linux-kernel - Re: [PATCH net RESEND] net: ethernet: ti: am65-cpsw: Add IFF_UNICAST

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Date: Fri, 1 Mar 2024 17:49:57 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Ravi Gunasekaran <r-gunasekaran@...com>
Cc: Jakub Kicinski <kuba@...nel.org>,
	Sanjuán García, Jorge <Jorge.SanjuanGarcia@...gon.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"s-vadapalli@...com" <s-vadapalli@...com>,
	"rogerq@...nel.org" <rogerq@...nel.org>,
	"andrew@...n.ch" <andrew@...n.ch>,
	"f.fainelli@...il.com" <f.fainelli@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net RESEND] net: ethernet: ti: am65-cpsw: Add
 IFF_UNICAST_FLT flag to port device

On Fri, Mar 01, 2024 at 04:39:50PM +0530, Ravi Gunasekaran wrote:
> On 2/29/24 9:35 AM, Jakub Kicinski wrote:
> > On Wed, 28 Feb 2024 11:13:23 +0000 Sanjuán García, Jorge wrote:
> >> Since commit 8940e6b669ca ("net: dsa: avoid call to __dev_set_promiscuity()
> >> while rtnl_mutex isn't held") when conecting one of this switch's port
> >> to a DSA switch as the conduit interface, the network interface is set to
> >> promiscuous mode by default and cannot be set to not promiscuous mode again
> >> from userspace. The reason for this is that the cpsw ports net devices
> >> do not have the flag IFF_UNICAST_FLT set in their private flags.
> >>
> >> The cpsw switch should be able to set not promiscuous mode as otherwise
> >> a '1' is written to bit ALE_PORT_MACONLY_CAF which makes ethernet frames
> >> get an additional VLAN tag when entering the port connected to the DSA
> >> switch. Setting the IFF_UNICAST_FLT flag to all ports allows us to have
> >> the conduit interface on the DSA subsystem set as not promiscuous.
> > 
> > It doesn't look like am65-cpsw-nuss supports unicast filtering, 
> > tho, does it? So we're lying about support to work around some 
> > CPSW weirdness (additional VLAN tag thing)?
> 
> CPSW driver does not support unicast filtering. 

Then the driver can't declare IFF_UNICAST_FLT.

Why does enabling promiscuous mode cause Ethernet frames to get an
additional VLAN tag? 802.3 clause 4.2.4.1.1 Address recognition only
says "The MAC sublayer may also provide the capability of operating in
the promiscuous receive mode. In this mode of operation, the MAC
sublayer recognizes and accepts all valid frames, regardless of their
Destination Address field values.". Absolutely nothing about VLAN.