From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from CH4PR04CU002.outbound.protection.outlook.com (mail-northcentralusazon11013058.outbound.protection.outlook.com [40.107.201.58]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 39F6081ACA; Thu, 30 Apr 2026 23:28:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.201.58 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777591735; cv=fail; b=SU/ntVzSKYU2006Ij+kzh1Bc87MtkKqBva3/s/fXY5+xsUFL2ijXudTGKkPRqP1BaFapzNtcwx95tcjK0W83wTI0u4lFpHMSlSQnvhJdDLboTzYnnO7WtfdMy6xcU1MOF9spndyyJSorwoKq/jpNa2SMpTLbhpNmWbx59zIh8+Y= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777591735; c=relaxed/simple; bh=6b9Vd6TlijgcvXMNJ8qFtyei7G88cZrT4mbPgr3T/SU=; h=Date:From:To:CC:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PEFkSY+hni7Nh1RSfOj6Qs2E/bd5+fjR0VYnlcKhMdEgUBDYlas5+Hj/hoM2HOXu765UNv7CaJOmzSZJ6kZomJtflD4vWzMP5tu36AelZv4i4yKXu7jgyehzRUw+UhRr++DilZKahpCPbKjNYgtvZcEOFc7n89DdlNDMMMLyPuM= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=mMLBm6kV; arc=fail smtp.client-ip=40.107.201.58 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="mMLBm6kV" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=IRUBYmhAuYfAijpbVwQQ6MbIu/KB1LGUpheZWgJwUvzR0y0XF0IJMzOo+d2CfeCNOEcgi4eCHrqKv1DRwveKSSQ22X2Iia5GQcw/dFy+VL5wGVfiGB6owb8a3fqvxmIdOyvSHrxRdQMaCdmzLWj360QBs4szUiP8pylJFIXWO8anTE4nbGn/IJ5AmSd3j35Hk69ubIhyV0w3ADKyAWGyny7Asq+8NeBvAowCQcp4trrpfJbD6zAzlk/xtETLlWUKGdfDun0JR53REdOrQamzXCtPXL9UmbH2Z2D5GOCh+MxYMleIMI6nSY7zuITQTQ28z8KrsebbHBV0zMIE9fIx4w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=f5eETolv2CRJ+KGuzqHXNWHz75SkAhmrcTAnZvVauEE=; b=DcEBcN4HBFB8NWFbLvBWERyOGFPSntjOFSqRbi0GMnmezSqbxkTA+ehmkCGBQrPRj1c3HtOcoFPwBaDuK0DCHoJA89sEoEO0sOGlA5J6nojLKvgDKaCVi6ymK5+NXw8KGoifvj+7Y+KERpXkiMybXtfyR9apmccjBlXK8P23Ijx8uoHAivTItFD6Z6wqiNu3RzkDO61xi48aTpolc6IjsJcwNTuHsVSvQP4Z87obrTjMOrZbUd0DmOi8gRNvfnMjD0qRso+vi1OGvi7KTWaWDJeTLgYZxJ/BW6i1mi6+/5HXco0To9G6e3y2AsdHFzdp+wHB2tp0cfkvI2346cY4mA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass (sender ip is 216.228.117.161) smtp.rcpttodomain=kernel.org smtp.mailfrom=nvidia.com; dmarc=pass (p=reject sp=reject pct=100) action=none header.from=nvidia.com; dkim=none (message not signed); arc=none (0) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=f5eETolv2CRJ+KGuzqHXNWHz75SkAhmrcTAnZvVauEE=; b=mMLBm6kV3YOXYYJRO8e/70BpjU0vtzzslFfTmDnSUjzo0eu4teU98t91S7Zuhi2jYjJZ75CdkSXrA+ebqHf4wcc/bHafQBH905u8wKDSpG4veX7yExnCUY5Xz2/XnjyNmSYrWYXVWjKJZx3nbcH9jW7iZQPltdEg9LlmQrjMx4YKhfjIWxEWHjWvbLNxCx669JFcue4suZSgwJrExaE7p8LKG2zAyTDgbuVz0xa+OlWpUHaO6xWUkd4UFcXtSjJlhe13oLDjXL8FSEAHMZsKnAH1uzL/E3gnFg1OxHL0/v+iHN5KUv8aLQ2OfVcK21bISyOcGu2B7xNOm9BKs3al2g== Received: from BL0PR05CA0003.namprd05.prod.outlook.com (2603:10b6:208:91::13) by CYYPR12MB8890.namprd12.prod.outlook.com (2603:10b6:930:c7::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9870.15; Thu, 30 Apr 2026 23:28:41 +0000 Received: from BL6PEPF0001AB4B.namprd04.prod.outlook.com (2603:10b6:208:91:cafe::e1) by BL0PR05CA0003.outlook.office365.com (2603:10b6:208:91::13) with Microsoft SMTP Server (version=TLS1_3, cipher=TLS_AES_256_GCM_SHA384) id 15.20.9870.16 via Frontend Transport; Thu, 30 Apr 2026 23:28:40 +0000 X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 216.228.117.161) smtp.mailfrom=nvidia.com; dkim=none (message not signed) header.d=none;dmarc=pass action=none header.from=nvidia.com; Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates 216.228.117.161 as permitted sender) receiver=protection.outlook.com; client-ip=216.228.117.161; helo=mail.nvidia.com; pr=C Received: from mail.nvidia.com (216.228.117.161) by BL6PEPF0001AB4B.mail.protection.outlook.com (10.167.242.69) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9870.22 via Frontend Transport; Thu, 30 Apr 2026 23:28:40 +0000 Received: from rnnvmail204.nvidia.com (10.129.68.6) by mail.nvidia.com (10.129.200.67) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.20; Thu, 30 Apr 2026 16:28:20 -0700 Received: from rnnvmail204.nvidia.com (10.129.68.6) by rnnvmail204.nvidia.com (10.129.68.6) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.20; Thu, 30 Apr 2026 16:28:19 -0700 Received: from Asurada-Nvidia (10.127.8.12) by mail.nvidia.com (10.129.68.6) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.20 via Frontend Transport; Thu, 30 Apr 2026 16:28:18 -0700 Date: Thu, 30 Apr 2026 16:28:17 -0700 From: Nicolin Chen To: "Dan Williams (nvidia)" CC: , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v4 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices Message-ID: References: <69f3cc82926_3291a910039@djbw-dev.notmuch> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <69f3cc82926_3291a910039@djbw-dev.notmuch> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL6PEPF0001AB4B:EE_|CYYPR12MB8890:EE_ X-MS-Office365-Filtering-Correlation-Id: 23c0172c-c533-40ce-6828-08dea710366b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|82310400026|36860700016|22082099003|18002099003|56012099003; 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)(1800799024)(7416014)(376014)(82310400026)(36860700016)(22082099003)(18002099003)(56012099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 5QRvdu2tsMZaZN6LaVF5mfJKTnQpODLoriiYBkjWTsLktvO7JrdjeDySsyOcq+ZSbIbea/2/wMMiUp3qI/TmGNNtk0phWymDrrdWo4AJpPyKM5Mi1oZRe16vqbQ1AIOzxtEfhN+IOcZAwsqQ5M9Ka6FjB5Ddy+i7rreix7amE3EoJQywtaWvJGx5ZoGzAdgmpDcMZBAaRHGfpFPFAA0Aag5WcwpfPpElHrg6+viV9PBu7bskH2EXw3+rOuwHFDQ+p7so24CPzX2Jc8bGmEtGw/dFSMtvw3dX/jos/Ra2Ad4ncIv5ILL8egmbbzTOh/e367j/Bj500kSv7oSlgcRlcIcHTZVtwNBDBM82yNmqjrekRkbYDYO1mcOtL9tzY5HKdNU0z7ti4PE0fcjbuapGKbdA6cagOm54xxrC0Q4opB8n7e2kdOpNIl4pPvil7MNL X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Apr 2026 23:28:40.5541 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 23c0172c-c533-40ce-6828-08dea710366b 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: BL6PEPF0001AB4B.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CYYPR12MB8890 On Thu, Apr 30, 2026 at 02:41:22PM -0700, Dan Williams (nvidia) wrote: > > +static bool pci_cxl_ats_always_on(struct pci_dev *pdev) > > +{ > > + int offset; > > + u16 cap; > > + > > + offset = pci_find_dvsec_capability(pdev, PCI_VENDOR_ID_CXL, > > + PCI_DVSEC_CXL_DEVICE); > > + if (!offset) > > + return false; > > + > > + if (pci_read_config_word(pdev, offset + PCI_DVSEC_CXL_CAP, &cap)) > > + return false; > > + > > + return cap & PCI_DVSEC_CXL_CACHE_CAPABLE; [...] > Apologies for coming to this late and forgive me if the following has > already been asked and answered. Why not check for actual CXL.cache > protocol on the wire being present? Actually it would make the patch smaller. The thing is that this is_cxl property wasn't added when I started the series. So, it's not using it. :) > @@ -1733,9 +1733,8 @@ static void set_pcie_cxl(struct pci_dev *dev) > pci_read_config_word(dev, dvsec + PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS, > &cap); > > - dev->is_cxl = FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS_CACHE, cap) || > - FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS_MEM, cap); > - > + dev->is_cxl_cache = FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS_CACHE, cap); > + dev->is_cxl_mem = FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS_MEM, cap); One caveat is that: Here it checks the cap from: PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS (0xE) via PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS (0x7) On the other hand, mine checks from: PCI_DVSEC_CXL_CAP (0xA) via PCI_DVSEC_CXL_DEVICE (0x0) The spec mentions in 8.2.1.3.1 DVSEC Flex Bus Port Capability: " Note: The Mem_Capable, IO_Capable, and Cache_Capable fields are also present in the DVSEC Flex Bus for the device [which is the legacy name for DVSEC 0x0]. This allows for future scalability where multiple devices, each with potentially different capabilities, may be populated behind a single Port. " Not arguing that set_pcie_cxl() is wrong, but I am not sure if there would be any side effect to rely on the "legacy name" over DVSEC 0x0. Is there any CXL expert who can help confirm? Thanks! Nicolin