net: ftgmac100: Fix Aspeed ast2600 TX hang issue

The new HW arbitration feature on Aspeed ast2600 will cause MAC TX to
hang when handling scatter-gather DMA.  Disable the problematic feature
by setting MAC register 0x58 bit28 and bit27.

Fixes: 39bfab8 ("net: ftgmac100: Add support for DT phy-handle property")
Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/faraday/ftgmac100.c

@@ -1817,6 +1817,11 @@ static int ftgmac100_probe(struct platform_device *pdev)
 		priv->rxdes0_edorr_mask = BIT(30);
 		priv->txdes0_edotr_mask = BIT(30);
 		priv->is_aspeed = true;
+		/* Disable ast2600 problematic HW arbitration */
+		if (of_device_is_compatible(np, "aspeed,ast2600-mac")) {
+			iowrite32(FTGMAC100_TM_DEFAULT,
+				  priv->base + FTGMAC100_OFFSET_TM);
+		}
 	} else {
 		priv->rxdes0_edorr_mask = BIT(15);
 		priv->txdes0_edotr_mask = BIT(15);

drivers/net/ethernet/faraday/ftgmac100.h

@@ -169,6 +169,14 @@
 #define FTGMAC100_MACCR_FAST_MODE	(1 << 19)
 #define FTGMAC100_MACCR_SW_RST		(1 << 31)
 
+/*
+ * test mode control register
+ */
+#define FTGMAC100_TM_RQ_TX_VALID_DIS (1 << 28)
+#define FTGMAC100_TM_RQ_RR_IDLE_PREV (1 << 27)
+#define FTGMAC100_TM_DEFAULT                                                   \
+	(FTGMAC100_TM_RQ_TX_VALID_DIS | FTGMAC100_TM_RQ_RR_IDLE_PREV)
+
 /*
  * PHY control register
  */