netdev - [PATCH net-next 2/2] net: stmmac: thead: ensure divisor gives proper rate

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Message-Id: <E1tlToD-004W3g-HB@rmk-PC.armlinux.org.uk>
Date: Fri, 21 Feb 2025 14:15:17 +0000
From: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Drew Fustini <drew@...7.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Fu Wei <wefu@...hat.com>,
	Guo Ren <guoren@...nel.org>,
	Jakub Kicinski <kuba@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-riscv@...ts.infradead.org,
	linux-stm32@...md-mailman.stormreply.com,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net-next 2/2] net: stmmac: thead: ensure divisor gives proper
 rate

thead was checking that the stmmac_clk rate was a multiple of the
RGMII rates for 1G and 100M, but didn't check for 10M. Rather than
use this with hard-coded speeds, check that the calculated divisor
gives the required rate by multplying the transmit clock rate back
up to the stmmac clock rate and checking that it agrees.

Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
index f16fa341aadb..f9f2bd65959f 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
@@ -45,9 +45,6 @@
 #define  TXCLK_DIR_OUTPUT		FIELD_PREP(TXCLK_DIR_MASK, 0)
 #define  TXCLK_DIR_INPUT		FIELD_PREP(TXCLK_DIR_MASK, 1)
 
-#define GMAC_GMII_RGMII_RATE	125000000
-#define GMAC_MII_RATE		25000000
-
 struct thead_dwmac {
 	struct plat_stmmacenet_data *plat;
 	void __iomem *apb_base;
@@ -124,11 +121,6 @@ static void thead_dwmac_fix_speed(void *priv, int speed, unsigned int mode)
 	case PHY_INTERFACE_MODE_RGMII_RXID:
 	case PHY_INTERFACE_MODE_RGMII_TXID:
 		rate = clk_get_rate(plat->stmmac_clk);
-		if (!rate || rate % GMAC_GMII_RGMII_RATE != 0 ||
-		    rate % GMAC_MII_RATE != 0) {
-			dev_err(dwmac->dev, "invalid gmac rate %ld\n", rate);
-			return;
-		}
 
 		writel(0, dwmac->apb_base + GMAC_PLLCLK_DIV);
 
@@ -139,6 +131,10 @@ static void thead_dwmac_fix_speed(void *priv, int speed, unsigned int mode)
 		}
 
 		div = rate / tx_rate;
+		if (rate != tx_rate * div) {
+			dev_err(dwmac->dev, "invalid gmac rate %lu\n", rate);
+			return;
+		}
 
 		reg = FIELD_PREP(GMAC_PLLCLK_DIV_EN, 1) |
 		      FIELD_PREP(GMAC_PLLCLK_DIV_NUM, div);
-- 
2.30.2