net: ethernet: mtk_eth_soc: drop packets to WDMA if the ring is full

Improves handling of DMA ring overflow.
Clarify other WDMA drop related comment.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20221116080734.44013-3-nbd@nbd.name
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -3425,9 +3425,12 @@ static int mtk_hw_init(struct mtk_eth *eth)
 	mtk_w32(eth, 0x21021000, MTK_FE_INT_GRP);
 
 	if (MTK_HAS_CAPS(eth->soc->caps, MTK_NETSYS_V2)) {
-		/* PSE should not drop port8 and port9 packets */
+		/* PSE should not drop port8 and port9 packets from WDMA Tx */
 		mtk_w32(eth, 0x00000300, PSE_DROP_CFG);
 
+		/* PSE should drop packets to port 8/9 on WDMA Rx ring full */
+		mtk_w32(eth, 0x00000300, PSE_PPE0_DROP);
+
 		/* PSE Free Queue Flow Control  */
 		mtk_w32(eth, 0x01fa01f4, PSE_FQFC_CFG2);
 

drivers/net/ethernet/mediatek/mtk_eth_soc.h

@@ -127,6 +127,7 @@
 #define PSE_FQFC_CFG1		0x100
 #define PSE_FQFC_CFG2		0x104
 #define PSE_DROP_CFG		0x108
+#define PSE_PPE0_DROP		0x110
 
 /* PSE Input Queue Reservation Register*/
 #define PSE_IQ_REV(x)		(0x140 + (((x) - 1) << 2))