Re: [PATCH net v4 2/2] net: phy: mdio-i2c: defer RollBall bridge probe to PHY discovery

From: Maxime Chevallier <maxime.chevallier@bootlin.com>
To: Petr Wozniak <petr.wozniak@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	Andrew Lunn <andrew@lunn.ch>,
	Heiner Kallweit <hkallweit1@gmail.com>
Cc: Jakub Kicinski <kuba@kernel.org>,
	"David S . Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Paolo Abeni <pabeni@redhat.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-phy@lists.infradead.org, Bjorn Mork <bjorn@mork.no>,
	Aleksander Bajkowski <olek2@wp.pl>,
	Marek Behun <kabel@kernel.org>
Subject: Re: [PATCH net v4 2/2] net: phy: mdio-i2c: defer RollBall bridge probe to PHY discovery
Date: Fri, 26 Jun 2026 17:10:45 +0200	[thread overview]
Message-ID: <f729897a-c2a5-4925-9d8a-9d29569113ec@bootlin.com> (raw)
In-Reply-To: <20260624084814.20972-3-petr.wozniak@gmail.com>

Hi Petr,

On 6/24/26 10:48, Petr Wozniak wrote:
> commit 8fe125892f40 ("net: phy: sfp: probe for RollBall I2C-to-MDIO
> bridge in mdio-i2c") introduced a regression: the RollBall I2C-to-MDIO
> bridge is not yet ready to respond to CMD_READ/CMD_DONE cycles when
> sfp_sm_add_mdio_bus() runs in SFP_S_INIT.  The 200 ms probe times out,
> i2c_mii_probe_rollball() returns -ENODEV, and sfp_sm_add_mdio_bus()
> sets mdio_protocol = MDIO_I2C_NONE.  By the time sfp_sm_probe_for_phy()
> runs (up to ~17 s later on affected hardware), the bridge is fully
> initialized but PHY probing is skipped because the protocol has already
> been changed to NONE.
> 
> This affects both modules inserted before boot and hotplugged modules on
> hardware where bridge initialization exceeds the 200 ms probe window
> (confirmed: FLYPRO SFP-10GT-CS-30M with Aquantia AQR113C, hotplugged).
> 
> Move the probe from i2c_mii_init_rollball(), called at bus-creation time,
> to sfp_sm_probe_for_phy() in sfp.c, where it runs after the SFP state
> machine module initialization delays.  Export the probe function as
> mdio_i2c_probe_rollball() so sfp.c can call it.
> 
> For RTL8261BE-based modules the probe correctly returns -ENODEV at PHY
> discovery time, causing sfp_sm_probe_for_phy() to destroy the MDIO bus
> and set MDIO_I2C_NONE, eliminating the 5+ minute PHY probe retry loop.
> 
> For genuine RollBall modules (e.g. FLYPRO SFP-10GT-CS-30M with Aquantia
> AQR113C) the probe now runs after initialization is complete and
> correctly returns 0, so PHY detection proceeds normally.
> 
> Reported-by: Aleksander Bajkowski <olek2@wp.pl>
> Fixes: 8fe125892f40 ("net: phy: sfp: probe for RollBall I2C-to-MDIO bridge in mdio-i2c")
> Signed-off-by: Petr Wozniak <petr.wozniak@gmail.com>
I finally got time to test this with a RollBall module, and I
confirm what Aleksander says, the RollBall module's PHY doesn't
get detected even with this patch.

It does work on v7.0 though, so before the bridge probing was
introduced.

Maxime

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