[PATCH net] net: dsa: mt7530: don't change PVC_EG_TAG when CPU port becomes VLAN-aware

[Paolo Abeni]

Hi,

On Mon, 2023-02-06 at 19:46 +0200, Vladimir Oltean wrote:
> On Mon, Feb 06, 2023 at 07:41:06PM +0300, Arınç ÜNAL wrote:
> > Finally I got time. It's been a seismically active day where I'm from.
> 
> My deepest condolences to those who experienced tragedies after today's
> earthquakes. A lot of people in neighboring countries are horrified
> thinking when this will happen to them. Hopefully you aren't living in
> Gaziantep or nearby cities.
> 
> > # ping 192.168.2.2
> > PING 192.168.2.2
> > [   39.508013] mtk_soc_eth 1b100000.ethernet eth1: dsa_switch_rcv: there is no metadata dst attached to skb 0xc2dfecc0
> > 
> > # ping 192.168.2.2
> > PING 192.168.2.2
> > [   22.674182] mtk_soc_eth 1b100000.ethernet eth1: mtk_poll_rx: received skb 0xc2d67840 without VLAN/DSA tag present
> 
> Thank you so much for testing. Would you mind cleaning everything up and
> testing with this patch instead (formatted on top of net-next)?
> Even if you need to adapt to your tree, hopefully you get the idea from
> the commit message.
> 
> From 218025fd0c33a06865e4202c5170bfc17e26cc75 Mon Sep 17 00:00:00 2001
> From: Vladimir Oltean <vladimir.oltean at nxp.com>
> Date: Mon, 6 Feb 2023 19:03:53 +0200
> Subject: [PATCH] net: ethernet: mtk_eth_soc: fix DSA TX tag hwaccel for switch
>  port 0
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> Arınç reports that on his MT7621AT Unielec U7621-06 board and MT7623NI
> Bananapi BPI-R2, packets received by the CPU over mt7530 switch port 0
> (of which this driver acts as the DSA master) are not processed
> correctly by software. More precisely, they arrive without a DSA tag
> (in packet or in the hwaccel area - skb_metadata_dst()), so DSA cannot
> demux them towards the switch's interface for port 0. Traffic from other
> ports receives a skb_metadata_dst() with the correct port and is demuxed
> properly.
> 
> Looking at mtk_poll_rx(), it becomes apparent that this driver uses the
> skb vlan hwaccel area:
> 
> 	union {
> 		u32		vlan_all;
> 		struct {
> 			__be16	vlan_proto;
> 			__u16	vlan_tci;
> 		};
> 	};
> 
> as a temporary storage for the VLAN hwaccel tag, or the DSA hwaccel tag.
> If this is a DSA master it's a DSA hwaccel tag, and finally clears up
> the skb VLAN hwaccel header.
> 
> I'm guessing that the problem is the (mis)use of API.
> skb_vlan_tag_present() looks like this:
> 
>  #define skb_vlan_tag_present(__skb)	(!!(__skb)->vlan_all)
> 
> So if both vlan_proto and vlan_tci are zeroes, skb_vlan_tag_present()
> returns precisely false. I don't know for sure what is the format of the
> DSA hwaccel tag, but I surely know that lowermost 3 bits of vlan_proto
> are 0 when receiving from port 0:
> 
> 	unsigned int port = vlan_proto & GENMASK(2, 0);
> 
> If the RX descriptor has no other bits set to non-zero values in
> RX_DMA_VTAG, then the call to __vlan_hwaccel_put_tag() will not, in
> fact, make the subsequent skb_vlan_tag_present() return true, because
> it's implemented like this:
> 
> static inline void __vlan_hwaccel_put_tag(struct sk_buff *skb,
> 					  __be16 vlan_proto, u16 vlan_tci)
> {
> 	skb->vlan_proto = vlan_proto;
> 	skb->vlan_tci = vlan_tci;
> }
> 
> What we need to do to fix this problem (assuming this is the problem) is
> to stop using skb->vlan_all as temporary storage for driver affairs, and
> just create some local variables that serve the same purpose, but
> hopefully better. Instead of calling skb_vlan_tag_present(), let's look
> at a boolean has_hwaccel_tag which we set to true when the RX DMA
> descriptors have something. Disambiguate based on netdev_uses_dsa()
> whether this is a VLAN or DSA hwaccel tag, and only call
> __vlan_hwaccel_put_tag() if we're certain it's a VLAN tag.
> 
> Link: https://lore.kernel.org/netdev/704f3a72-fc9e-714a-db54-272e17612637@arinc9.com/
> Fixes: 2d7605a72906 ("net: ethernet: mtk_eth_soc: enable hardware DSA untagging")
> Reported-by: Arınç ÜNAL <arinc.unal at arinc9.com>
> Signed-off-by: Vladimir Oltean <vladimir.oltean at nxp.com>

Thank you Vladimir for the quick turn-around! 

For future case, please avoid replying with new patches - tag area
included - to existing patch/thread, as it confuses tag propagation,
thanks!

Paolo