netdev - [PATCH] net: spacemit: k1-emac: program frame size registers for jumbo frames

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Message-ID: <20260126135919.77168-1-tmshlvck@gmail.com>
Date: Mon, 26 Jan 2026 14:59:19 +0100
From: Tomas Hlavacek <tmshlvck@...il.com>
To: netdev@...r.kernel.org
Cc: linux-riscv@...ts.infradead.org,
	spacemit@...ts.linux.dev,
	"David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Yixun Lan <dlan@...nel.org>,
	Vivian Wang <wangruikang@...as.ac.cn>,
	Tomas Hlavacek <tmshlvck@...il.com>
Subject: [PATCH] net: spacemit: k1-emac: program frame size registers for jumbo frames

The driver allows changing MTU up to 4K via emac_change_mtu() and
allocates appropriately sized DMA buffers, but it never programs the
MAC_MAXIMUM_FRAME_SIZE and MAC_RECEIVE_JABBER_SIZE registers.

This causes the MAC hardware to reject frames larger than the default
1518 bytes, even when larger buffers are allocated. Frames exceeding
the default size trigger jabber errors and are discarded.

Signed-off-by: Tomas Hlavacek <tmshlvck@...il.com>
---
 drivers/net/ethernet/spacemit/k1_emac.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/spacemit/k1_emac.c b/drivers/net/ethernet/spacemit/k1_emac.c
index 220eb5ce7583..31b1bdb2827e 100644
--- a/drivers/net/ethernet/spacemit/k1_emac.c
+++ b/drivers/net/ethernet/spacemit/k1_emac.c
@@ -228,6 +228,12 @@ static void emac_init_hw(struct emac_priv *priv)
 		DEFAULT_TX_THRESHOLD);
 	emac_wr(priv, MAC_RECEIVE_PACKET_START_THRESHOLD, DEFAULT_RX_THRESHOLD);
 
+	/* Set maximum frame size and jabber size based on configured buffer
+	 * size.
+	 */
+	emac_wr(priv, MAC_MAXIMUM_FRAME_SIZE, priv->dma_buf_sz);
+	emac_wr(priv, MAC_RECEIVE_JABBER_SIZE, priv->dma_buf_sz);
+
 	/* Configure flow control (enabled in emac_adjust_link() later) */
 	emac_set_mac_addr_reg(priv, fc_dest_addr, MAC_FC_SOURCE_ADDRESS_HIGH);
 	emac_wr(priv, MAC_FC_PAUSE_HIGH_THRESHOLD, DEFAULT_FC_FIFO_HIGH);
-- 
2.52.0