net: phy: broadcom: disable AutogrEEEn mode on BCM54xx

BCM54xx PHYs default to AutogrEEEn mode (MII_BUF_CNTL_0 bit 0), which
manages EEE Low Power Idle autonomously without forwarding LPI signaling
to the MAC over the RGMII interface.  This prevents the MAC from
tracking LPI activity and controlling TX LPI entry/exit.

Unconditionally clear the AutogrEEEn enable bit during config_init to
switch all BCM54xx PHYs to Native EEE mode.  In Native EEE mode the MAC
controls TX LPI and the PHY forwards received LPI on the RGMII
interface, allowing MACs with IEEE 802.3az support to observe RX LPI
transitions.

Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>

Author: nbuchwitz

drivers/net/phy/broadcom.c

@@ -490,6 +490,15 @@ static int bcm54xx_config_init(struct phy_device *phydev)
 	if (of_property_read_bool(np, "brcm,powerdown-enable"))
 		phydev->dev_flags |= PHY_BRCM_AUTO_PWRDWN_ENABLE;
 
+	/* Disable AutogrEEEn and switch to Native EEE mode so the MAC
+	 * can control LPI signaling and observe RX LPI on the RGMII
+	 * interface.
+	 */
+	err = bcm_phy_modify_exp(phydev, BCM54XX_TOP_MISC_MII_BUF_CNTL0,
+				 BCM54XX_MII_BUF_CNTL0_AUTOGREEEN_EN, 0);
+	if (err)
+		return err;
+
 	bcm54xx_adjust_rxrefclk(phydev);
 
 	switch (phydev->drv->phy_id & PHY_ID_MATCH_MODEL_MASK) {

include/linux/brcmphy.h

@@ -267,6 +267,9 @@
 #define BCM54XX_TOP_MISC_IDDQ_SD		(1 << 2)
 #define BCM54XX_TOP_MISC_IDDQ_SR		(1 << 3)
 
+#define BCM54XX_TOP_MISC_MII_BUF_CNTL0		(MII_BCM54XX_EXP_SEL_TOP + 0x00)
+#define  BCM54XX_MII_BUF_CNTL0_AUTOGREEEN_EN	BIT(0)
+
 #define BCM54XX_TOP_MISC_LED_CTL		(MII_BCM54XX_EXP_SEL_TOP + 0x0C)
 #define  BCM54XX_LED4_SEL_INTR			BIT(1)