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[2003:ea:8f38:4600:6dfe:cdb3:c4f9:2744]) by smtp.googlemail.com with ESMTPSA id w7sm110919wro.43.2021.04.08.11.22.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Apr 2021 11:22:39 -0700 (PDT) Subject: Re: [PATCH net v1] Revert "lan743x: trim all 4 bytes of the FCS; not just 2" To: George McCollister , Sven Van Asbroeck Cc: Bryan Whitehead , David S Miller , Jakub Kicinski , Microchip Linux Driver Support , netdev , open list References: <20210408172353.21143-1-TheSven73@gmail.com> From: Heiner Kallweit Message-ID: <820ed30b-90f4-2cba-7197-6c6136d2e04e@gmail.com> Date: Thu, 8 Apr 2021 20:22:34 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08.04.2021 20:00, George McCollister wrote: > On Thu, Apr 8, 2021 at 12:46 PM Sven Van Asbroeck wrote: >> >> Hi George, >> >> On Thu, Apr 8, 2021 at 1:36 PM George McCollister >> wrote: >>> >>> Can you explain the difference in behavior with what I was observing >>> on the LAN7431? >> >> I'm not using DSA in my application, so I cannot test or replicate >> what you were observing. It would be great if we could work together >> and settle on a solution that is acceptable to both of us. > > Sounds good. > >> >>> I'll retest but if this is reverted I'm going to start >>> seeing 2 extra bytes on the end of frames and it's going to break DSA >>> with the LAN7431 again. >>> >> >> Seen from my point of view, your patch is a regression. But perhaps my >> patch set is a regression for you? Catch 22... >> >> Would you be able to identify which patch broke your DSA behaviour? >> Was it one of mine? Perhaps we can start from there. > > Yes, first I'm going to confirm that what is in the net branch still > works (unlikely but perhaps something else could have broken it since > last I tried it). > Then I'll confirm the patch which I believe broke it actually did and > report back. > >> >> Sven Just an idea: RX_HEAD_PADDING is an alias for NET_IP_ALIGN that can have two values: 0 and 2 The two systems you use may have different NET_IP_ALIGN values. This could explain the behavior. Then what I proposed should work for both of you: frame_length - ETH_FCS_LEN