[PATCH v2 2/5] net: phy: realtek: simplify C22 reg access via MDIO_MMD_VEND2

Daniel Golle
2026-01-13T03:44:25Z

RealTek 2.5GE PHYs have all standard Clause-22 registers mapped also
inside MDIO_MMD_VEND2 at offset 0xa400. This is used mainly in case the
PHY is connected to a Clause-45-only bus. The RTL8221B is frequently
used in copper SFP module which uses the RollBall MDIO-over-I2C
method which *only* supports Clause-45, for example.

In order to support using the PHY on Clause-45-only busses, the PHY
driver has previously been split into a C22-only and C45-only instances,
creating quite a bit of redundancy and confusion.

In preparation of reunifying the two driver instances, add support for
translating MDIO_MMD_VEND2 registers 0xa400 to 0xa43c back to Clause-22
registers 0 to 30 in case the PHY is accessed on a Clause-22 bus.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
v2: improve commit message

drivers/net/phy/realtek/realtek_main.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/drivers/net/phy/realtek/realtek_main.c b/drivers/net/phy/realtek/realtek_main.c
index 18eea6b4b59a6..74980b2d66157 100644
--- a/drivers/net/phy/realtek/realtek_main.c
+++ b/drivers/net/phy/realtek/realtek_main.c
@@ -144,6 +144,7 @@

#define RTL822X_VND2_TO_PAGE(reg) ((reg) >> 4)
#define RTL822X_VND2_TO_PAGE_REG(reg) (16 + (((reg) & GENMASK(3, 0)) >> 1))
+#define RTL822X_VND2_TO_C22_REG(reg) (((reg) - 0xa400) / 2)
#define RTL822X_VND2_C22_REG(reg) (0xa400 + 2 * (reg))

#define RTL8221B_VND2_INER 0xa4d2
@@ -1265,6 +1266,11 @@ static int rtl822xb_read_mmd(struct phy_device *phydev, int devnum, u16 reg)
return mmd_phy_read(phydev->mdio.bus, phydev->mdio.addr,
phydev->is_c45, devnum, reg);

+ /* Simplify access to C22-registers addressed inside MDIO_MMD_VEND2 */
+ if (reg >= RTL822X_VND2_C22_REG(0) &&
+ reg <= RTL822X_VND2_C22_REG(30))
+ return __phy_read(phydev, RTL822X_VND2_TO_C22_REG(reg));
+
/* Use paged access for MDIO_MMD_VEND2 over Clause-22 */
page = RTL822X_VND2_TO_PAGE(reg);
oldpage = __phy_read(phydev, RTL821x_PAGE_SELECT);
@@ -1300,6 +1306,11 @@ static int rtl822xb_write_mmd(struct phy_device *phydev, int devnum, u16 reg,
return mmd_phy_write(phydev->mdio.bus, phydev->mdio.addr,
phydev->is_c45, devnum, reg, val);

+ /* Simplify access to C22-registers addressed inside MDIO_MMD_VEND2 */
+ if (reg >= RTL822X_VND2_C22_REG(0) &&
+ reg <= RTL822X_VND2_C22_REG(30))
+ return __phy_write(phydev, RTL822X_VND2_TO_C22_REG(reg), val);
+
/* Use paged access for MDIO_MMD_VEND2 over Clause-22 */
page = RTL822X_VND2_TO_PAGE(reg);
oldpage = __phy_read(phydev, RTL821x_PAGE_SELECT);
--
2.52.0