Re: [PATCH net v2 2/2] net: stmmac: Consider Tx VLAN offload tag length for maxSDU

[Jakub Kicinski <kuba@kernel.org>]

On Wed, 24 Sep 2025 10:24:44 +0530 G Thomas, Rohan wrote:
> >> Is the device adding the same VLAN tag twice if the proto is 8021AD?
> >> It looks like it from the code, but how every strange..
> >>
> >> In any case, it doesn't look like the driver is doing anything with
> >> the NETIF_F_HW_VLAN_* flags right? stmmac_vlan_insert() works purely
> >> off of vlan proto. So I think we should do the same thing here?  
> > 
> > I suppose the double tagging depends on the exact SKU but first check
> > looks unnecessary. Maybe stmmac_vlan_insert() should return the number
> > of vlans it decided to insert?
> >   
> 
> I overlooked the behavior of stmmac_vlan_insert(). It seems the hardware
> supports inserting only one VLAN tag at a time, with the default setting
> being SVLAN for 802.1AD and CVLAN for 802.1Q. I'll update the patch to
> simply add VLAN_HLEN when stmmac_vlan_insert() returns true. Please let
> me know if you have any further concerns.

SG, no further concerns.

Please make sure to CC "Ng, Boon Khai" <boon.khai.ng@altera.com>
who wrote the VLAN support (IIRC).