Re: [Patch RFC net-next 2/4] net: dsa: microchip: lan937x: remove vlan_filtering_is_global flag

[Vladimir Oltean <olteanv@gmail.com>]

On Fri, Jul 29, 2022 at 08:47:31PM +0530, Arun Ramadoss wrote:
> To have the similar implementation among the ksz switches, removed the
> vlan_filtering_is_global flag which is only present in the lan937x.
> 
> Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
> ---
>  drivers/net/dsa/microchip/lan937x_main.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/net/dsa/microchip/lan937x_main.c b/drivers/net/dsa/microchip/lan937x_main.c
> index daedd2bf20c1..9c1fe38efd1a 100644
> --- a/drivers/net/dsa/microchip/lan937x_main.c
> +++ b/drivers/net/dsa/microchip/lan937x_main.c
> @@ -401,11 +401,6 @@ int lan937x_setup(struct dsa_switch *ds)
>  		return ret;
>  	}
>  
> -	/* The VLAN aware is a global setting. Mixed vlan
> -	 * filterings are not supported.
> -	 */
> -	ds->vlan_filtering_is_global = true;
> -

You understand what this flag does, right? It ensures that if you have
lan0 and lan1 under VLAN-aware br0, then lan2 which is standalone will
declare NETIF_F_HW_VLAN_CTAG_FILTER. In turn, this makes the network
stack know that lan2 won't accept VLAN-tagged packets unless there is an
8021q interface with the given VID on top of it. This 8021q interface
calls vlan_vid_add() to populate the driver's VLAN RX filter with its
VID, and this gets translated into dsa_slave_vlan_rx_add_vid() which
ultimately reaches the driver's ->port_vlan_add() function.

If VLAN filtering *is* a global setting, and looking at this call from
ksz9477_port_vlan_filtering() which is not per port, I'd say it is:

		ksz_cfg(dev, REG_SW_LUE_CTRL_0, SW_VLAN_ENABLE, true);

then what would happen is that all VLAN tagged traffic would be dropped
on the standalone lan2.

I'd say that the ksz9477 is buggy for not declaring vlan_filtering_is_global,
rather than encouraging you to delete it from lan937x. In turn, fixing
ksz9477 would make setting this flag from a common location possible,
because ksz8 needs it too.