From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pidgin.makrotopia.org (pidgin.makrotopia.org [185.142.180.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0449D21CA02; Tue, 13 Jan 2026 14:22:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.142.180.65 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768314167; cv=none; b=tZsrc9d2wLZrP0NhLi0WlD7wrsBGDtkuAIxP3vzERj9m5O+BeGx5m4MGwK39MtcgZsyiq4s3r09upItckoh1gG272JNlHBtriAKIO6Zqe9AZpSOItLGRuGz7gfAztEdB8IwZSf4jqcwWbJJC5+UUFqpymCxB06HlSw9w8ufb3Cw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768314167; c=relaxed/simple; bh=45dZQdW9fGUa224LTS3tQ2Qsw+8kqQrF6HjLpsqqbfQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rde93hUFKgQVE6aTYusHwYea0UHaEdzQTn8RtNU5xekv6yUjCJXGOHxBzsOqBqpB7ZYPQxi3jzdF0UPkCdQpGp5cFkjPpud17r+CxHOW48NU0UDLLc2eDX1y6Djm9vcNBYXSBC06F4D+Yh7cJGfAFuuLWa6vbFxbWzPPK6h2+Fc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=makrotopia.org; spf=pass smtp.mailfrom=makrotopia.org; arc=none smtp.client-ip=185.142.180.65 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=makrotopia.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=makrotopia.org Received: from local by pidgin.makrotopia.org with esmtpsa (TLS1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.99) (envelope-from ) id 1vffHv-000000004Ng-1YDD; Tue, 13 Jan 2026 14:22:27 +0000 Date: Tue, 13 Jan 2026 14:22:24 +0000 From: Daniel Golle To: Andrew Lunn Cc: Felix Fietkau , John Crispin , Sean Wang , Lorenzo Bianconi , Bc-bocun Chen , Rex Lu , Mason-cw Chang , Andrew Lunn , "David S. Miller" , Vladimir Oltean , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Matthias Brugger , AngeloGioacchino Del Regno , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org Subject: Re: [PATCH net-next RFC] net: ethernet: mtk_eth_soc: support using non-MediaTek DSA switches Message-ID: References: <34647edacab660b4cabed9733d2d3ef22bc041ac.1768273593.git.daniel@makrotopia.org> <252d6877-d966-4d19-a38c-cc83ba908494@lunn.ch> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <252d6877-d966-4d19-a38c-cc83ba908494@lunn.ch> On Tue, Jan 13, 2026 at 03:00:18PM +0100, Andrew Lunn wrote: > On Tue, Jan 13, 2026 at 03:11:54AM +0000, Daniel Golle wrote: > > MediaTek's Ethernet Frame Engine is tailored for use with their > > switches. This broke checksum and VLAN offloading when attaching a > > DSA switch which does not use MediaTek special tag format. > > This has been seen before. The Freescale FEC has similar problems when > combined with a Marvell switch, it cannot find the IP header, and so > checksum offloading does not work. > > I thought we solved this be modifying the ndev->feature of the conduit > interface to disable such offloads. But i don't see such code. So i > must be remembering wrongly. > > This is assuming the frame engine respects these flags: > > /usr/sbin/ethtool -k enp2s0 > Features for enp2s0: > rx-checksumming: on > tx-checksumming: on > tx-checksum-ipv4: on > tx-checksum-ip-generic: off [fixed] > tx-checksum-ipv6: on > tx-checksum-fcoe-crc: off [fixed] > tx-checksum-sctp: off [fixed] > > When you combine a Marvell Ethernet interface with a Marvell switch > offloading works of course. So it probably does require some logic in > the MAC driver to determine if the switch is of the same vendor or > not. MediaTek folks also got back to me in a private message, confirming the issue and also clarifying that the length of the tag is the limiting factor. Every 4-byte tag can work, sizes other than 4 bytes cannot. As MediaTek's tag format includes the 802.1Q VLAN as part of the tag itself I suspect VLAN offloading will still need some extra care to work on non-MTK 4-byte tags (like RealTek 4B, for example)... > > > diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c > > index e68997a29191b..654b707ee27a1 100644 > > --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c > > +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c > > @@ -1459,6 +1459,26 @@ static void setup_tx_buf(struct mtk_eth *eth, struct mtk_tx_buf *tx_buf, > > } > > } > > > > +static bool mtk_uses_dsa(struct net_device *dev) > > +{ > > +#if IS_ENABLED(CONFIG_NET_DSA) > > + return netdev_uses_dsa(dev) && > > + dev->dsa_ptr->tag_ops->proto == DSA_TAG_PROTO_MTK; > > +#else > > + return false; > > +#endif > > I think the concept of determining if the switch is using a specific > tag in order to enable/disable acceleration should be generic. So i > would try to make this an helper in include/next/dsa.h. Any MAC driver > can then use it. Now that I know that the Ethernet driver should have 4 modes: - no DSA at all - DSA with MediaTek special tag - DSA with non-MediaTek but still 4 byte special tag -> VLAN offloading needs to be figured out - DSA with special tag size not equal to 4 bytes -> no checksum and no VLAN offloading > > > @@ -1531,7 +1551,7 @@ static void mtk_tx_set_dma_desc_v2(struct net_device *dev, void *txd, > > /* tx checksum offload */ > > if (info->csum) > > data |= TX_DMA_CHKSUM_V2; > > - if (mtk_is_netsys_v3_or_greater(eth) && netdev_uses_dsa(dev)) > > + if (mtk_is_netsys_v3_or_greater(eth) && mtk_uses_dsa(dev)) > > data |= TX_DMA_SPTAG_V3; > > This looks to be in the hot path. Do you really want to do this > evaluation on every frame? You can change the tag protocol via sysfs, > however, dsa_tree_change_tag_proto() will only allow you to change the > tag while the conduit interface is down. So it should be safe to look > at the tag protocol once during open, and cache the result somewhere > local, struct mtk_eth? That should avoid a few cache misses. +1 > > > @@ -3192,6 +3212,14 @@ static netdev_features_t mtk_fix_features(struct net_device *dev, > > } > > } > > > > + if ((features & NETIF_F_IP_CSUM) && > > + non_mtk_uses_dsa(dev)) > > + features &= ~NETIF_F_IP_CSUM; > > + > > + if ((features & NETIF_F_IPV6_CSUM) && > > + non_mtk_uses_dsa(dev)) > > + features &= ~NETIF_F_IPV6_CSUM; > > + > > > When is mtk_fix_features() actually called? I don't know without > looking at the core. You will want it when open is called, when the > tagging protocol is fixed. It's used as .ndo_fix_features operation, which is called by __netdev_update_features() at various occasions, and I'm not sure if it would be called as well when changing the tag protocol...