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Miller" , "Eric Dumazet" , Jakub Kicinski , "Paolo Abeni" , , Subject: Re: [PATCH net-next 10/14] mlxsw: pci: Remove obsolete 32-bit DMA mask fallback In-Reply-To: <20260903084339.870562-11-zhouruizhe@resnics.com> (Ruizhe Zhou's message of "Thu, 3 Sep 2026 16:43:35 +0800") References: <20260903084339.870562-1-zhouruizhe@resnics.com> <20260903084339.870562-11-zhouruizhe@resnics.com> User-Agent: mu4e 1.12.15; emacs 30.2 Date: Fri, 4 Sep 2026 18:00:24 +0200 Message-ID: <8733vpypk7.fsf@pmachata.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-ClientProxiedBy: rnnvmail201.nvidia.com (10.129.68.8) To rnnvmail201.nvidia.com (10.129.68.8) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF000037A4:EE_|DM4PR12MB7527:EE_ X-MS-Office365-Filtering-Correlation-Id: 505779f3-0f7a-474d-dab4-08df0a9dbab7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|82310400026|36860700016|376014|1800799024|11063799006|56012099006|10067099003|4143699003|6133799003|18002099003|22082099003|13003099007; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230040)(23010399003)(82310400026)(36860700016)(376014)(1800799024)(11063799006)(56012099006)(10067099003)(4143699003)(6133799003)(18002099003)(22082099003)(13003099007);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 0hGDeRLxLNoSNBSsmGnBdOjqiS2QQ66++NTbpIamUuBEsYYGBzNWrSA1aRJJNL1h7C+kqbQl6wKVatGK9/UsmYQSJ2K7gGnlzTi+shGJzf6JQ+wSL43hO9AGZs+ScM3MuT2AajqSp9iUjasepppNA4sZovdIjy/RQoTq/NYSV+q5EynKU5FH15ZGDQeptMcKhmnXLK3gkuSNppjwInGXa2psx0SXbN/z8hv0L3xp4bGZq7nkstNiD0R0YCQrW1Nc7Le4VR/0jL/LHHwnIezbC4syjAI6qjOHBOGBpu0oB79PT/9Q9K/eJj4vhN65e//PSCU7aQe/V6CfYpDd1DVQBAIu/6nPcuNnZ++OF546PRKKrPVu+IydfTYlBKPWCepxRMax/aVZrfg04u55BBd3U/zTGR+sL+WgOupQoBQSv2n0XIuBSOHTlTxJyU+mVDE4 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Sep 2026 16:01:06.7308 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 505779f3-0f7a-474d-dab4-08df0a9dbab7 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF000037A4.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB7527 Ruizhe Zhou writes: > The DMA API guarantees support for masks of 32 bits or wider and > explicitly identifies retrying a 32-bit mask after a 64-bit request as > incorrect: > https://docs.kernel.org/core-api/dma-api-howto.html#dma-addressing-capabilities > > Remove the obsolete fallback while retaining the error check so that a > genuine DMA setup failure is still reported and aborts initialization. > Update the error message to identify the combined streaming and coherent > DMA mask operation. > > Signed-off-by: Ruizhe Zhou Doco: "dma_set_mask_and_coherent() never return fail when DMA_BIT_MASK(64)." Checking code, the only way that I see that dma_set_mask_and_coherent() returns error is if dma_supported() returns 0. This could happen if: - use_dma_iommu() fails, but that doesn't consider mask, so retrying with 32 doesn't help. - if ops->dma_supported fails. But I checked several architectures where mlxsw could even theoretically be relevant, and it's basically always some mask > X type of expression, so retrying with a smaller mask does not help. - The fallback of dma_direct_supported() is like that as well. So yeah. I think this is correct. Reviewed-by: Petr Machata > --- > drivers/net/ethernet/mellanox/mlxsw/pci.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) > > diff --git a/drivers/net/ethernet/mellanox/mlxsw/pci.c b/drivers/net/ethernet/mellanox/mlxsw/pci.c > index bfe3268dfdc1..dceb69945d26 100644 > --- a/drivers/net/ethernet/mellanox/mlxsw/pci.c > +++ b/drivers/net/ethernet/mellanox/mlxsw/pci.c > @@ -2429,11 +2429,8 @@ static int mlxsw_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id) > > err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64)); > if (err) { > - err = dma_set_mask(&pdev->dev, DMA_BIT_MASK(32)); > - if (err) { > - dev_err(&pdev->dev, "dma_set_mask failed\n"); > - goto err_pci_set_dma_mask; > - } > + dev_err(&pdev->dev, "dma_set_mask_and_coherent failed\n"); > + goto err_pci_set_dma_mask; > } > > if (pci_resource_len(pdev, 0) < MLXSW_PCI_BAR0_SIZE) {