[RFC PATCH net-next] net: ethernet: mediatek: support setting MTU

[DENG Qingfang <dqfext@gmail.com>]

MT762x HW supports frame length up to 2048 (maximum length on GDM),
so allow setting MTU up to 2030.

Signed-off-by: DENG Qingfang <dqfext@gmail.com>
---

I only tested this on MT7621, no sure if it is applicable for other SoCs
especially MT7628, which has an old IP.

---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 31 ++++++++++++++++++++-
 drivers/net/ethernet/mediatek/mtk_eth_soc.h | 11 ++++++--
 2 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 6d2d60675ffd..a0c56d9be1d5 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -353,7 +353,7 @@ static void mtk_mac_config(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_MAX_RX_1536 | MAC_MCR_IPG_CFG | MAC_MCR_FORCE_MODE |
+	mcr_new |= MAC_MCR_IPG_CFG | MAC_MCR_FORCE_MODE |
 		   MAC_MCR_BACKOFF_EN | MAC_MCR_BACKPR_EN | MAC_MCR_FORCE_LINK;
 
 	/* Only update control register when needed! */
@@ -2499,6 +2499,34 @@ static void mtk_uninit(struct net_device *dev)
 	mtk_rx_irq_disable(eth, ~0);
 }
 
+static int mtk_change_mtu(struct net_device *dev, int new_mtu)
+{
+	struct mtk_mac *mac = netdev_priv(dev);
+	u32 mcr_cur, mcr_new;
+	int length;
+
+	mcr_cur = mtk_r32(mac->hw, MTK_MAC_MCR(mac->id));
+	mcr_new = mcr_cur & ~MAC_MCR_MAX_RX_LEN_MASK;
+	length = new_mtu + MTK_RX_ETH_HLEN;
+
+	if (length <= 1518)
+		mcr_new |= MAC_MCR_MAX_RX_LEN(MAC_MCR_MAX_RX_LEN_1518);
+	else if (length <= 1536)
+		mcr_new |= MAC_MCR_MAX_RX_LEN(MAC_MCR_MAX_RX_LEN_1536);
+	else if (length <= 1552)
+		mcr_new |= MAC_MCR_MAX_RX_LEN(MAC_MCR_MAX_RX_LEN_1552);
+	else
+		mcr_new |= MAC_MCR_MAX_RX_LEN(MAC_MCR_MAX_RX_LEN_2048);
+
+	/* Only update control register when needed! */
+	if (mcr_new != mcr_cur)
+		mtk_w32(mac->hw, mcr_new, MTK_MAC_MCR(mac->id));
+
+	dev->mtu = new_mtu;
+
+	return 0;
+}
+
 static int mtk_do_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 {
 	struct mtk_mac *mac = netdev_priv(dev);
@@ -2795,6 +2823,7 @@ static const struct net_device_ops mtk_netdev_ops = {
 	.ndo_set_mac_address	= mtk_set_mac_address,
 	.ndo_validate_addr	= eth_validate_addr,
 	.ndo_do_ioctl		= mtk_do_ioctl,
+	.ndo_change_mtu		= mtk_change_mtu,
 	.ndo_tx_timeout		= mtk_tx_timeout,
 	.ndo_get_stats64        = mtk_get_stats64,
 	.ndo_fix_features	= mtk_fix_features,
diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
index 454cfcd465fd..cfc11654ccd6 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
@@ -17,12 +17,12 @@
 #include <linux/phylink.h>
 
 #define MTK_QDMA_PAGE_SIZE	2048
-#define	MTK_MAX_RX_LENGTH	1536
+#define MTK_MAX_RX_LENGTH	2048
 #define MTK_TX_DMA_BUF_LEN	0x3fff
 #define MTK_DMA_SIZE		256
 #define MTK_NAPI_WEIGHT		64
 #define MTK_MAC_COUNT		2
-#define MTK_RX_ETH_HLEN		(VLAN_ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN)
+#define MTK_RX_ETH_HLEN		(ETH_HLEN + ETH_FCS_LEN)
 #define MTK_RX_HLEN		(NET_SKB_PAD + MTK_RX_ETH_HLEN + NET_IP_ALIGN)
 #define MTK_DMA_DUMMY_DESC	0xffffffff
 #define MTK_DEFAULT_MSG_ENABLE	(NETIF_MSG_DRV | \
@@ -320,7 +320,12 @@
 
 /* Mac control registers */
 #define MTK_MAC_MCR(x)		(0x10100 + (x * 0x100))
-#define MAC_MCR_MAX_RX_1536	BIT(24)
+#define MAC_MCR_MAX_RX_LEN_MASK	GENMASK(25, 24)
+#define MAC_MCR_MAX_RX_LEN(_x)	(MAC_MCR_MAX_RX_LEN_MASK & ((_x) << 24))
+#define MAC_MCR_MAX_RX_LEN_1518	0x0
+#define MAC_MCR_MAX_RX_LEN_1536	0x1
+#define MAC_MCR_MAX_RX_LEN_1552	0x2
+#define MAC_MCR_MAX_RX_LEN_2048	0x3
 #define MAC_MCR_IPG_CFG		(BIT(18) | BIT(16))
 #define MAC_MCR_FORCE_MODE	BIT(15)
 #define MAC_MCR_TX_EN		BIT(14)
-- 
2.25.1