From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18C84C433EF for ; Tue, 17 May 2022 06:54:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236599AbiEQGyI (ORCPT ); Tue, 17 May 2022 02:54:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48206 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235513AbiEQGyG (ORCPT ); Tue, 17 May 2022 02:54:06 -0400 Received: from relay9-d.mail.gandi.net (relay9-d.mail.gandi.net [217.70.183.199]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A82A126567; Mon, 16 May 2022 23:54:03 -0700 (PDT) Received: (Authenticated sender: maxime.chevallier@bootlin.com) by mail.gandi.net (Postfix) with ESMTPSA id 68338FF803; Tue, 17 May 2022 06:53:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1652770440; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LSRSBOWx0X3UM1Ake1VNIh+NUfX/y6+vqtFaURfJuPo=; b=IzCag1a/2/Oiqmxyp/nm3xkf4F2qFuTTBqkI3I9j44abhdGXKoOzszw2tDuUJr0sJCgOw4 hSTRCZ2qu+jSA/YAlXPprl6h7o97SxaybLE9dlvZ7VKTjAVODeTiSAbQmiv4Lt2n7K0bqE EbaCuMIJPWevm5/Oko/dQdJvZ7G8houWWIlPT8ZZFcetvVK52nK5mapuxjpuiYMXMuDSyX +TcbKy7YOyYlJnO1PEfUkGNxqWSUuQvMSHtqzayxPzdje+U76A6hc2psOjGap3KWZd3bpj HvARvrUJ0YXO8dSpf5W49+QaLWy8JjOOaO1VMFLQ1US96DeItNdgRZ+8bJeDeQ== Date: Tue, 17 May 2022 08:53:55 +0200 From: Maxime Chevallier To: Jakub Kicinski Cc: davem@davemloft.net, Rob Herring , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, thomas.petazzoni@bootlin.com, Andrew Lunn , Florian Fainelli , Heiner Kallweit , Russell King , linux-arm-kernel@lists.infradead.org, Vladimir Oltean , Luka Perkov , Robert Marko Subject: Re: [PATCH net-next v2 2/5] net: dsa: add out-of-band tagging protocol Message-ID: <20220517085355.4fab54b3@pc-20.home> In-Reply-To: <20220516122048.70e238a2@kernel.org> References: <20220514150656.122108-1-maxime.chevallier@bootlin.com> <20220514150656.122108-3-maxime.chevallier@bootlin.com> <20220516122048.70e238a2@kernel.org> Organization: Bootlin X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hello Jakub, On Mon, 16 May 2022 12:20:48 -0700 Jakub Kicinski wrote: > On Sat, 14 May 2022 17:06:53 +0200 Maxime Chevallier wrote: > > This tagging protocol is designed for the situation where the link > > between the MAC and the Switch is designed such that the Destination > > Port, which is usually embedded in some part of the Ethernet > > Header, is sent out-of-band, and isn't present at all in the > > Ethernet frame. > > > > This can happen when the MAC and Switch are tightly integrated on an > > SoC, as is the case with the Qualcomm IPQ4019 for example, where > > the DSA tag is inserted directly into the DMA descriptors. In that > > case, the MAC driver is responsible for sending the tag to the > > switch using the out-of-band medium. To do so, the MAC driver needs > > to have the information of the destination port for that skb. > > > > This out-of-band tagging protocol is using the very beggining of > > the skb headroom to store the tag. The drawback of this approch is > > that the headroom isn't initialized upon allocating it, therefore > > we have a chance that the garbage data that lies there at > > allocation time actually ressembles a valid oob tag. This is only > > problematic if we are sending/receiving traffic on the master port, > > which isn't a valid DSA use-case from the beggining. When dealing > > from traffic to/from a slave port, then the oob tag will be > > initialized properly by the tagger or the mac driver through the > > use of the dsa_oob_tag_push() call. > > > > Signed-off-by: Maxime Chevallier > > This must had been asked on v1 but there's no trace of it in the > current submission afaict... No you're correct, this wasn't explained. > If the tag is passed in the descriptor how is this not a pure > switchdev driver? The explanation must be preserved somehow. The main reason is that although the MAC and switch are rightly coupled on that platform, the switch is actually a QC8K that can live on it's own, as an external switch. Here, it's just a slightly modified version of this IP. The same goes for the MAC IP, but so far we don't support any other platform that have the MAC as a standalone controller. As far as we can tell, platforms that have this MAC also include a QCA8K, but the datasheet also mentions other modes (like outputing RGMII). Is this valid to have it as a standalone ethernet driver in that situation ? Thanks, Maxime