Re: [PATCH net v3 1/1] net: stmmac: Prevent DSA tags from breaking COE

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Mon, Jan 08, 2024 at 12:17:45PM +0100, Romain Gantois wrote:
> Some DSA tagging protocols change the EtherType field in the MAC header
> e.g.  DSA_TAG_PROTO_(DSA/EDSA/BRCM/MTK/RTL4C_A/SJA1105). On TX these tagged
> frames are ignored by the checksum offload engine and IP header checker of
> some stmmac cores.
> 
> On RX, the stmmac driver wrongly assumes that checksums have been computed
> for these tagged packets, and sets CHECKSUM_UNNECESSARY.
> 
> Add an additional check in the stmmac TX and RX hotpaths so that COE is
> deactivated for packets with ethertypes that will not trigger the COE and
> IP header checks.
> 
> Fixes: 6b2c6e4a938f ("net: stmmac: propagate feature flags to vlan")
> Cc: stable@vger.kernel.org
> Reported-by: Richard Tresidder <rtresidd@electromag.com.au>
> Link: https://lore.kernel.org/netdev/e5c6c75f-2dfa-4e50-a1fb-6bf4cdb617c2@electromag.com.au/
> Reported-by: Romain Gantois <romain.gantois@bootlin.com>
> Link: https://lore.kernel.org/netdev/c57283ed-6b9b-b0e6-ee12-5655c1c54495@bootlin.com/
> Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>
> ---

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>

>  .../net/ethernet/stmicro/stmmac/stmmac_main.c | 23 ++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index a9b6b383e863..6797c944a2ac 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -4371,6 +4371,19 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
>  	return NETDEV_TX_OK;
>  }
>  
> +/* Check if ethertype will trigger IP
> + * header checks/COE in hardware
> + */

Nitpick: you could render this in kernel-doc format.
https://docs.kernel.org/doc-guide/kernel-doc.html

> +static inline bool stmmac_has_ip_ethertype(struct sk_buff *skb)

Nitpick: in netdev it is preferred not to use the "inline" keyword at
all in C files, only "static inline" in headers, and to let the compiler
decide by itself when it is appropriate to inline the code (which it
does by itself even without the "inline" keyword). For a bit more
background why, you can view Documentation/process/4.Coding.rst, section
"Inline functions".

> +{
> +	int depth = 0;
> +	__be16 proto;
> +
> +	proto = __vlan_get_protocol(skb, eth_header_parse_protocol(skb), &depth);
> +
> +	return depth <= ETH_HLEN && (proto == htons(ETH_P_IP) || proto == htons(ETH_P_IPV6));
> +}