > > Compared to the RFCs, this series tries to properly support SFP, > > especially PHY-driven SFPs through special phy_ports named "serdes" > > ports. They have the particularity of outputing a generic interface, > > that feeds into another component (usually, an SFP cage and therefore an > > SFP module). > > > > This allows getting a fairly generic PHY-driven SFP support (MAC-driven > > SFP is handled by phylink). > > > > This series doesn't address PHY-less interfaces (bare MAC devices, MACs > > with embedded PHYs not driven by phylink, or MAC connected to optical > > SFPs) to stay within the 15 patches limit, nor does it include the uAPI > > part that exposes these ports to userspace. > > > > I've kept the cover short, much more details can be found in the RFC > > covers. > > > > Thanks everyone, > > > > Maxime > > Forgive me for my ignorance, but why have a new ethtool interface instead of > extending ethtool_link_settings.port? It's a rather ancient interface, but it > seems to be tackling the exact same problem as you are trying to address. Older > NICs used to have several physical connectors (e.g. BNC, MII, twisted-pair) but > only one could be used at once. This seems directly analogous to a PHY that > supports multiple "port"s but not all at once. In fact, the only missing > connector type seems to be PORT_BACKPLANE. > > I can think of a few reasons why you wouldn't use PORT_*: > > - It describes the NIC and not the PHY, and perhaps there is too much impedance > mismatch? > - There is too much legacy in userspace (or in the kernel) to use that API in > this way? > - You need more flexibility? So there are multiple reasons that make the PORT_* field limited : - We can't gracefully handle multi-port PHYs for complex scenarios where we could say "I'm currently using the Copper port, but does the Fiber port has link ?" - As you mention in your first argument, what I'd like to try to do is come-up with a "generic" representation of outgoing NIC interfaces. The final use-cases I'd like to cover are multi-port NICs, allowing userspace to control which physical interfaces are available, and which t use. Looking at the hardware, this can be implemented in multiple ways : ___ Copper / MAC - PHY \__ SFP Here, a single PHY has 2 media-side interfaces, and we'd like to select the one to use. That's fairly common now, there are quite a number of PHYs that support this : mv33x3310, VSC8552, mv88x2222 only to name a few. But there are other, more uncommon topologies that exist : ____ SGMII PHY -- Copper / MAC - SGMII/1000BaseX MUX \____ SFP Here, we also have 2 media-side ports, but they are driver through different entities : The Copper port sits behind a single-port PHY, that is itself behind a *MII MUX, that's also connected to an SFP. Here the port selection is done at the MUX level Finally, I've been working on supporting devices whith another topology (actually, what started this whole work) : ___ PHY / MAC --MUX | \__ PHY Here both PHYs are on the same *MII bus, with some physical, gpio-driven MUX, and we have 2 PORT_TP on the same NIC. That design is used for link redundancy, if one PHY loses the link, we switch to the other one (that hopefully has link). All these cases have different drivers involved in the MUX'ing (phy driver itself, intermediate MUX in-between...), so the end-goal would be to expose to userspace info about the media interfaces themselves. This phy_port object would be what we expose to userspace. One missing step in this series is adding control on the ports (netlink API, enabling/disabling logic for ports) but that far exceeds the 15 patches limitation :) Sorry if all of that was blurry, I did make so good of a job linking to all previous discussions on the topic, I'll address that for the next round. Thanks, Maxime
