Since the referenced commit, changing the MTU on a running interface no longer disconnects and reconnects the PHY; __stmmac_release() merely stops phylink, which also suspends the PHY (BMCR power-down) when WoL is not enabled. __stmmac_open() then performs the DMA software reset in stmmac_hw_setup() before phylink_start() resumes the PHY again. IEEE 802.3 22.2.4.1.5 allows a PHY to stop its receive clock while powered down, and stmmac requires a running receive clock for the DMA software reset to complete (the phylink config sets mac_requires_rxc). On such setups, e.g. the RK3566-based Home Assistant Green with an RTL8211F-VD PHY in RGMII mode, any runtime MTU change now times out and leaves the interface dead: rk_gmac-dwmac fe010000.ethernet end0: Failed to reset the dma rk_gmac-dwmac fe010000.ethernet end0: stmmac_hw_setup: DMA engine initialization failed rk_gmac-dwmac fe010000.ethernet end0: __stmmac_open: Hw setup failed rk_gmac-dwmac fe010000.ethernet end0: failed reopening the interface after MTU change In the field this is triggered by NetworkManager applying an MTU while activating the connection, breaking networking entirely. Resume the PHY in __stmmac_open() before the hardware setup, making it the counterpart of the phylink_stop() in __stmmac_release(), like stmmac_resume() already does for the same reason. phylink_start() also resumes the PHY, but only after stmmac_hw_setup(), and it cannot be moved before the hardware setup since it may bring the link up immediately from a workqueue, racing with the initialization (see the comment in stmmac_resume()). For the regular ndo_open path the PHY has just been attached and is not suspended, in which case phylink_prepare_resume() does nothing. Fixes: db299a0c09e9 ("net: stmmac: move PHY handling out of __stmmac_open()/release()") Link: https://github.com/home-assistant/operating-system/issues/4858 Signed-off-by: Stefan Agner --- Changes in v2: - Move the PHY resume from stmmac_change_mtu() into __stmmac_open() so that it also counters the PHY suspend caused by __stmmac_release() (suggested by Andrew Lunn), placed before stmmac_reset_queues_param() to match the ordering used in stmmac_resume() drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -4147,6 +4147,15 @@ dma_conf->tx_queue[i].tbs = priv->dma_conf.tx_queue[i].tbs; memcpy(&priv->dma_conf, dma_conf, sizeof(*dma_conf)); + /* The PHY is suspended when the interface is reopened without + * disconnecting the PHY, e.g. on MTU change. IEEE 802.3 allows PHYs + * to stop their receive clock while powered down, but the DMA + * software reset in stmmac_hw_setup() requires a running receive + * clock, and phylink_start() below resumes the PHY only after the + * hardware setup. Resume a suspended PHY here first. + */ + phylink_prepare_resume(priv->phylink); + stmmac_reset_queues_param(priv); ret = stmmac_hw_setup(dev); -- 2.49.0