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>,
Claudiu Manoil <claudiu.manoil@nxp.com>,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
"UNGLinuxDriver@microchip.com" <UNGLinuxDriver@microchip.com>,
Andrew Lunn <andrew@lunn.ch>,
Vivien Didelot <vivien.didelot@gmail.com>,
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
Date: Mon, 10 May 2021 12:23:10 +0000 [thread overview]
Message-ID: <20210510122309.bilonsjl7sxontdd@skbuf> (raw)
In-Reply-To: <20210510110708.11504-1-michael@walle.cc>
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.
>
> 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.
>
> 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.
>
> For a lengthy discussion see [1].
>
> [1] https://lore.kernel.org/netdev/c7618025da6723418c56a54fe4683bd7@walle.cc/
>
> 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>
next prev parent reply other threads:[~2021-05-10 12:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-10 11:07 [PATCH net] net: dsa: felix: re-enable TAS guard band mode Michael Walle
2021-05-10 12:23 ` Vladimir Oltean [this message]
2021-05-10 21:50 ` patchwork-bot+netdevbpf
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