linux-kernel - Re: [PATCH v3 net-next] net: ethernet: mtk_ppe

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Message-ID: <20250215140104.GO1615191@kernel.org>
Date: Sat, 15 Feb 2025 14:01:04 +0000
From: Simon Horman <horms@...nel.org>
To: Eric Woudstra <ericwouds@...il.com>
Cc: Jakub Kicinski <kuba@...nel.org>,
	Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>,
	Felix Fietkau <nbd@....name>, Sean Wang <sean.wang@...iatek.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Frank Wunderlich <frank-w@...lic-files.de>,
	Daniel Golle <daniel@...rotopia.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v3 net-next] net: ethernet: mtk_ppe_offload: Allow QinQ

On Wed, Feb 12, 2025 at 08:33:52PM +0100, Eric Woudstra wrote:
> 
> 
> On 2/12/25 1:51 AM, Jakub Kicinski wrote:
> > On Sun,  9 Feb 2025 12:09:36 +0100 Eric Woudstra wrote:
> >> This patch adds QinQ support to mtk_flow_offload_replace().
> >>
> >> Only PPPoE-in-Q (as before) and Q-in-Q are allowed. A combination
> >> of PPPoE and Q-in-Q is not allowed.
> > 
> > AFAIU the standard asks for outer tag in Q-in-Q to be ETH_P_8021AD,
> > but you still check:
> > 
> >> 			    act->vlan.proto != htons(ETH_P_8021Q))
> >> 				return -EOPNOTSUPP;
> > 
> > If this is a HW limitation I think you should document that more
> > clearly in the commit message. If you can fix it, I think you should..
> 
> It will be the first case. mtk_foe_entry_set_vlan() is limited to using
> only 1 fixed protocol. I'll drop the reviewed-by, amend the commit
> message and send v4.

I agree with Jakub's comment regarding the spec, and his suggested actions.
But, FWIIW, I also think that situations such as this are not uncommon in
the wild.