[RFC net-next v2 3/3] net: dsa: microchip: implement PHY loopback configuration for KSZ8794 and KSZ8873

From: Oleksij Rempel
Date: Tue Jan 09 2024 - 04:59:15 EST


Correct the PHY loopback bit handling in the ksz8_w_phy_bmcr and
ksz8_r_phy_bmcr functions for KSZ8794 and KSZ8873 variants in the ksz8795
driver. Previously, the code erroneously used Bit 7 of port register 0xD
for both chip variants, which is actually for LED configuration. This
update ensures the correct registers and bits are used for the PHY
loopback feature:

- For KSZ8794: Use 0xF / Bit 7.
- For KSZ8873: Use 0xD / Bit 0.

The lack of loopback support was seen on KSZ8873 system by using
"ethtool -t lanX". After this patch, the ethtool selftest will work,
but only if port is not part of a bridge.

Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
---
drivers/net/dsa/microchip/ksz8795.c | 36 ++++++++++++++++++++-----
drivers/net/dsa/microchip/ksz8795_reg.h | 1 +
2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/drivers/net/dsa/microchip/ksz8795.c b/drivers/net/dsa/microchip/ksz8795.c
index 51e0194453df..1d8377640a3d 100644
--- a/drivers/net/dsa/microchip/ksz8795.c
+++ b/drivers/net/dsa/microchip/ksz8795.c
@@ -731,16 +731,25 @@ static int ksz8_r_phy_bmcr(struct ksz_device *dev, u16 port, u16 *val)
if (ret)
return ret;

- if (restart & PORT_PHY_LOOPBACK)
- *val |= BMCR_LOOPBACK;
-
if (ctrl & PORT_FORCE_100_MBIT)
*val |= BMCR_SPEED100;

if (ksz_is_ksz88x3(dev)) {
+ if (restart & KSZ8873_PORT_PHY_LOOPBACK)
+ *val |= BMCR_LOOPBACK;
+
if ((ctrl & PORT_AUTO_NEG_ENABLE))
*val |= BMCR_ANENABLE;
} else {
+ u8 stat3;
+
+ ret = ksz_pread8(dev, port, REG_PORT_STATUS_3, &stat3);
+ if (ret)
+ return ret;
+
+ if (stat3 & PORT_PHY_LOOPBACK)
+ *val |= BMCR_LOOPBACK;
+
if (!(ctrl & PORT_AUTO_NEG_DISABLE))
*val |= BMCR_ANENABLE;
}
@@ -1001,8 +1010,7 @@ static int ksz8_w_phy_bmcr(struct ksz_device *dev, u16 port, u16 val)

restart = 0;
restart_mask = PORT_LED_OFF | PORT_TX_DISABLE | PORT_AUTO_NEG_RESTART |
- PORT_POWER_DOWN | PORT_AUTO_MDIX_DISABLE | PORT_FORCE_MDIX |
- PORT_PHY_LOOPBACK;
+ PORT_POWER_DOWN | PORT_AUTO_MDIX_DISABLE | PORT_FORCE_MDIX;

if (val & KSZ886X_BMCR_DISABLE_LED)
restart |= PORT_LED_OFF;
@@ -1022,8 +1030,22 @@ static int ksz8_w_phy_bmcr(struct ksz_device *dev, u16 port, u16 val)
if (val & KSZ886X_BMCR_FORCE_MDI)
restart |= PORT_FORCE_MDIX;

- if (val & BMCR_LOOPBACK)
- restart |= PORT_PHY_LOOPBACK;
+ if (ksz_is_ksz88x3(dev)) {
+ restart_mask |= KSZ8873_PORT_PHY_LOOPBACK;
+
+ if (val & BMCR_LOOPBACK)
+ restart |= KSZ8873_PORT_PHY_LOOPBACK;
+ } else {
+ u8 stat3 = 0;
+
+ if (val & BMCR_LOOPBACK)
+ stat3 |= PORT_PHY_LOOPBACK;
+
+ ret = ksz_prmw8(dev, port, REG_PORT_STATUS_3, PORT_PHY_LOOPBACK,
+ stat3);
+ if (ret)
+ return ret;
+ }

return ksz_prmw8(dev, port, regs[P_NEG_RESTART_CTRL], restart_mask,
restart);
diff --git a/drivers/net/dsa/microchip/ksz8795_reg.h b/drivers/net/dsa/microchip/ksz8795_reg.h
index beca974e0171..7c9341ef73b0 100644
--- a/drivers/net/dsa/microchip/ksz8795_reg.h
+++ b/drivers/net/dsa/microchip/ksz8795_reg.h
@@ -265,6 +265,7 @@
#define PORT_AUTO_MDIX_DISABLE BIT(2)
#define PORT_FORCE_MDIX BIT(1)
#define PORT_MAC_LOOPBACK BIT(0)
+#define KSZ8873_PORT_PHY_LOOPBACK BIT(0)

#define REG_PORT_1_STATUS_2 0x1E
#define REG_PORT_2_STATUS_2 0x2E
--
2.39.2