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Tue, 19 May 2026 18:04:19 -0700 Date: Tue, 19 May 2026 18:04:18 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: Bjorn Helgaas , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v4 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices Message-ID: References: <20260519222335.GK3602937@nvidia.com> <20260519234801.GA21369@bhelgaas> <20260520000504.GQ3602937@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260520000504.GQ3602937@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1PEPF00012E84:EE_|BL1PR12MB5756:EE_ X-MS-Office365-Filtering-Correlation-Id: 1a5ed148-2ea5-47f0-bc09-08deb60bc2bc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700016|1800799024|7416014|376014|4143699003|11063799006|22082099003|18002099003|56012099003|5023799004; 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)(82310400026)(36860700016)(1800799024)(7416014)(376014)(4143699003)(11063799006)(22082099003)(18002099003)(56012099003)(5023799004);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: vij1HBOPxXLJD6dVsGfr3QghMd4Qpu45o0EtcHW1a9yRGp9+Wy+1c2Gq3W6FRaO7vStWc4VMbWIYtaVdq7EA3Cn7X2oEN6LI2Uc6mJdmeG/wYtWEjUFz/M+Nfhsg40luqT56ulqbCBooHdl//SfWb19CQtsfeM0cs/eEy4eWdxvbn2kikVzhg+JFd6aZzGHDvvtirPN73OwVf2aWE1bAlf+qB7JVUDsYPwu/0WSoUufNrcryOwakYfB2JUIxtOXPPTqf8wFowG++/n2mcO9eQ5BHuNj5aLKHIv1nms06cnBeB/LR6tN/6znahqAKNbrFVBNQnl+04lvApBcvJD797d6kLkUdyNh987LQNWlKfL/WbgXJyaNQ38KxCC27pqSWKMKEkpiwVb8v1frxTlsZ988PUPoEdKiLIEm0Gek0byBpFMxWv4RoGBTQYhXlcJFj X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 May 2026 01:04:36.0257 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 1a5ed148-2ea5-47f0-bc09-08deb60bc2bc 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: CO1PEPF00012E84.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5756 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260519_180445_640910_264B39B9 X-CRM114-Status: GOOD ( 26.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, May 19, 2026 at 09:05:04PM -0300, Jason Gunthorpe wrote: > On Tue, May 19, 2026 at 06:48:01PM -0500, Bjorn Helgaas wrote: > > On Tue, May 19, 2026 at 07:23:35PM -0300, Jason Gunthorpe wrote: > > > On Tue, May 19, 2026 at 02:36:49PM -0500, Bjorn Helgaas wrote: > > > > One motivation for putting this in the PCI core was to use the quirk > > > > infrastructure, but this series doesn't use any of that. It doesn't > > > > declare any fixups, e.g., DECLARE_PCI_FIXUP_FINAL, and it doesn't > > > > update any state cached by the PCI core. > > > > > > It works like the acs quirks that are in the quirks file, which are > > > also arguably only used by iommu too :) > > > > True, although ACS has a lot more PCI-specific grunge in it, including > > all the "pci=config_acs" and "pci=disable_acs_redir" stuff. > > > > > I'm not keen on spreading lists of device ids for PCI quirks to iommu > > > files, but it would be OK to move pci_ats_always_on() to > > > iommu_ats_always_on() that calls the PCI quirk function. > > > > Yeah, I guess it's fair to collect the device IDs in PCI since this is > > about characteristics of the device. > > > > If we leave stuff in drivers/pci/, I would prefer that part of it be > > named to be purely informational, i.e., "CXL.cache_enabled" or > > something similar that would also cover the NVIDIA devices. > > Yeah, that's fair, so let's rename it to > > pci_translated_required() > > ie the device requires translated requests to function. This is what > CXL.cache implies (IIRC I was told the spec specifically says this) > > Requiring translated requests implies you have to enable ATS in the > system. Perhaps we could let IOMMU drivers check: pci_cxl_is_cache_capable() || pci_dev_specific_is_pre_cxl() directly? Thanks Nicolin