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 3988DC433EF for ; Tue, 26 Apr 2022 13:57:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348362AbiDZOAs (ORCPT ); Tue, 26 Apr 2022 10:00:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59556 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237966AbiDZOAr (ORCPT ); Tue, 26 Apr 2022 10:00:47 -0400 Received: from relay6-d.mail.gandi.net (relay6-d.mail.gandi.net [IPv6:2001:4b98:dc4:8::226]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8BB2E161E91; Tue, 26 Apr 2022 06:57:38 -0700 (PDT) Received: (Authenticated sender: maxime.chevallier@bootlin.com) by mail.gandi.net (Postfix) with ESMTPSA id 6E9B7C0009; Tue, 26 Apr 2022 13:57:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1650981457; 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=QXillSlDec+QdBFHMoazEsDlgZIJ8YMeOCBMwuPfphY=; b=brrKEe1cOheWxjqRfbu7MAq3yJXJavO8aHcrCe5VVAzM2yOYy/K/h+eccWo7D1Gl1mQh1g 34f6LXnicgZ6ZvQDxNlx+g81sODKX/Yj3vVznMa6DFjBbdvehpqOTjz82hhWV1z4LTRV52 g4bJUjcMPWLwrXoqSf7n1YlEgxAq7bQGgUwJhOYQgY+trLFNE09E0WnT47jnCcOqlhUjAC i2tnWLqwySW0S2F0GXg3Ob/uLVKU/Y6EVWYjG0FJoQC6zRRgUQt742stDIEqL7mHQIZmUe f4FziQHt4KpucEWziEjzQ3lW4+XeVtAG953iVobc/dUtKqa93uh/O9D3k3gKgA== Date: Tue, 26 Apr 2022 15:57:32 +0200 From: Maxime Chevallier To: Florian Fainelli 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 , Heiner Kallweit , Russell King , linux-arm-kernel@lists.infradead.org, Vladimir Oltean , Luka Perkov , Robert Marko Subject: Re: [PATCH net-next 2/5] net: dsa: add out-of-band tagging protocol Message-ID: <20220426155732.223e0446@pc-19.home> In-Reply-To: <68c4710d-013e-85e0-154d-413f4e13b27e@gmail.com> References: <20220422180305.301882-1-maxime.chevallier@bootlin.com> <20220422180305.301882-3-maxime.chevallier@bootlin.com> <68c4710d-013e-85e0-154d-413f4e13b27e@gmail.com> Organization: Bootlin X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.31; 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 Florian, On Fri, 22 Apr 2022 11:28:30 -0700 Florian Fainelli wrote: Thanks for the review :) > On 4/22/22 11:03, 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 tagging protocol relies on a new set of fields in skb->shinfo > > to transmit the dsa tagging information to and from the MAC driver. > > > > Signed-off-by: Maxime Chevallier > > First off, I am not a big fan of expanding skb::shared_info because > it is sensitive to cache line sizes and is critical for performance > at much higher speeds, I would expect Eric and Jakub to not be > terribly happy about it. No problem, I'm testing with the skb->cb approach as you suggested and see how it goes. > The Broadcom systemport (bcmsysport.c) has a mode where it can > extract the Broadcom tag and put it in front of the actual packet > contents which appears to be very similar here. From there on, you > can have two strategies: > > - have the Ethernet controller mangle the packet contents such that > the QCA tag is located in front of the actual Ethernet frame and > create a new tagging protocol variant for QCA, similar to the > TAG_BRCM versus TAG_BRCM_PREPEND > > - provide the necessary information for the tagger to work using an > out of band mechanism, which is what you have done, in which case, > maybe you can use skb->cb[] instead of using skb::shared_info? One of the reason why I chose the second is to support possible future cases where another controller would face a similar situation, and also make use of the out-of-band tagger. I understand that it's not very elegant in the sense that this breaks the nice tagging model we have, but adding/removing data before the payload also seems convoluted to achieve the same thing :) It seems that this approach comes with a bit of an overhead since it implies mangling the skb a bit, but I've yet to test this myself. That's actually what I wanted your opinion on, it also seems like Andrew likes the idea of putting the tag ahead of the frame to stick with the actual model. I don't have strong feelings myself on the way of doing this, I'm looking for an approach that is efficient but yet easily maintainable. Thanks, Maxime