net: bcmgenet: Workaround for Pi 4B network issue

Some combinations of Pi 4Bs and Ethernet switches don't reliably get a
DCHP-assigned IP address, leaving the unit with a self=assigned 169.254
address.

Forcing renegotiation has been found to be an effective workaround, so
add an automatic renegotiation after the link comes up for the first
time. For users and applications that need to minimise boot time,
add a module parameter (genet.force_reneg) to control the renegotiation
step - by default it is enabled.

See: raspberrypi#3108

Signed-off-by: Phil Elwell <phil@raspberrypi.org>

drivers/net/ethernet/broadcom/genet/bcmgenet.c

@@ -72,6 +72,10 @@
 #define GENET_RDMA_REG_OFF	(priv->hw_params->rdma_offset + \
 				TOTAL_DESC * DMA_DESC_SIZE)
 
+static bool force_reneg = true;
+module_param(force_reneg, bool, 0444);
+MODULE_PARM_DESC(force_reneg, "Force a renegotiation after the initial link-up");
+
 static inline void bcmgenet_writel(u32 value, void __iomem *offset)
 {
 	/* MIPS chips strapped for BE will automagically configure the
@@ -2610,6 +2614,7 @@ static void bcmgenet_irq_task(struct work_struct *work)
 	unsigned int status;
 	struct bcmgenet_priv *priv = container_of(
 			work, struct bcmgenet_priv, bcmgenet_irq_work);
+	static int first_link = 1;
 
 	netif_dbg(priv, intr, priv->dev, "%s\n", __func__);
 
@@ -2622,6 +2627,23 @@ static void bcmgenet_irq_task(struct work_struct *work)
 	if (status & UMAC_IRQ_LINK_EVENT) {
 		priv->dev->phydev->link = !!(status & UMAC_IRQ_LINK_UP);
 		phy_mac_interrupt(priv->dev->phydev);
+
+		if (priv->dev->phydev->link && first_link) {
+			first_link = 0;
+			/*
+			 * HACK: Some Pi4Bs, when paired with some switches,
+			 * come up in a strange state where they are unable to
+			 * transmit, causing them to fail to get an IP address.
+			 * Although the failure mechanism is not yet understood,
+			 * forcing renegotiation at this point has been shown
+			 * to be effective in avoiding the problem.
+			 */
+			if (force_reneg) {
+				dev_info(&priv->pdev->dev,
+					 "Forcing renegotiation\n");
+				genphy_restart_aneg(priv->dev->phydev);
+			}
+		}
 	}
 }