Re: [PATCH net-next v9 2/5] net: spacemit: Add K1 Ethernet MAC

[Simon Horman <horms@kernel.org>]

On Fri, Sep 05, 2025 at 07:09:31PM +0800, Vivian Wang wrote:
> The Ethernet MACs found on SpacemiT K1 appears to be a custom design
> that only superficially resembles some other embedded MACs. SpacemiT
> refers to them as "EMAC", so let's just call the driver "k1_emac".
> 
> Supports RGMII and RMII interfaces. Includes support for MAC hardware
> statistics counters. PTP support is not implemented.
> 
> Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>
> Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
> Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
> Reviewed-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
> Tested-by: Junhui Liu <junhui.liu@pigmoral.tech>
> Tested-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>

...

> diff --git a/drivers/net/ethernet/spacemit/k1_emac.c b/drivers/net/ethernet/spacemit/k1_emac.c

...

> +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;
> +
> +	regmap_set_bits(priv->regmap_apmu,
> +			priv->regmap_apmu_offset + APMU_EMAC_CTRL_REG,
> +			AXI_SINGLE_ID);
> +
> +	/* Disable transmit and receive units */
> +	emac_wr(priv, MAC_RECEIVE_CONTROL, 0x0);
> +	emac_wr(priv, MAC_TRANSMIT_CONTROL, 0x0);
> +
> +	/* Enable MAC address 1 filtering */
> +	emac_wr(priv, MAC_ADDRESS_CONTROL, MREGBIT_MAC_ADDRESS1_ENABLE);
> +
> +	/* Zero initialize the multicast hash table */
> +	emac_wr(priv, MAC_MULTICAST_HASH_TABLE1, 0x0);
> +	emac_wr(priv, MAC_MULTICAST_HASH_TABLE2, 0x0);
> +	emac_wr(priv, MAC_MULTICAST_HASH_TABLE3, 0x0);
> +	emac_wr(priv, MAC_MULTICAST_HASH_TABLE4, 0x0);
> +
> +	/* Configure thresholds */
> +	emac_wr(priv, MAC_TRANSMIT_FIFO_ALMOST_FULL, DEFAULT_TX_ALMOST_FULL);
> +	emac_wr(priv, MAC_TRANSMIT_PACKET_START_THRESHOLD,
> +		DEFAULT_TX_THRESHOLD);
> +	emac_wr(priv, MAC_RECEIVE_PACKET_START_THRESHOLD, DEFAULT_RX_THRESHOLD);
> +
> +	/* 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);
> +	emac_wr(priv, MAC_FC_HIGH_PAUSE_TIME, DEFAULT_FC_PAUSE_TIME);
> +	emac_wr(priv, MAC_FC_PAUSE_LOW_THRESHOLD, 0);
> +
> +	/* RX IRQ mitigation */
> +	rxirq = EMAC_RX_FRAMES & MREGBIT_RECEIVE_IRQ_FRAME_COUNTER_MASK;
> +	rxirq |= (EMAC_RX_COAL_TIMEOUT
> +		  << MREGBIT_RECEIVE_IRQ_TIMEOUT_COUNTER_SHIFT) &
> +		 MREGBIT_RECEIVE_IRQ_TIMEOUT_COUNTER_MASK;

Probably this driver can benefit from using FIELD_PREP and FIELD_GET
in a number of places. In this case I think it would mean that
MREGBIT_RECEIVE_IRQ_TIMEOUT_COUNTER_SHIFT can be removed entirely.

> +
> +	rxirq |= MREGBIT_RECEIVE_IRQ_MITIGATION_ENABLE;
> +	emac_wr(priv, DMA_RECEIVE_IRQ_MITIGATION_CTRL, rxirq);

...

> +/* Returns number of packets received */
> +static int emac_rx_clean_desc(struct emac_priv *priv, int budget)
> +{
> +	struct net_device *ndev = priv->ndev;
> +	struct emac_rx_desc_buffer *rx_buf;
> +	struct emac_desc_ring *rx_ring;
> +	struct sk_buff *skb = NULL;
> +	struct emac_desc *rx_desc;
> +	u32 got = 0, skb_len, i;
> +	int status;
> +
> +	rx_ring = &priv->rx_ring;
> +
> +	i = rx_ring->tail;
> +
> +	while (budget--) {
> +		rx_desc = &((struct emac_desc *)rx_ring->desc_addr)[i];
> +
> +		/* Stop checking if rx_desc still owned by DMA */
> +		if (READ_ONCE(rx_desc->desc0) & RX_DESC_0_OWN)
> +			break;
> +
> +		dma_rmb();
> +
> +		rx_buf = &rx_ring->rx_desc_buf[i];
> +
> +		if (!rx_buf->skb)
> +			break;
> +
> +		got++;
> +
> +		dma_unmap_single(&priv->pdev->dev, rx_buf->dma_addr,
> +				 rx_buf->dma_len, DMA_FROM_DEVICE);
> +
> +		status = emac_rx_frame_status(priv, rx_desc);
> +		if (unlikely(status == RX_FRAME_DISCARD)) {
> +			ndev->stats.rx_dropped++;

As per the comment in struct net-device,
ndev->stats should not be used in modern drivers.

Probably you want to implement NETDEV_PCPU_STAT_TSTATS.

Sorry for not mentioning this in an earlier review of
stats in this driver.

> +			dev_kfree_skb_irq(rx_buf->skb);
> +			rx_buf->skb = NULL;
> +		} else {
> +			skb = rx_buf->skb;
> +			skb_len = rx_frame_len(rx_desc) - ETH_FCS_LEN;
> +			skb_put(skb, skb_len);
> +			skb->dev = ndev;
> +			ndev->hard_header_len = ETH_HLEN;
> +
> +			skb->protocol = eth_type_trans(skb, ndev);
> +
> +			skb->ip_summed = CHECKSUM_NONE;
> +
> +			napi_gro_receive(&priv->napi, skb);
> +
> +			ndev->stats.rx_packets++;
> +			ndev->stats.rx_bytes += skb_len;
> +
> +			memset(rx_desc, 0, sizeof(struct emac_desc));
> +			rx_buf->skb = NULL;
> +		}
> +
> +		if (++i == rx_ring->total_cnt)
> +			i = 0;
> +	}
> +
> +	rx_ring->tail = i;
> +
> +	emac_alloc_rx_desc_buffers(priv);
> +
> +	return got;
> +}

...