From: Jakub Kicinski Date: Tue, 21 Oct 2025 00:17:22 +0000 (-0700) Subject: Merge branch 'net-stmmac-phylink-pcs-conversion' X-Git-Tag: v6.19-rc1~170^2~350 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6117dc5c88e455ecd4466fa8b5bcbbcb802a7744;p=thirdparty%2Fkernel%2Flinux.git Merge branch 'net-stmmac-phylink-pcs-conversion' Russell King says: ==================== net: stmmac: phylink PCS conversion This series is radical - it takes the brave step of ripping out much of the existing PCS support code and throwing it all away. I have discussed the introduction of the STMMAC_FLAG_HAS_INTEGRATED_PCS flag with Bartosz Golaszewski, and the conclusion I came to is that this is to workaround the breakage that I've been going on about concerning the phylink conversion for the last five or six years. The problem is that the stmmac PCS code manipulates the netif carrier state, which confuses phylink. There is a way of testing this out on the Jetson Xavier NX platform as the "PCS" code paths can be exercised while in RGMII mode - because RGMII also has in-band status and the status register is shared with SGMII. Testing this out confirms my long held theory: the interrupt handler manipulates the netif carrier state before phylink gets a look-in, which means that the mac_link_up() and mac_link_down() methods are never called, resulting in the device being non-functional. Moreover, on dwmac4 cores, ethtool reports incorrect information - despite having a full-duplex link, ethtool reports that it is half-dupex. Thus, this code is completely broken - anyone using it will not have a functional platform, and thus it doesn't deserve to live any longer, especially as it's a thorn in phylink. Rip all this out, leaving just the bare bones initialisation in place. However, this is not the last of what's broken. We have this hw->ps integer which is really not descriptive, and the DT property from which it comes from does little to help understand what's going on. Putting all the clues together: - early configuration of the GMAC configuration register for the speed. - setting the SGMII rate adapter layer to take its speed from the GMAC configuration register. Lastly, setting the transmit enable (TE) bit, which is a typo that puts the nail in the coffin of this code. It should be the transmit configuration (TC) bit. Given that when the link comes up, phylink will call mac_link_up() which will overwrite the speed in the GMAC configuration register, the only part of this that is functional is changing where the SGMII rate adapter layer gets its speed from, which is a boolean. From what I've found so far, everyone who sets the snps,ps-speed property which configures this mode also configures a fixed link, so the pre-configuration is unnecessary - the link will come up anyway. So, this series rips that out the preconfiguration as well, and replaces hw->ps with a boolean hw->reverse_sgmii_enable flag. We then move the sole PCS configuration into a phylink_pcs instance, which configures the PCS control register in the same way as is done during the probe function. Thus, we end up with much easier and simpler conversion to phylink PCS than previous attempts. Even so, this still results in inband mode always being enabled at the moment in the new .pcs_config() method to reflect what the probe function was doing. The next stage will be to change that to allow phylink to correctly configure the PCS. This needs fixing to allow platform glue maintainers who are currently blocked to progress. Please note, however, that this has not been tested with any SGMII platform. I've tried to get as many people into the Cc list with get_maintainers, I hope that's sufficient to get enough eyeballs on this. Changes since RFC: - new patch (7) to remove RGMII "pcs" mode - new patch (8) to move reverse "pcs" mode to stmmac_check_pcs_mode() - new patch (9) to simplify the code moved in the previous patch - new patch (10) to rename the confusing hw->ps to something more understandable. - new patch (11) to shut up inappropriate complaints about "snps,ps-speed" being invalid. - new patch (13) to add a MAC .pcs_init method, which will only be called when core has PCS present. - modify patch 14 to use this new pcs_init method. Despite getting a couple of responses to the RFC series posted in September, I have had nothing testing this on hardware. I have tested this on the Jetson Xavier NX, which included trial runs with enabling the RGMII "pcs" mode, hence the new patches that rip out this mode. I have come to the conclusion that the only way to get stmmac changes tested is to get them merged into net-next, thereby forcing people to have to run with them... and we'll deal with any fallout later. ==================== Link: https://patch.msgid.link/aPECqg0vZGnBFCbh@shell.armlinux.org.uk Signed-off-by: Jakub Kicinski --- 6117dc5c88e455ecd4466fa8b5bcbbcb802a7744