[PATCH v2] net: phy: dp83869: fix STRAP_OPMODE bitmask

[Marek Vasut]

From: Thanh Quan <thanh.quan.xn at renesas.com>

According to the TI DP83869HM datasheet Revision D (June 2025), section
7.6.1.41 STRAP_STS Register, the STRAP_OPMODE bitmask is bit [11:9].
Fix this.

In case the PHY is auto-detected via PHY ID registers, or not described
in DT, or, in case the PHY is described in DT but the optional DT property
"ti,op-mode" is not present, then the driver reads out the PHY functional
mode (RGMII, SGMII, ...) from hardware straps.

Currently, all upstream users of this PHY specify both DT compatible string
"ethernet-phy-id2000.a0f1" and ti,op-mode = <DP83869_RGMII_COPPER_ETHERNET>
property, therefore it seems no upstream users are affected by this bug.

The driver currently interprets bits [2:0] of STRAP_STS register as PHY
functional mode. Those bits are controlled by ANEG_DIS, ANEGSEL_0 straps
and an always-zero reserved bit. Systems that use RGMII-to-Copper functional
mode are unlikely to disable auto-negotiation via ANEG_DIS strap, or change
auto-negotiation behavior via ANEGSEL_0 strap. Therefore, even with this bug
in place, the STRAP_STS register content is likely going to be interpreted
by the driver as RGMII-to-Copper mode.

However, for a system with PHY functional mode strapping set to other mode
than RGMII-to-Copper, the driver is likely to misinterpret the strapping
as RGMII-to-Copper and misconfigure the PHY.

For example, on a system with SGMII-to-Copper strapping, the STRAP_STS
register reads as 0x0c20, but the PHY ends up being configured for
incompatible RGMII-to-Copper mode.

Fixes: f3e22eea815d ("net: phy: add TI DP83869HM ethernet driver")
Signed-off-by: Thanh Quan <thanh.quan.xn at renesas.com>
Signed-off-by: Hai Pham <hai.pham.ud at renesas.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas at mailbox.org> # Use FIELD_GET()
---
Cc: Dominic Rath <rath at ibv-augsburg.net>
Cc: Hai Pham <hai.pham.ud at renesas.com>
Cc: Jerome Forissier <jerome.forissier at linaro.org>
Cc: Joe Hershberger <joe.hershberger at ni.com>
Cc: Ramon Fried <rfried.dev at gmail.com>
Cc: Thanh Quan <thanh.quan.xn at renesas.com>
Cc: Tom Rini <trini at konsulko.com>
Cc: u-boot at lists.denx.de
---
V2: Update commit message to match Linux
---
 drivers/net/phy/dp83869.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/phy/dp83869.c b/drivers/net/phy/dp83869.c
index b6fb5adae1f..c60fbf26a03 100644
--- a/drivers/net/phy/dp83869.c
+++ b/drivers/net/phy/dp83869.c
@@ -5,6 +5,7 @@
  */
 
 #include <phy.h>
+#include <linux/bitfield.h>
 #include <linux/compat.h>
 #include <malloc.h>
 
@@ -64,7 +65,7 @@
 #define DP83869_RGMII_RX_CLK_DELAY_EN		BIT(0)
 
 /* STRAP_STS1 bits */
-#define DP83869_STRAP_OP_MODE_MASK		GENMASK(2, 0)
+#define DP83869_STRAP_OP_MODE_MASK		GENMASK(11, 9)
 #define DP83869_STRAP_STS1_RESERVED		BIT(11)
 #define DP83869_STRAP_MIRROR_ENABLED		BIT(12)
 
@@ -168,7 +169,7 @@ static int dp83869_set_strapped_mode(struct phy_device *phydev)
 	if (val < 0)
 		return val;
 
-	dp83869->mode = val & DP83869_STRAP_OP_MODE_MASK;
+	dp83869->mode = FIELD_GET(DP83869_STRAP_OP_MODE_MASK, val);
 
 	return 0;
 }
-- 
2.51.0