linux-kernel - Re: [PATCH net v2] net: spacemit: k1-emac: program frame size registers for jumbo frames

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Message-ID: <9f424b4e-b83b-47a0-8637-3df25e504be7@iscas.ac.cn>
Date: Tue, 27 Jan 2026 12:58:21 +0800
From: Vivian Wang <wangruikang@...as.ac.cn>
To: Tomas Hlavacek <tmshlvck@...il.com>, netdev@...r.kernel.org
Cc: linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 Yixun Lan <dlan@...nel.org>
Subject: Re: [PATCH net v2] net: spacemit: k1-emac: program frame size
 registers for jumbo frames

On 1/27/26 01:14, Tomas Hlavacek wrote:
> 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.
>
> Fixes: bfec6d7f2001 ("net: spacemit: Add K1 Ethernet MAC")
> Cc: stable@...r.kernel.org
> Signed-off-by: Tomas Hlavacek <tmshlvck@...il.com>
> ---
> v2: Added Fixes tag and Cc stable.
>
>  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);
> +

Oh and... maybe these should be priv->ndev->mtu + ETH_HLEN + ETH_FCS_LEN?