ag71xx: Fix rx ring buffer stall on small packets flood on qca956x and qca953x.

Backported from Code Aurora QSDK

Signed-off-by: Vittorio Gambaletta <openwrt@vittgam.net>

target/linux/ar71xx/files/arch/mips/ath79/dev-eth.c

@@ -996,6 +996,9 @@ void __init ath79_register_eth(unsigned int id)
 			pdata->reset_bit = AR934X_RESET_GE0_MAC |
 					   AR934X_RESET_GE0_MDIO;
 			pdata->set_speed = ar934x_set_speed_ge0;
+
+			if (ath79_soc == ATH79_SOC_QCA9533)
+				pdata->disable_inline_checksum_engine = 1;
 		} else {
 			pdata->reset_bit = AR934X_RESET_GE1_MAC |
 					   AR934X_RESET_GE1_MDIO;
@@ -1097,6 +1100,8 @@ void __init ath79_register_eth(unsigned int id)
 				pdata->set_speed = qca956x_set_speed_sgmii;
 			else
 				pdata->set_speed = ar934x_set_speed_ge0;
+
+			pdata->disable_inline_checksum_engine = 1;
 		} else {
 			pdata->reset_bit = QCA955X_RESET_GE1_MAC |
 					   QCA955X_RESET_GE1_MDIO;

target/linux/ar71xx/files/arch/mips/include/asm/mach-ath79/ag71xx_platform.h

@@ -37,7 +37,7 @@ struct ag71xx_platform_data {
 	u8		is_ar724x:1;
 	u8		has_ar8216:1;
 	u8		use_flow_control:1;
-	u8		is_qca956x:1;
+	u8		disable_inline_checksum_engine:1;
 
 	struct ag71xx_switch_platform_data *switch_data;
 

target/linux/ar71xx/files/drivers/net/ethernet/atheros/ag71xx/ag71xx_main.c

@@ -629,6 +629,22 @@ __ag71xx_link_adjust(struct ag71xx *ag, bool update)
 	ag71xx_wr(ag, AG71XX_REG_MAC_CFG2, cfg2);
 	ag71xx_wr(ag, AG71XX_REG_FIFO_CFG5, fifo5);
 	ag71xx_wr(ag, AG71XX_REG_MAC_IFCTL, ifctl);
+
+	if (pdata->disable_inline_checksum_engine) {
+		/*
+		 * The rx ring buffer can stall on small packets on QCA953x and
+		 * QCA956x. Disabling the inline checksum engine fixes the stall.
+		 * The wr, rr functions cannot be used since this hidden register
+		 * is outside of the normal ag71xx register block.
+		 */
+		void __iomem *dam = ioremap_nocache(0xb90001bc, 0x4);
+		if (dam) {
+			__raw_writel(__raw_readl(dam) & ~BIT(27), dam);
+			(void)__raw_readl(dam);
+			iounmap(dam);
+		}
+	}
+
 	ag71xx_hw_start(ag);
 
 	netif_carrier_on(ag->dev);