* [PATCH] net: phy: sfp: probe for RollBall I2C-to-MDIO bridge in mdio-i2c
[not found] <20260515115527.17241-1-petr.wozniak@gmail.com>
@ 2026-05-15 16:18 ` Petr Wozniak
2026-05-15 16:22 ` Petr Wozniak
0 siblings, 1 reply; 3+ messages in thread
From: Petr Wozniak @ 2026-05-15 16:18 UTC (permalink / raw)
To: netdev; +Cc: bjorn, andrew, linux-phy, Petr Wozniak
The "OEM"/"SFP-10G-T" quirk entry in sfp_fixup_rollball_cc()
unconditionally forces MDIO_I2C_ROLLBALL for all modules matching that
vendor/part-number combination. This works for modules that genuinely
implement a RollBall I2C-to-MDIO bridge, but silently breaks modules
that share the same EEPROM strings without having such a bridge.
The Realtek RTL8261BE-CG is one such module: a pure copper 10G SFP+
media converter with no I2C-to-MDIO bridge. Its EEPROM reports
vendor="OEM", part="SFP-10G-T-I", and -- critically -- Vendor OUI
00:00:00, making OUI-based differentiation impossible. With
MDIO_I2C_ROLLBALL the kernel stalls waiting for a PHY that never
appears:
sfp sfp2: probing phy device through the [MDIO_I2C_ROLLBALL] protocol
Move the probe into i2c_mii_init_rollball() in mdio-i2c.c, where the
RollBall protocol constants are already defined. After sending the
unlock password, issue a CMD_READ and wait ~70 ms for CMD_DONE. A
genuine RollBall bridge asserts CMD_DONE within that window; modules
without a bridge never do, so i2c_mii_init_rollball() returns -ENODEV.
sfp_i2c_mdiobus_create() treats -ENODEV as no PHY and falls back to
MDIO_I2C_NONE without creating an MDIO bus.
Add "OEM"/"SFP-10G-T-I" to the quirk table so RTL8261BE modules enter
the probe path; genuine RollBall modules continue to work as before.
Signed-off-by: Petr Wozniak <petr.wozniak@gmail.com>
---
Changes since v1:
- Moved probe from sfp.c into i2c_mii_probe_rollball() in mdio-i2c.c;
all RollBall protocol logic now lives in one place.
- Removed duplicated #define constants from sfp.c.
- sfp_i2c_mdiobus_create() handles -ENODEV from mdio_i2c_alloc()
and falls back to MDIO_I2C_NONE instead of failing the module probe.
- OEM/SFP-10G-T-I uses sfp_fixup_rollball (no CC byte correction
needed for a media converter).
drivers/net/mdio/mdio-i2c.c | 59 +++++++++++++++++++++++++++++++++----
drivers/net/phy/sfp.c | 8 ++++-
2 files changed, 60 insertions(+), 7 deletions(-)
diff --git a/drivers/net/mdio/mdio-i2c.c b/drivers/net/mdio/mdio-i2c.c
index da2001e..1973fda 100644
--- a/drivers/net/mdio/mdio-i2c.c
+++ b/drivers/net/mdio/mdio-i2c.c
@@ -352,6 +352,52 @@ static int i2c_mii_write_rollball(struct mii_bus *bus, int phy_id, int devad,
return 0;
}
+/*
+ * Probe for a RollBall I2C-to-MDIO bridge by issuing CMD_READ and waiting
+ * ~70 ms for CMD_DONE. Genuine RollBall bridges respond within that window.
+ * Modules that share the same EEPROM vendor/part strings but have no bridge
+ * (e.g. RTL8261BE pure copper media converter) never assert CMD_DONE, so
+ * -ENODEV is returned for them.
+ */
+static int i2c_mii_probe_rollball(struct i2c_adapter *i2c)
+{
+ u8 data_buf[] = { ROLLBALL_DATA_ADDR, 0x01, 0x00, 0x00 };
+ u8 cmd_buf[] = { ROLLBALL_CMD_ADDR, ROLLBALL_CMD_READ };
+ u8 cmd_addr = ROLLBALL_CMD_ADDR, result;
+ struct i2c_msg msgs[2];
+ int ret;
+
+ msgs[0].addr = ROLLBALL_PHY_I2C_ADDR;
+ msgs[0].flags = 0;
+ msgs[0].len = sizeof(data_buf);
+ msgs[0].buf = data_buf;
+ msgs[1].addr = ROLLBALL_PHY_I2C_ADDR;
+ msgs[1].flags = 0;
+ msgs[1].len = sizeof(cmd_buf);
+ msgs[1].buf = cmd_buf;
+
+ ret = i2c_transfer_rollball(i2c, msgs, ARRAY_SIZE(msgs));
+ if (ret)
+ return ret;
+
+ msleep(70);
+
+ msgs[0].addr = ROLLBALL_PHY_I2C_ADDR;
+ msgs[0].flags = 0;
+ msgs[0].len = 1;
+ msgs[0].buf = &cmd_addr;
+ msgs[1].addr = ROLLBALL_PHY_I2C_ADDR;
+ msgs[1].flags = I2C_M_RD;
+ msgs[1].len = 1;
+ msgs[1].buf = &result;
+
+ ret = i2c_transfer_rollball(i2c, msgs, ARRAY_SIZE(msgs));
+ if (ret)
+ return ret;
+
+ return result == ROLLBALL_CMD_DONE ? 0 : -ENODEV;
+}
+
static int i2c_mii_init_rollball(struct i2c_adapter *i2c)
{
struct i2c_msg msg;
@@ -372,10 +418,10 @@ static int i2c_mii_init_rollball(struct i2c_adapter *i2c)
ret = i2c_transfer(i2c, &msg, 1);
if (ret < 0)
return ret;
- else if (ret != 1)
+ if (ret != 1)
return -EIO;
- else
- return 0;
+
+ return i2c_mii_probe_rollball(i2c);
}
struct mii_bus *mdio_i2c_alloc(struct device *parent, struct i2c_adapter *i2c,
@@ -399,9 +445,10 @@ struct mii_bus *mdio_i2c_alloc(struct device *parent, struct i2c_adapter *i2c,
case MDIO_I2C_ROLLBALL:
ret = i2c_mii_init_rollball(i2c);
if (ret < 0) {
- dev_err(parent,
- "Cannot initialize RollBall MDIO I2C protocol: %d\n",
- ret);
+ if (ret != -ENODEV)
+ dev_err(parent,
+ "Cannot initialize RollBall MDIO I2C protocol: %d\n",
+ ret);
mdiobus_free(mii);
return ERR_PTR(ret);
}
diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
index 218c775..ce745b6 100644
--- a/drivers/net/phy/sfp.c
+++ b/drivers/net/phy/sfp.c
@@ -599,7 +599,8 @@ static const struct sfp_quirk sfp_quirks[] = {
SFP_QUIRK_S("TP-LINK", "TL-SM410U", sfp_quirk_oem_2_5g),
SFP_QUIRK_F("ETU", "ESP-T5-R", sfp_fixup_rollball_cc),
- SFP_QUIRK_F("OEM", "SFP-10G-T", sfp_fixup_rollball_cc),
+ SFP_QUIRK_F("OEM", "SFP-10G-T-I", sfp_fixup_rollball),
+ SFP_QUIRK_F("OEM", "SFP-10G-T", sfp_fixup_rollball_cc),
SFP_QUIRK_S("OEM", "SFP-2.5G-T", sfp_quirk_oem_2_5g),
SFP_QUIRK_S("OEM", "SFP-2.5G-BX10-D", sfp_quirk_2500basex),
SFP_QUIRK_S("OEM", "SFP-2.5G-BX10-U", sfp_quirk_2500basex),
@@ -802,6 +803,11 @@ static int sfp_i2c_mdiobus_create(struct sfp *sfp)
int ret;
i2c_mii = mdio_i2c_alloc(sfp->dev, sfp->i2c, sfp->mdio_protocol);
+ if (PTR_ERR_OR_ZERO(i2c_mii) == -ENODEV) {
+ /* RollBall probe found no bridge: no PHY on this module */
+ sfp->mdio_protocol = MDIO_I2C_NONE;
+ return 0;
+ }
if (IS_ERR(i2c_mii))
return PTR_ERR(i2c_mii);
--
2.51.0
^ permalink raw reply related [flat|nested] 3+ messages in thread