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 919B0C43334 for ; Fri, 8 Jul 2022 00:44:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235567AbiGHAoM (ORCPT ); Thu, 7 Jul 2022 20:44:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49340 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229572AbiGHAoL (ORCPT ); Thu, 7 Jul 2022 20:44:11 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C16A670E44; Thu, 7 Jul 2022 17:44:10 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 7E2D8B824B5; Fri, 8 Jul 2022 00:44:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7E0EDC3411E; Fri, 8 Jul 2022 00:44:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1657241048; bh=EC7a4jTfAaizoRSMF4FsVpM10jc1Vx60by0MKMOikKI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=J7buxAjoy+adEYbK2ndgRVkdH/bRZQd1xQJ83dKqMYPLqzO7K8SohPXucoAmj7lJw lXlK98vnwsMtyUs6cqJvdncgZSM+u8iWNEd84GaJxGEb8JwmJznOQ8diA8yX3EE+9t AyBc2jtDAHiy/c9qalzH/C4zpxEfR44rctLToIM/H+o6DzxW+shjErAqPIZ51BH2Tj w3PhcIgxKUGzp6rfEjTCNkv8zm+iHrtWRB+8L8NEZ7Mv9xOAjzyEzGVOLdus18aNvi qFBhYl1bIalHBXubutm/9Fbfkaocgls6Zfa3BLkpbMVdpgT4B7+bPE8Q+LLXcKle9S rXNUZKZHDb9sw== Date: Thu, 7 Jul 2022 17:43:58 -0700 From: Jakub Kicinski To: Hans Schultz Cc: Vladimir Oltean , davem@davemloft.net, netdev@vger.kernel.org, Andrew Lunn , Vivien Didelot , Florian Fainelli , Eric Dumazet , Paolo Abeni , Jiri Pirko , Ivan Vecera , Roopa Prabhu , Nikolay Aleksandrov , Shuah Khan , Daniel Borkmann , Ido Schimmel , linux-kernel@vger.kernel.org, bridge@lists.linux-foundation.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH net-next 1/1] net: dsa: mv88e6xxx: allow reading FID when handling ATU violations Message-ID: <20220707174358.3b1b804a@kernel.org> In-Reply-To: <20220707102836.u7ig6rr2664mcrlf@skbuf> References: <20220706122502.1521819-1-netdev@kapio-technology.com> <20220707102836.u7ig6rr2664mcrlf@skbuf> 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 On Thu, 7 Jul 2022 13:28:36 +0300 Vladimir Oltean wrote: > Make no mistake, the existing code doesn't disallow reading back the FID > during an ATU Get/Clear Violation operation, and your patch isn't > "allowing" something that wasn't disallowed. > > The documentation for the ATU FID register says that its contents is > ignored before the operation starts, and it contains the returned ATU > entry's FID after the operation completes. > > So the change simply says: don't bother to write the ATU FID register > with zero, it doesn't matter what this contains. This is probably true, > but the patch needs to do what's written on the box. > > Please note that this only even matters at all for switches with > mv88e6xxx_num_databases(chip) > 256, where MV88E6352_G1_ATU_FID is a > dedicated register which this patch avoids writing. For other switches, > the FID is embedded within MV88E6XXX_G1_ATU_CTL or MV88E6XXX_G1_ATU_OP. > So _practically_, for those switches, you are still emitting the > GET_CLR_VIOLATION ATU op with a FID of 0 whether you like it or not, and > this patch introduces a (most likely irrelevant) discrepancy between the > access methods for various switches. > > Please note that this observation is relevant for your future changes to > read back the FID too. As I said here: > https://patchwork.kernel.org/project/netdevbpf/patch/20220524152144.40527-4-schultz.hans+netdev@gmail.com/#24912482 > you can't just assume that the FID lies within the MV88E6352_G1_ATU_FID > register, just look at the way it is packed within mv88e6xxx_g1_atu_op(). > You'll need to unpack it in the same way. I reckon it'll be useful to render some of this info into the commit message and adjust the subject so marking Changes Requested.