linux-kernel - RE: [PATCH v8 net-next 1/4] net: enetc: add Tx checksum offload for i.MX95 ENETC

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Message-ID:
 <PAXPR04MB85106BEF8ED9E4D373FEA46388052@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Wed, 18 Dec 2024 01:53:06 +0000
From: Wei Fang <wei.fang@....com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
CC: Claudiu Manoil <claudiu.manoil@....com>, Vladimir Oltean
	<vladimir.oltean@....com>, Clark Wang <xiaoning.wang@....com>,
	"andrew+netdev@...n.ch" <andrew+netdev@...n.ch>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	Frank Li <frank.li@....com>, "horms@...nel.org" <horms@...nel.org>,
	"idosch@...sch.org" <idosch@...sch.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>
Subject: RE: [PATCH v8 net-next 1/4] net: enetc: add Tx checksum offload for
 i.MX95 ENETC

> 
> From: Wei Fang <wei.fang@....com>
> Date: Fri, 13 Dec 2024 10:17:28 +0800
> 
> > In addition to supporting Rx checksum offload, i.MX95 ENETC also supports
> > Tx checksum offload. The transmit checksum offload is implemented through
> > the Tx BD. To support Tx checksum offload, software needs to fill some
> > auxiliary information in Tx BD, such as IP version, IP header offset and
> > size, whether L4 is UDP or TCP, etc.
> >
> > Same as Rx checksum offload, Tx checksum offload capability isn't defined
> > in register, so tx_csum bit is added to struct enetc_drvdata to indicate
> > whether the device supports Tx checksum offload.
> 
> [...]
> 
> > @@ -163,6 +184,30 @@ static int enetc_map_tx_buffs(struct enetc_bdr
> *tx_ring, struct sk_buff *skb)
> >  	dma_addr_t dma;
> >  	u8 flags = 0;
> >
> > +	enetc_clear_tx_bd(&temp_bd);
> > +	if (skb->ip_summed == CHECKSUM_PARTIAL) {
> > +		/* Can not support TSD and checksum offload at the same time */
> > +		if (priv->active_offloads & ENETC_F_TXCSUM &&
> > +		    enetc_tx_csum_offload_check(skb) && !tx_ring->tsd_enable) {
> > +			temp_bd.l3_aux0 = FIELD_PREP(ENETC_TX_BD_L3_START,
> > +						     skb_network_offset(skb));
> > +			temp_bd.l3_aux1 = FIELD_PREP(ENETC_TX_BD_L3_HDR_LEN,
> > +						     skb_network_header_len(skb) / 4);
> > +			temp_bd.l3_aux1 |= FIELD_PREP(ENETC_TX_BD_L3T,
> > +						      enetc_skb_is_ipv6(skb));
> > +			if (enetc_skb_is_tcp(skb))
> > +				temp_bd.l4_aux = FIELD_PREP(ENETC_TX_BD_L4T,
> > +							    ENETC_TXBD_L4T_TCP);
> > +			else
> > +				temp_bd.l4_aux = FIELD_PREP(ENETC_TX_BD_L4T,
> > +							    ENETC_TXBD_L4T_UDP);
> > +			flags |= ENETC_TXBD_FLAGS_CSUM_LSO |
> ENETC_TXBD_FLAGS_L4CS;
> > +		} else {
> > +			if (skb_checksum_help(skb))
> 
> Why not
> 
> 		} else if (skb_checksum_help(skb)) {
> 
> ?

Okay, accept.
> 
> > +				return 0;
> > +		}
> > +	}
> > +
> >  	i = tx_ring->next_to_use;
> >  	txbd = ENETC_TXBD(*tx_ring, i);
> >  	prefetchw(txbd);
> > @@ -173,7 +218,6 @@ static int enetc_map_tx_buffs(struct enetc_bdr
> *tx_ring, struct sk_buff *skb)
> >
> >  	temp_bd.addr = cpu_to_le64(dma);
> >  	temp_bd.buf_len = cpu_to_le16(len);
> > -	temp_bd.lstatus = 0;
> 
> Why is this removed and how is this change related to the checksum offload?

temp_bd has been cleared at the beginning, so we don't need to clear
lstatus again.
+	enetc_clear_tx_bd(&temp_bd);

And lstatus and aux* fields are in the same union. Clearing the lstatus
field will clear the checksum offload auxiliary information previously set.

union {
	struct {
		u8 l3_aux0;
		u8 l3_aux1;
		u8 l4_aux;
		u8 flags;
	}; /* default layout */
	__le32 txstart;
	__le32 lstatus;
};

> 
> >
> >  	tx_swbd = &tx_ring->tx_swbd[i];
> >  	tx_swbd->dma = dma;
> > @@ -594,7 +638,7 @@ static netdev_tx_t enetc_start_xmit(struct sk_buff
> *skb,
> >  {
> >  	struct enetc_ndev_priv *priv = netdev_priv(ndev);
> >  	struct enetc_bdr *tx_ring;
> > -	int count, err;
> > +	int count;
> >
> >  	/* Queue one-step Sync packet if already locked */
> >  	if (skb->cb[0] & ENETC_F_TX_ONESTEP_SYNC_TSTAMP) {
> > @@ -627,11 +671,6 @@ static netdev_tx_t enetc_start_xmit(struct sk_buff
> *skb,
> >  			return NETDEV_TX_BUSY;
> >  		}
> >
> > -		if (skb->ip_summed == CHECKSUM_PARTIAL) {
> > -			err = skb_checksum_help(skb);
> > -			if (err)
> > -				goto drop_packet_err;
> > -		}
> >  		enetc_lock_mdio();
> >  		count = enetc_map_tx_buffs(tx_ring, skb);
> >  		enetc_unlock_mdio();
> > @@ -3274,6 +3313,7 @@ static const struct enetc_drvdata enetc_pf_data =
> {
> >
> >  static const struct enetc_drvdata enetc4_pf_data = {
> >  	.sysclk_freq = ENETC_CLK_333M,
> > +	.tx_csum = 1,
> 
> Maybe make it `bool tx_csum:1` instead of u8 and assign `true` here?

I think 'u8 tx_csum:1' is fine, we just need to change "1" to "true". After
all, 'u8 xxx:n' fields may be defined later.

> 
> >  	.pmac_offset = ENETC4_PMAC_OFFSET,
> >  	.eth_ops = &enetc4_pf_ethtool_ops,
> >  };
> > diff --git a/drivers/net/ethernet/freescale/enetc/enetc.h
> b/drivers/net/ethernet/freescale/enetc/enetc.h
> > index 72fa03dbc2dd..e82eb9a9137c 100644
> > --- a/drivers/net/ethernet/freescale/enetc/enetc.h
> > +++ b/drivers/net/ethernet/freescale/enetc/enetc.h
> > @@ -234,6 +234,7 @@ enum enetc_errata {
> >
> >  struct enetc_drvdata {
> >  	u32 pmac_offset; /* Only valid for PSI which supports 802.1Qbu */
> > +	u8 tx_csum:1;
> >  	u64 sysclk_freq;
> >  	const struct ethtool_ops *eth_ops;
> >  };
> 
> Thanks,
> Olek