Re: [PATCH net v3] net: stmmac: resume PHY before hardware setup when opening the interface

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi Stefan,

On 8/3/26 11:51, Stefan Agner wrote:
> 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. The same
> regression has also been reported on i.MX8MP and reproduced on SoCFPGA
> based systems.
> 
> 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
> Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> Assisted-by: Claude:claude-fable-5
> Signed-off-by: Stefan Agner <stefan@agner.ch>

Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Do you feel confident following-up with the phylink renames, or should
I add that to my todolist ?

Thanks

Maxime