Re: [PATCH net] net: usb: lan78xx: disable VLAN filter in promiscuous mode

[Nicolai Buchwitz <nb@tipi-net.de>]

Hi Enrico

On 30.6.2026 16:15, Enrico Pozzobon via B4 Relay wrote:
> From: Enrico Pozzobon <enrico.pozzobon@dissecto.com>
> 
> The hardware VLAN filter (RFE_CTL_VLAN_FILTER_) drops VLAN-tagged 
> frames
> whose VID has not been registered via lan78xx_vlan_rx_add_vid(). It is
> left enabled in promiscuous mode, so packet capture (e.g. tcpdump or
> Wireshark) does not see tagged frames for unregistered VIDs.
> 
> Clear the filter while the interface is promiscuous and restore it from
> NETIF_F_HW_VLAN_CTAG_FILTER otherwise. Enforce the same condition in
> lan78xx_set_features() so netdev_update_features() cannot re-enable the
> filter while promiscuous.
> 
> Fixes: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 
> Ethernet device driver")
> Signed-off-by: Enrico Pozzobon <enrico.pozzobon@dissecto.com>
> ---
> Currently, on microchip lan7801, enabling promiscuous mode does not
> result in VLAN tagged packets being captured. This patch fixes this,
> forcing the RFE_CTL_VLAN_FILTER_ flag to be off when promiscuous mode 
> is
> enabled.
> ---
>  drivers/net/usb/lan78xx.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
> index c4cebacabcb5..a1a53ef85cb9 100644
> --- a/drivers/net/usb/lan78xx.c
> +++ b/drivers/net/usb/lan78xx.c
> @@ -1525,7 +1525,14 @@ static void lan78xx_set_multicast(struct 
> net_device *netdev)
>  	if (dev->net->flags & IFF_PROMISC) {
>  		netif_dbg(dev, drv, dev->net, "promiscuous mode enabled");
>  		pdata->rfe_ctl |= RFE_CTL_MCAST_EN_ | RFE_CTL_UCAST_EN_;
> +		/* bypass VLAN filter so all tagged frames are captured */
> +		pdata->rfe_ctl &= ~RFE_CTL_VLAN_FILTER_;
>  	} else {
> +		if (dev->net->features & NETIF_F_HW_VLAN_CTAG_FILTER)
> +			pdata->rfe_ctl |= RFE_CTL_VLAN_FILTER_;
> +		else
> +			pdata->rfe_ctl &= ~RFE_CTL_VLAN_FILTER_;
> +
>  		if (dev->net->flags & IFF_ALLMULTI) {
>  			netif_dbg(dev, drv, dev->net,
>  				  "receive all multicast enabled");
> @@ -3074,7 +3081,9 @@ static int lan78xx_set_features(struct net_device 
> *netdev,
>  	else
>  		pdata->rfe_ctl &= ~RFE_CTL_VLAN_STRIP_;
> 
> -	if (features & NETIF_F_HW_VLAN_CTAG_FILTER)
> +	/* keep VLAN filter off while promiscuous */
> +	if ((features & NETIF_F_HW_VLAN_CTAG_FILTER) &&
> +	    !(netdev->flags & IFF_PROMISC))
>  		pdata->rfe_ctl |= RFE_CTL_VLAN_FILTER_;
>  	else
>  		pdata->rfe_ctl &= ~RFE_CTL_VLAN_FILTER_;

nit: Could this be addressed as helper for both callers?

> [...]

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>

Thanks
Nicolai