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From:   Vladimir Oltean <vladimir.oltean@nxp.com>
To:     Michael Walle <michael@walle.cc>
CC:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        Florian Fainelli <f.fainelli@gmail.com>,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Xiaoliang Yang <xiaoliang.yang_1@nxp.com>
Subject: Re: [PATCH net] net: dsa: felix: re-enable TAS guard band mode
Thread-Topic: [PATCH net] net: dsa: felix: re-enable TAS guard band mode
Thread-Index: AQHXRYykSypWYLAzI0SAeT86R5BMnKrco1+A
Date:   Mon, 10 May 2021 12:23:10 +0000
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References: <20210510110708.11504-1-michael@walle.cc>
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On Mon, May 10, 2021 at 01:07:08PM +0200, Michael Walle wrote:
> Commit 316bcffe4479 ("net: dsa: felix: disable always guard band bit for
> TAS config") disabled the guard band and broke 802.3Qbv compliance.
>=20
> There are two issues here:
>  (1) Without the guard band the end of the scheduling window could be
>      overrun by a frame in transit.
>  (2) Frames that don't fit into a configured window will still be sent.
>=20
> The reason for both issues is that the switch will schedule the _start_
> of a frame transmission inside the predefined window without taking the
> length of the frame into account. Thus, we'll need the guard band which
> will close the gate early, so that a complete frame can still be sent.
> Revert the commit and add a note.
>=20
> For a lengthy discussion see [1].
>=20
> [1] https://lore.kernel.org/netdev/c7618025da6723418c56a54fe4683bd7@walle=
.cc/
>=20
> Fixes: 316bcffe4479 ("net: dsa: felix: disable always guard band bit for =
TAS config")
> Signed-off-by: Michael Walle <michael@walle.cc>
> ---

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>=