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Thu, 20 Aug 2026 15:33:50 +0000 Date: Thu, 20 Aug 2026 17:33:30 +0200 From: Maciej Fijalkowski To: Stanislav Fomichev CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH net v3 3/3] net: stmmac: document oversized AF_XDP frame handling Message-ID: References: <20260819160535.1472459-1-sdf@fomichev.me> <20260819160535.1472459-4-sdf@fomichev.me> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260819160535.1472459-4-sdf@fomichev.me> X-ClientProxiedBy: TL2P290CA0007.ISRP290.PROD.OUTLOOK.COM (2603:1096:950:2::9) To DM4PR11MB6117.namprd11.prod.outlook.com (2603:10b6:8:b3::19) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6117:EE_|CO1PR11MB4818:EE_ X-MS-Office365-Filtering-Correlation-Id: 5b8d7a9c-448d-46fe-7cbe-08defed06ef5 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|366016|7416014|376014|1800799024|6133799003|18002099003|22082099003|11063799006|4143699003|56012099006|10067099003; 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Instead, leave the > completion pending so the ring eventually wedges and increment the drop > counter to expose the application error without risking hardware > misbehavior. > > Document this intentional ring imbalance at the check. > > Signed-off-by: Stanislav Fomichev > --- > drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > index 62de03e65a90..6a532747c039 100644 > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > @@ -2713,6 +2713,10 @@ static bool stmmac_xdp_xmit_zc(struct stmmac_priv *priv, u32 queue, u32 budget) > if (priv->est && priv->est->enable && > priv->est->max_sdu[queue] && > xdp_desc.len > priv->est->max_sdu[queue]) { > + /* Completions are ordered, so this descriptor cannot > + * be completed safely. Wedge the ring to expose the > + * application error instead. > + */ > priv->xstats.max_sdu_txq_drop[queue]++; > continue; Hmm. I read the discussion on v2. Maybe we could cancel cq entry here in this branch? Also it feels like something achievable at bind time when taprio is configured and vice versa? Otherwise we over-commit cq entries. > } > -- > 2.53.0-Meta >