linux-kernel - [PATCH net v2] net: mdio: mdio-bcm-unimac: Correct rate fallback logic

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Message-Id: <20250730202533.3463529-1-florian.fainelli@broadcom.com>
Date: Wed, 30 Jul 2025 13:25:33 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: netdev@...r.kernel.org
Cc: Florian Fainelli <florian.fainelli@...adcom.com>,
	Doug Berger <opendmb@...il.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Jacob Keller <jacob.e.keller@...el.com>,
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH net v2] net: mdio: mdio-bcm-unimac: Correct rate fallback logic

When the parent clock is a gated clock which has multiple parents, the
clock provider (clk-scmi typically) might return a rate of 0 since there
is not one of those particular parent clocks that should be chosen for
returning a rate. Prior to ee975351cf0c ("net: mdio: mdio-bcm-unimac:
Manage clock around I/O accesses"), we would not always be passing a
clock reference depending upon how mdio-bcm-unimac was instantiated. In
that case, we would take the fallback path where the rate is hard coded
to 250MHz.

Make sure that we still fallback to using a fixed rate for the divider
calculation, otherwise we simply ignore the desired MDIO bus clock
frequency which can prevent us from interfacing with Ethernet PHYs
properly.

Fixes: ee975351cf0c ("net: mdio: mdio-bcm-unimac: Manage clock around I/O accesses")
Signed-off-by: Florian Fainelli <florian.fainelli@...adcom.com>
---
Changes in v2:

- provide additional details as to how a parent clock can have a rate of
  0 (Andrew)

- incorporate Simon's feedback that an optional clock is NULL and
  therefore returns a rate of 0 as well

 drivers/net/mdio/mdio-bcm-unimac.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/mdio/mdio-bcm-unimac.c b/drivers/net/mdio/mdio-bcm-unimac.c
index b6e30bdf5325..7baab230008a 100644
--- a/drivers/net/mdio/mdio-bcm-unimac.c
+++ b/drivers/net/mdio/mdio-bcm-unimac.c
@@ -209,10 +209,9 @@ static int unimac_mdio_clk_set(struct unimac_mdio_priv *priv)
 	if (ret)
 		return ret;
 
-	if (!priv->clk)
+	rate = clk_get_rate(priv->clk);
+	if (!rate)
 		rate = 250000000;
-	else
-		rate = clk_get_rate(priv->clk);
 
 	div = (rate / (2 * priv->clk_freq)) - 1;
 	if (div & ~MDIO_CLK_DIV_MASK) {
-- 
2.34.1