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

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Message-ID: <20260127020526-GYA88966@gentoo.org>
Date: Tue, 27 Jan 2026 10:05:26 +0800
From: Yixun Lan <dlan@...too.org>
To: Tomas Hlavacek <tmshlvck@...il.com>
Cc: netdev@...r.kernel.org, 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>,
	Vivian Wang <wangruikang@...as.ac.cn>
Subject: Re: [PATCH net v2] net: spacemit: k1-emac: program frame size
 registers for jumbo frames

Hi Tomas,

On 18:14 Mon 26 Jan     , 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);
> +
I'm no expert here, but just notice there is additional MAC_TRANSMIT_JABBER_SIZE
register which is no need to set? or is the problem on receive side only?

>  	/* 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
> 

-- 
Yixun Lan (dlan)