Re: [PATCH net] net: amd-xgbe: support receiving packets with bad FCS

[David Laight <david.laight.linux@gmail.com>]

On Wed, 12 Aug 2026 09:16:16 +0000
James <aslan.jnn@gmail.com> wrote:

> From: James Nugraha <aslan.jnn@gmail.com>
> 
> The driver currently sets the MAC_RCR.DCRCC bit whenever RX is enabled.
> This disables hardware FCS validation, causing packets with a bad FCS to
> be accepted unconditionally. Users cannot control this behavior because
> the driver does not advertise NETIF_F_RXALL.

What actually happens to packets with bad FCS?
If FCS validation is actually disabled they'd get processed as valid packets.
That would be a serious bug.
OTOH the rx status could contain an 'fcs error' bit that causes the packet
be discarded and the software counts an error.
That would match the historic behaviour of many ethernet chips.

So neither the subject nor that text seems to be accurate.

With the bad packet (including its fcs) you can correct a single 18-bit error
burst - but I don't think anyone ever does that.

	David

> 
> Advertise NETIF_F_RXALL and disable it by default. Update DCRCC when the
> RXALL feature is enabled or disabled, and preserve the selected state
> across RX and link stop/start cycles.
> 
> Fixes: c5aa9e3b8156 ("amd-xgbe: Initial AMD 10GbE platform driver")
> Signed-off-by: James Nugraha <aslan.jnn@gmail.com>
> ---
> Tests:
> - Verified invalid-FCS packets are dropped with RXALL disabled.
> - Verified invalid-FCS packets are received with RXALL enabled.
> - Verified invalid-FCS packets are dropped again after RXALL is disabled.
> - Verified the RXALL setting survives RX stop/start.
> - Verified the RXALL setting survives link down/up.
> - Verified RXALL is disabled by default.
> 
>  drivers/net/ethernet/amd/xgbe/xgbe-dev.c  |  3 +--
>  drivers/net/ethernet/amd/xgbe/xgbe-drv.c  |  7 ++++++-
>  drivers/net/ethernet/amd/xgbe/xgbe-main.c |  7 +++++--
>  3 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-dev.c b/drivers/net/ethernet/amd/xgbe/xgbe-dev.c
> index 1f350d3bd..ad2030517 100644
> --- a/drivers/net/ethernet/amd/xgbe/xgbe-dev.c
> +++ b/drivers/net/ethernet/amd/xgbe/xgbe-dev.c
> @@ -3455,7 +3455,8 @@ static void xgbe_enable_rx(struct xgbe_prv_data *pdata)
>  	XGMAC_IOWRITE(pdata, MAC_RQC0R, reg_val);
>  
>  	/* Enable MAC Rx */
> -	XGMAC_IOWRITE_BITS(pdata, MAC_RCR, DCRCC, 1);
> +	XGMAC_IOWRITE_BITS(pdata, MAC_RCR, DCRCC,
> +			   !!(pdata->netdev->features & NETIF_F_RXALL));
>  	XGMAC_IOWRITE_BITS(pdata, MAC_RCR, CST, 1);
>  	XGMAC_IOWRITE_BITS(pdata, MAC_RCR, ACS, 1);
>  	XGMAC_IOWRITE_BITS(pdata, MAC_RCR, RE, 1);
> @@ -3466,7 +3467,6 @@ static void xgbe_disable_rx(struct xgbe_prv_data *pdata)
>  	unsigned int i;
>  
>  	/* Disable MAC Rx */
> -	XGMAC_IOWRITE_BITS(pdata, MAC_RCR, DCRCC, 0);
>  	XGMAC_IOWRITE_BITS(pdata, MAC_RCR, CST, 0);
>  	XGMAC_IOWRITE_BITS(pdata, MAC_RCR, ACS, 0);
>  	XGMAC_IOWRITE_BITS(pdata, MAC_RCR, RE, 0);
>  
> diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
> index 3a79fd054..5fb81bea1 100644
> --- a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
> +++ b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
> @@ -2247,13 +2247,14 @@ static int xgbe_set_features(struct net_device *netdev,
>  {
>  	struct xgbe_prv_data *pdata = netdev_priv(netdev);
>  	struct xgbe_hw_if *hw_if = &pdata->hw_if;
> -	netdev_features_t rxhash, rxcsum, rxvlan, rxvlan_filter;
> +	netdev_features_t rxhash, rxcsum, rxvlan, rxvlan_filter, rxall;
>  	int ret = 0;
>  
>  	rxhash = pdata->netdev_features & NETIF_F_RXHASH;
>  	rxcsum = pdata->netdev_features & NETIF_F_RXCSUM;
>  	rxvlan = pdata->netdev_features & NETIF_F_HW_VLAN_CTAG_RX;
>  	rxvlan_filter = pdata->netdev_features & NETIF_F_HW_VLAN_CTAG_FILTER;
> +	rxall = pdata->netdev_features & NETIF_F_RXALL;
>  
>  	if ((features & NETIF_F_RXHASH) && !rxhash)
>  		ret = hw_if->enable_rss(pdata);
> @@ -2284,6 +2285,10 @@ static int xgbe_set_features(struct net_device *netdev,
>  	else if (!(features & NETIF_F_HW_VLAN_CTAG_FILTER) && rxvlan_filter)
>  		hw_if->disable_rx_vlan_filtering(pdata);
>  
> +	if ((features & NETIF_F_RXALL) != rxall)
> +		XGMAC_IOWRITE_BITS(pdata, MAC_RCR, DCRCC,
> +				   !!(features & NETIF_F_RXALL));
> +
>  	pdata->netdev_features = features;
>  
>  	DBGPR("<--xgbe_set_features\n");
>  
> diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-main.c b/drivers/net/ethernet/amd/xgbe/xgbe-main.c
> index 0e8698928..898146b67 100644
> --- a/drivers/net/ethernet/amd/xgbe/xgbe-main.c
> +++ b/drivers/net/ethernet/amd/xgbe/xgbe-main.c
> @@ -351,7 +351,8 @@ int xgbe_config_netdev(struct xgbe_prv_data *pdata)
>  			      NETIF_F_GRO |
>  			      NETIF_F_HW_VLAN_CTAG_RX |
>  			      NETIF_F_HW_VLAN_CTAG_TX |
> -			      NETIF_F_HW_VLAN_CTAG_FILTER;
> +			      NETIF_F_HW_VLAN_CTAG_FILTER |
> +			      NETIF_F_RXALL;
>  
>  	if (pdata->hw_feat.rss)
>  		netdev->hw_features |= NETIF_F_RXHASH;
> @@ -382,2 +382,4 @@ int xgbe_config_netdev(struct xgbe_prv_data *pdata)
>  	netdev->features |= netdev->hw_features;
> +	/* disable RXALL by default */
> +	netdev->features &= ~NETIF_F_RXALL;
>  	pdata->netdev_features = netdev->features;
>