Re: [PATCH net 1/5] net: stmmac: Remove VLAN perfect matching dead code

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi Ovidiu,

On 7/29/26 11:51, Ovidiu Panait wrote:
> stmmac_vlan_update() falls back to "perfect matching" when the VLAN hash
> filter is unavailable (!priv->dma_cap.vlhash). This fallback has been
> unreachable in normal operation since its introduction in
> commit c7ab0b8088d7 ("net: stmmac: Fallback to VLAN Perfect filtering if
> HASH is not available") because the NETIF_F_HW_VLAN_{CTAG,STAG}_FILTER
> features are advertised only when priv->dma_cap.vlhash is true.
> 
> The fallback is also duplicating the code in vlan_add_hw_rx_fltr(), which
> is always available since stmmac_get_num_vlan() returns at least 1.

It's not exactly dead code, there's an stmmac selftest for that, see :

https://elixir.bootlin.com/linux/v7.2-rc4/source/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c#L973

It does exactly what you say, it fakes the fact that we don't support vlhash,
then exercise the perfect matching path.

But is it correct to drop that feature altogether ? Or should we just
relax the conditions for NETIF_F_HW_VLAN_{CTAG,STAG}_FILTER to be
advertised ?

Maxime