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Tue, 6 Dec 2022 23:44:58 +0000 From: To: CC: , , , , , , , , Subject: RE: [PATCH net-next v3 1/2] dsa: lan9303: Add port_max_mtu API Thread-Topic: [PATCH net-next v3 1/2] dsa: lan9303: Add port_max_mtu API Thread-Index: AQHZCaGGUS2s+i6LNUmfdfFZp/Wl6a5hNZMAgABQdTA= Date: Tue, 6 Dec 2022 23:44:58 +0000 Message-ID: References: <20221206183500.6898-1-jerry.ray@microchip.com> <20221206183500.6898-2-jerry.ray@microchip.com> <20221206185616.2ksuvlcmgelsfvw5@skbuf> In-Reply-To: <20221206185616.2ksuvlcmgelsfvw5@skbuf> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=microchip.com; x-ms-publictraffictype: Email x-ms-traffictypediagnostic: MWHPR11MB1693:EE_|SJ0PR11MB5868:EE_ x-ms-office365-filtering-correlation-id: 62ecb261-8a46-4c4b-ab34-08dad7e3e274 x-ms-exchange-senderadcheck: 1 x-ms-exchange-antispam-relay: 0 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 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 x-forefront-antispam-report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:MWHPR11MB1693.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(346002)(376002)(136003)(396003)(366004)(39860400002)(451199015)(55016003)(33656002)(478600001)(38070700005)(7416002)(38100700002)(6506007)(7696005)(71200400001)(122000001)(2906002)(83380400001)(8676002)(26005)(41300700001)(9686003)(52536014)(186003)(8936002)(54906003)(6916009)(316002)(66946007)(64756008)(66476007)(76116006)(86362001)(5660300002)(4326008)(66446008)(66556008);DIR:OUT;SFP:1101; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: MWHPR11MB1693.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 62ecb261-8a46-4c4b-ab34-08dad7e3e274 X-MS-Exchange-CrossTenant-originalarrivaltime: 06 Dec 2022 23:44:58.2878 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 3f4057f3-b418-4d4e-ba84-d55b4e897d88 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: TAHeiVlk4oOgSAs/Rx7UJ0F9oAPOW9p5xfsNao9kEMWAyG20HUqNHX7VV4d6qF5ors9+1eOOxkSYBK+1Alp/rA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR11MB5868 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > +/* For non-cpu ports, the max frame size is 1518. > > + * The CPU port supports a max frame size of 1522. > > + * There is a JUMBO flag to make the max size 2048, but this driver > > + * presently does not support using it. > > + */ > > +static int lan9303_port_max_mtu(struct dsa_switch *ds, int port) > > +{ > > + struct net_device *p =3D dsa_port_to_master(dsa_to_port(ds, port)= ); >=20 > You can put debugging prints in the code, but please, in the code that > you submit, do remove gratuitous poking in the master net_device. >=20 > > + struct lan9303 *chip =3D ds->priv; > > + > > + dev_dbg(chip->dev, "%s(%d) entered. NET max_mtu is %d", > > + __func__, port, p->max_mtu); > > + > > + if (dsa_port_is_cpu(dsa_to_port(ds, port))) >=20 > The ds->ops->port_max_mtu() function is never called for the CPU port. > You must know this, you put a debugging print right above. If this would > have been called for anything other than user ports, dsa_port_to_master() > would have triggered a NULL pointer dereference (dp->cpu_dp is set to > NULL for CPU ports). >=20 > So please remove dead code. >=20 I've written the function to handle being called with any port. While I couldn't directly exercise calling the port_max_mtu with the cpu port, I di= d simulate it to verify it would work. I'm using the dsa_to_port() rather than the dsa_port_to_master() function. I'd rather include support for calling the api with the cpu port. I didn't want to assume otherwise. That's why I don't consider this dead code. > > + return 1522 - ETH_HLEN - ETH_FCS_LEN; > > + else > > + return 1518 - ETH_HLEN - ETH_FCS_LEN; >=20 > Please replace "1518 - ETH_HLEN - ETH_FCS_LEN" with "ETH_DATA_LEN". >=20 > Which brings me to a more serious question. If you say that the max_mtu > is equal to the default interface MTU (1500), and you provide no means > for the user to change the MTU to a different value, then why write the > patch? What behaves differently with and without it? >=20 I began adding the port_max_mtu api to attempt to get rid of the following error message: "macb f802c000.ethernet eth0: error -22 setting MTU to 1504 to include DSA = overhead" If someone were to check the max_mtu supported on the CPU port of the LAN93= 03, they would see that 1504 is okay. > > +} > > + > > static const struct dsa_switch_ops lan9303_switch_ops =3D { > > .get_tag_protocol =3D lan9303_get_tag_protocol, > > .setup =3D lan9303_setup, > > @@ -1299,6 +1318,7 @@ static const struct dsa_switch_ops lan9303_switch= _ops =3D { > > .port_fdb_dump =3D lan9303_port_fdb_dump, > > .port_mdb_add =3D lan9303_port_mdb_add, > > .port_mdb_del =3D lan9303_port_mdb_del, > > + .port_max_mtu =3D lan9303_port_max_mtu, > > }; >=20 Regards, Jerry.