linux-kernel - [PATCH net] net: phy: realtek: Reset after clock enable

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Message-Id: <20250704-phy-realtek-clock-fix-v1-1-63b33d204537@kernel.org>
Date: Fri, 04 Jul 2025 19:48:44 +0200
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, 
 Russell King <linux@...linux.org.uk>
Cc: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Florian Fainelli <florian.fainelli@...adcom.com>, 
 Detlev Casanova <detlev.casanova@...labora.com>, netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
 Sebastian Reichel <sebastian.reichel@...labora.com>
Subject: [PATCH net] net: phy: realtek: Reset after clock enable

On Radxa ROCK 4D boards we are seeing some issues with PHY detection and
stability (e.g. link loss, or not capable of transceiving packages)
after new board revisions switched from a dedicated crystal to providing
the 25 MHz PHY input clock from the SoC instead.

This board is using a RTL8211F PHY, which is connected to an always-on
regulator. Unfortunately the datasheet does not explicitly mention the
power-up sequence regarding the clock, but it seems to assume that the
clock is always-on (i.e. dedicated crystal).

By doing an explicit reset after enabling the clock, the issue on the
boards could no longer be observed.

Cc: stable@...r.kernel.org
Fixes: 7300c9b574cc ("net: phy: realtek: Add optional external PHY clock")
Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.com>
---
 drivers/net/phy/realtek/realtek_main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/phy/realtek/realtek_main.c b/drivers/net/phy/realtek/realtek_main.c
index c3dcb62574303374666b46a454cd4e10de455d24..3a783f0c3b4f2a4f6aa63a16ad309e3471b0932a 100644
--- a/drivers/net/phy/realtek/realtek_main.c
+++ b/drivers/net/phy/realtek/realtek_main.c
@@ -231,6 +231,10 @@ static int rtl821x_probe(struct phy_device *phydev)
 		return dev_err_probe(dev, PTR_ERR(priv->clk),
 				     "failed to get phy clock\n");

+	/* enabling the clock might produce glitches, so hard-reset the PHY */
+	phy_device_reset(phydev, 1);
+	phy_device_reset(phydev, 0);
+
 	ret = phy_read_paged(phydev, RTL8211F_PHYCR_PAGE, RTL8211F_PHYCR1);
 	if (ret < 0)
 		return ret;

---
base-commit: 4c06e63b92038fadb566b652ec3ec04e228931e8
change-id: 20250704-phy-realtek-clock-fix-6cd393e8cb2a

Best regards,
-- 
Sebastian Reichel <sre@...nel.org>