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

[Stefan Agner <stefan@agner.ch>]

Hi Maxime,

On 2026-08-03 12:36, Maxime Chevallier wrote:
> 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>

Thanks for reviewing and testing!

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

It takes me quite a bit of time since I am not much into kernel
development (anymore). I'd appreciate if you can do it.

--
Stefan