linux-kernel - Re: [PATCH 1/2] net: dsa: ksz: pad frame to 64 bytes for transmission

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Message-ID: <20201129165627.GA2234159@lunn.ch>
Date:   Sun, 29 Nov 2020 17:56:27 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Jean Pihet <jean.pihet@...oldbits.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ryan Barnett <ryan.barnett@...kwellcollins.com>,
        Conrad Ratschan <conrad.ratschan@...kwellcollins.com>,
        Hugo Cornelis <hugo.cornelis@...ensium.com>,
        Arnout Vandecappelle <arnout.vandecappelle@...ensium.com>
Subject: Re: [PATCH 1/2] net: dsa: ksz: pad frame to 64 bytes for transmission

On Sun, Nov 29, 2020 at 11:23:59AM +0100, Jean Pihet wrote:
> Some ethernet controllers (e.g. TI CPSW) pad the frames to a minimum
> of 64 bytes before the FCS is appended. This causes an issue with the
> KSZ tail tag which could not be the last byte before the FCS.
> Solve this by padding the frame to 64 bytes minus the tail tag size,
> before the tail tag is added and the frame is passed for transmission.

Hi Jean

what tree is this based on? Have you seen

commit 88fda8eefd9a7a7175bf4dad1d02cc0840581111
Author: Christian Eggers <ceggers@...i.de>
Date:   Sun Nov 1 21:16:10 2020 +0200

    net: dsa: tag_ksz: don't allocate additional memory for padding/tagging
    
    The caller (dsa_slave_xmit) guarantees that the frame length is at least
    ETH_ZLEN and that enough memory for tail tagging is available.