[PATCH v6 08/12] net: ethernet: mtk_eth_soc: fix RX data corruption issue

[Daniel Golle]

Also set bit 12 when setting up MAC MCR, as MediaTek SDK did the same
change stating:
"If without this patch, kernel might receive invalid packets that are
corrupted by GMAC."[1]
This fixes issues with <= 1G speed where we could previously observe
about 30% packet loss while the bad packet counter was increasing.
Unfortunately the meaning of bit 12 is not documented anywhere in SDK
code or datasheets.

[1]: https://git01.mediatek.com/plugins/gitiles/openwrt/feeds/mtk-openwrt-feeds/+/d8a2975939a12686c4a95c40db21efdc3f821f63
Tested-by: Bjørn Mork <bjorn@xxxxxxx>
Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 2 +-
 drivers/net/ethernet/mediatek/mtk_eth_soc.h | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 030d87c42bd4..fa61eefe0a61 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -615,7 +615,7 @@ static int mtk_mac_finish(struct phylink_config *config, unsigned int mode,
 	/* Setup gmac */
 	mcr_cur = mtk_r32(mac->hw, MTK_MAC_MCR(mac->id));
 	mcr_new = mcr_cur;
-	mcr_new |= MAC_MCR_IPG_CFG | MAC_MCR_FORCE_MODE |
+	mcr_new |= MAC_MCR_IPG_CFG | MAC_MCR_BIT_12 | MAC_MCR_FORCE_MODE |
 		   MAC_MCR_BACKOFF_EN | MAC_MCR_BACKPR_EN | MAC_MCR_FORCE_LINK;
 
 	/* Only update control register when needed! */
diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
index 142def8629c8..084d07c96c04 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
@@ -404,6 +404,7 @@
 #define MAC_MCR_FORCE_MODE	BIT(15)
 #define MAC_MCR_TX_EN		BIT(14)
 #define MAC_MCR_RX_EN		BIT(13)
+#define MAC_MCR_BIT_12		BIT(12)
 #define MAC_MCR_BACKOFF_EN	BIT(9)
 #define MAC_MCR_BACKPR_EN	BIT(8)
 #define MAC_MCR_FORCE_RX_FC	BIT(5)
-- 
2.39.1