net: phy: dp83869: fix STRAP_OPMODE bitmask

net: phy: dp83869: fix STRAP_OPMODE bitmask

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: 0eaf8ccf2047 ("net: phy: dp83869: Set opmode from straps")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Thanh Quan <thanh.quan.xn@renesas.com>
Signed-off-by: Hai Pham <hai.pham.ud@renesas.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org> # Port from U-Boot to Linux
Link: https://patch.msgid.link/20251027140320.8996-1-marek.vasut+renesas@mailbox.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>