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Miller" , Jakub Kicinski , Xiaoliang Yang 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 Message-ID: <20210510122309.bilonsjl7sxontdd@skbuf> References: <20210510110708.11504-1-michael@walle.cc> In-Reply-To: <20210510110708.11504-1-michael@walle.cc> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: walle.cc; dkim=none (message not signed) header.d=none;walle.cc; dmarc=none action=none header.from=nxp.com; x-originating-ip: [86.127.41.210] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: fce1ed3a-6c07-4954-dd2c-08d913ae5fc3 x-ms-traffictypediagnostic: VI1PR04MB5693: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:655; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; 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charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nxp.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: VI1PR04MB5136.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: fce1ed3a-6c07-4954-dd2c-08d913ae5fc3 X-MS-Exchange-CrossTenant-originalarrivaltime: 10 May 2021 12:23:10.0665 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 686ea1d3-bc2b-4c6f-a92c-d99c5c301635 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: sHOGDJKsua8EomFjou06erJMYDyUu4g99ezio86kVBGpY6l7ePOR/oL6/nb/83fnlLPN1khL1WFgR+lpdajraA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR04MB5693 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 > --- Reviewed-by: Vladimir Oltean =