[PATCH v3] net: spacemit: k1-emac: fix jumbo frame support

[Vivian Wang]

On 1/29/26 12:29, Tomas Hlavacek wrote:
> The driver never programs the MAC frame size and jabber registers,
> causing the hardware to reject frames larger than the default 1518
> bytes even when larger DMA buffers are allocated.
>
> Program MAC_MAXIMUM_FRAME_SIZE, MAC_TRANSMIT_JABBER_SIZE, and
> MAC_RECEIVE_JABBER_SIZE based on the configured MTU. Also fix the
> maximum buffer size from 4096 to 4095, since the descriptor buffer
> size field is only 12 bits. Account for double VLAN tags in frame
> size calculations.
>
> Fixes: bfec6d7f2001 ("net: spacemit: Add K1 Ethernet MAC")
> Cc: stable at vger.kernel.org
> Signed-off-by: Tomas Hlavacek <tmshlvck at gmail.com>
> ---
> v3:
> - Set all three frame/jabber registers, fix 12-bit buffer size field
>   overflow, use actual frame size with VLAN headroom consistently.
>
> v2: https://lore.kernel.org/netdev/20260126171449.83288-1-tmshlvck@gmail.com/
> - Added Fixes tag and Cc stable.
>
> v1: https://lore.kernel.org/netdev/20260126135919.77168-1-tmshlvck@gmail.com/
> ---
>  drivers/net/ethernet/spacemit/k1_emac.c | 21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/ethernet/spacemit/k1_emac.c b/drivers/net/ethernet/spacemit/k1_emac.c
> index 220eb5ce7583..cd6879d7434c 100644
> --- a/drivers/net/ethernet/spacemit/k1_emac.c
> +++ b/drivers/net/ethernet/spacemit/k1_emac.c
> @@ -12,6 +12,7 @@
>  #include <linux/dma-mapping.h>
>  #include <linux/etherdevice.h>
>  #include <linux/ethtool.h>
> +#include <linux/if_vlan.h>
>  #include <linux/interrupt.h>
>  #include <linux/io.h>
>  #include <linux/iopoll.h>
> @@ -38,7 +39,7 @@
>  
>  #define EMAC_DEFAULT_BUFSIZE		1536
>  #define EMAC_RX_BUF_2K			2048
> -#define EMAC_RX_BUF_4K			4096
> +#define EMAC_RX_BUF_MAX			FIELD_MAX(RX_DESC_1_BUFFER_SIZE_1_MASK)
>  
>  /* Tuning parameters from SpacemiT */
>  #define EMAC_TX_FRAMES			64
> @@ -202,8 +203,7 @@ static void emac_init_hw(struct emac_priv *priv)
>  {
>  	/* Destination address for 802.3x Ethernet flow control */
>  	u8 fc_dest_addr[ETH_ALEN] = { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x01 };
> -
> -	u32 rxirq = 0, dma = 0;
> +	u32 rxirq = 0, dma = 0, frame_sz;
>  
>  	regmap_set_bits(priv->regmap_apmu,
>  			priv->regmap_apmu_offset + APMU_EMAC_CTRL_REG,
> @@ -228,6 +228,15 @@ 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 MTU,
> +	 * accounting for Ethernet header, double VLAN tags, and FCS.
> +	 */
> +	frame_sz = priv->ndev->mtu + ETH_HLEN + 2 * VLAN_HLEN + ETH_FCS_LEN;
> +
> +	emac_wr(priv, MAC_MAXIMUM_FRAME_SIZE, frame_sz);
> +	emac_wr(priv, MAC_TRANSMIT_JABBER_SIZE, frame_sz);
> +	emac_wr(priv, MAC_RECEIVE_JABBER_SIZE, frame_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);
> @@ -924,14 +933,14 @@ static int emac_change_mtu(struct net_device *ndev, int mtu)
>  		return -EBUSY;
>  	}
>  
> -	frame_len = mtu + ETH_HLEN + ETH_FCS_LEN;
> +	frame_len = mtu + ETH_HLEN + 2 * VLAN_HLEN + ETH_FCS_LEN;
>  
>  	if (frame_len <= EMAC_DEFAULT_BUFSIZE)
>  		priv->dma_buf_sz = EMAC_DEFAULT_BUFSIZE;
>  	else if (frame_len <= EMAC_RX_BUF_2K)
>  		priv->dma_buf_sz = EMAC_RX_BUF_2K;
>  	else
> -		priv->dma_buf_sz = EMAC_RX_BUF_4K;
> +		priv->dma_buf_sz = EMAC_RX_BUF_MAX;
>  
>  	ndev->mtu = mtu;
>  
> @@ -2005,7 +2014,7 @@ static int emac_probe(struct platform_device *pdev)
>  	ndev->hw_features = NETIF_F_SG;
>  	ndev->features |= ndev->hw_features;
>  
> -	ndev->max_mtu = EMAC_RX_BUF_4K - (ETH_HLEN + ETH_FCS_LEN);
> +	ndev->max_mtu = EMAC_RX_BUF_MAX - (ETH_HLEN + 2 * VLAN_HLEN + ETH_FCS_LEN);
>  	ndev->pcpu_stat_type = NETDEV_PCPU_STAT_DSTATS;
>  
>  	priv = netdev_priv(ndev);

Thanks for the fix. This essentially matches what I've been testing as well.

Reviewed-by: Vivian Wang <wangruikang at iscas.ac.cn>