net: phy: Provide Module 4 KSZ9477 errata (DS80000754C)

The KSZ9477 errata points out (in 'Module 4') the link up/down problems
when EEE (Energy Efficient Ethernet) is enabled in the device to which
the KSZ9477 tries to auto negotiate.

The suggested workaround is to clear advertisement of EEE for PHYs in
this chip driver.

To avoid regressions with other switch ICs the new MICREL_NO_EEE flag
has been introduced.

Moreover, the in-register disablement of MMD_DEVICE_ID_EEE_ADV.MMD_EEE_ADV
MMD register is removed, as this code is both; now executed too late
(after previous rework of the PHY and DSA for KSZ switches) and not
required as setting all members of eee_broken_modes bit field prevents
the KSZ9477 from advertising EEE.

Fixes: 69d3b36 ("net: dsa: microchip: enable EEE support") # for KSZ9477
Signed-off-by: Lukasz Majewski <lukma@denx.de>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de> # Confirmed disabled EEE with oscilloscope.
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20230905093315.784052-1-lukma@denx.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Lukasz Majewski

drivers/net/dsa/microchip/ksz_common.c

@@ -2335,13 +2335,27 @@ static u32 ksz_get_phy_flags(struct dsa_switch *ds, int port)
 {
 	struct ksz_device *dev = ds->priv;
 
-	if (dev->chip_id == KSZ8830_CHIP_ID) {
+	switch (dev->chip_id) {
+	case KSZ8830_CHIP_ID:
 		/* Silicon Errata Sheet (DS80000830A):
 		 * Port 1 does not work with LinkMD Cable-Testing.
 		 * Port 1 does not respond to received PAUSE control frames.
 		 */
 		if (!port)
 			return MICREL_KSZ8_P1_ERRATA;
+		break;
+	case KSZ9477_CHIP_ID:
+		/* KSZ9477 Errata DS80000754C
+		 *
+		 * Module 4: Energy Efficient Ethernet (EEE) feature select must
+		 * be manually disabled
+		 *   The EEE feature is enabled by default, but it is not fully
+		 *   operational. It must be manually disabled through register
+		 *   controls. If not disabled, the PHY ports can auto-negotiate
+		 *   to enable EEE, and this feature can cause link drops when
+		 *   linked to another device supporting EEE.
+		 */
+		return MICREL_NO_EEE;
 	}
 
 	return 0;

drivers/net/phy/micrel.c

@@ -1800,9 +1800,6 @@ static const struct ksz9477_errata_write ksz9477_errata_writes[] = {
 	/* Transmit waveform amplitude can be improved (1000BASE-T, 100BASE-TX, 10BASE-Te) */
 	{0x1c, 0x04, 0x00d0},
 
-	/* Energy Efficient Ethernet (EEE) feature select must be manually disabled */
-	{0x07, 0x3c, 0x0000},
-
 	/* Register settings are required to meet data sheet supply current specifications */
 	{0x1c, 0x13, 0x6eff},
 	{0x1c, 0x14, 0xe6ff},
@@ -1847,6 +1844,12 @@ static int ksz9477_config_init(struct phy_device *phydev)
 			return err;
 	}
 
+	/* According to KSZ9477 Errata DS80000754C (Module 4) all EEE modes
+	 * in this switch shall be regarded as broken.
+	 */
+	if (phydev->dev_flags & MICREL_NO_EEE)
+		phydev->eee_broken_modes = -1;
+
 	err = genphy_restart_aneg(phydev);
 	if (err)
 		return err;

include/linux/micrel_phy.h

@@ -44,6 +44,7 @@
 #define MICREL_PHY_50MHZ_CLK	BIT(0)
 #define MICREL_PHY_FXEN		BIT(1)
 #define MICREL_KSZ8_P1_ERRATA	BIT(2)
+#define MICREL_NO_EEE		BIT(3)
 
 #define MICREL_KSZ9021_EXTREG_CTRL	0xB
 #define MICREL_KSZ9021_EXTREG_DATA_WRITE	0xC