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Smith" , Subject: Re: [PATCH v2 01/15] xen: Clean up asm-generic/device.h From: Alejandro Vallejo To: Jan Beulich X-Mailer: aerc 0.20.1 References: <20250605194810.2782031-1-agarciav@amd.com> <20250605194810.2782031-2-agarciav@amd.com> <38104467-fb7e-4aa3-9c78-0f9bf23183eb@suse.com> In-Reply-To: <38104467-fb7e-4aa3-9c78-0f9bf23183eb@suse.com> X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB03.amd.com (10.181.40.144) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PEPF0000013C:EE_|CH3PR12MB8849:EE_ X-MS-Office365-Filtering-Correlation-Id: 2877acb6-72f4-4bc0-6511-08dda4e04828 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700013|7416014|376014|1800799024; X-Microsoft-Antispam-Message-Info: =?utf-8?B?QmI5VVB5SEtmTG1iRG93enc4S0lvYlZReHZxcloxVE1kWnBpMHE4TG9sVGw4?= =?utf-8?B?dXZ1d05kd25JNXZDcEZTM1RLQnY1MXVrZktCSmdtL0ljL1VRbTNKc1RXYjFy?= =?utf-8?B?bDdka1lhQ2g3SnhNSUxYbjdJdWU0YTNDWCtGWHFPSGVsdjRNcjVsUERnWWVo?= =?utf-8?B?Mk9lcFRIOUFRRGVWcy9NQ0p0MFpONXRGSXdORFpqNzVJYUNrS3hnSTVhUzVJ?= =?utf-8?B?RmFIWkpJZXlGS0JZWkdGTlYzQ0RldWtYeWJ5V3BEaklGZWdETkU4bENHMFdN?= =?utf-8?B?V29LazFTdlhqYTFTTlVKNzhwMWFGNlN1T2hmcDdQNGN2emMwY3lZdzZvNUhi?= =?utf-8?B?RzZSeVVxcDdXaERlR1lKL3FiUlZwem1sYzBHL2NVV1ZlNlo1aXR2cTYxN0RR?= =?utf-8?B?dWhvbjJSVDVrNXo5cXRkRE9GTEwzZ1BMN1NsN3VnZ3dMYndiSnZlU01IUFMv?= =?utf-8?B?a2RLcUtKUEg5Umc5d3ZnNnZDMXMydEtEVDVVRzFHMXNvZmhWUkxVaVRacE1i?= =?utf-8?B?bmJ6azA1bnk1ckJTblBMdUdpVFdhWVJmWCtiTXpxRjBoSFRYclZXSWVSeHN3?= =?utf-8?B?ZjdRU3EwQ1YwNzBaa1F3cGxyVE9LSzd4b3lSTjVJRFdNb0J6Rk10UnlzN24x?= =?utf-8?B?cmgrNjM2NU5QazRNbm1LbjY2ZmtwUWxqL1lGQm02Lytob2Mya1AvSFZrRndI?= =?utf-8?B?ZmpzeFVXVDYxZlBwc1hxbnpxVFhSeHV0L09yWUJhbU9UWURybHFXYWlNb1l1?= =?utf-8?B?UjZoZEpnK2NpVjRPM1d2aVNENk92aE1wRkJEQWJiUVh2UnNqd1FCbU8xcm1O?= =?utf-8?B?MVQ3STU0eGp4Z0dIdC81amhlVlJ2WURSWHhYMjM3OTFJZUJGTm56ZCt2NU9G?= =?utf-8?B?QzBwcjJnZmR2bWRPN0wyNXZ0bkllTnAyUUZmQ0EwOEpYTzVFcVFTTHNlV2NI?= =?utf-8?B?bFkxcnF2VmxNdVVqalFUS3hQVkZXWjNmckJQZEhxUExacWx2NU94V1UvM2dj?= =?utf-8?B?MmhlNjQwZnhYdWphWEF2K2MvUEM2OHRjOVAwaFVDZ3F2bHUrUVkva0FwbGZJ?= =?utf-8?B?VWVvYW9rZTkvR3FnMmFROHlJN1FQK2l6SFp0aVpCZEhRYnJWN1lmTTIxbzBo?= =?utf-8?B?MGxtejI5YzN3SGtXc1RKL0szRkR3VkRjYTJ4bkZrQTZoY0VxdlBLaWpvdGE1?= =?utf-8?B?VndlVk15S0RCMHgzNlhkUHdXcHNTdHR1K1Z1T1gvQ2VKNklhOFpuRUdzZ3Qx?= =?utf-8?B?R1cyQWF1SXNFWVFudlQ4anE4bEcrR29wVnZocFc5RGJ3MllxWEZwMi9YMkNh?= =?utf-8?B?cktzTEl5VHQrdzQra3lpYURXNzh5Ri91YTY4b3kzV2NnMm9ycWN5dnVhRzE2?= =?utf-8?B?T0k4SjNpQjRySkdDbkJtWmEwcW1TalhrNlNBN005QVV5Z0MzUUJxZkR0M20y?= =?utf-8?B?emU0WFZmSkxIZ3hlajlTK3B4UmpUMFBwS3ZMVEFKamgyTXJYRmMrYWI1bXAw?= =?utf-8?B?VU0yY1J3Q1JUL1NQRWxadzNtUDFlVXM3K1FralZwanhFZUR2K0pqY2h0Qlpz?= =?utf-8?B?Z2NhOEVmNnE1My9Id1g1TEU3SURTTVVZTm5SMmVPbTVjRE82QytIMXNTT1hK?= =?utf-8?B?WUNUQjVYSGl2MEJqREdOeHUrWlNIeWhTTFNhNDNNQktMeHZReEpSWHlkcUxN?= =?utf-8?B?SE43SUJOaTR5UHRrTWZwQlNGb3AvQVRmTVRUL0gzSDNvanFEaHdDcDZFOXNO?= =?utf-8?B?TGkzOW5zOHFQMGNZb2g4eGwwaGkwSS90UWZ0THRwTGJSYjlJREtxQkw0Y2Yx?= =?utf-8?B?SEx3d2QyeGVTQm9DZFB5UWdzNlYxdTV6Z0NwSVlLdFBxQjdJSHZ2Z3V2YVdL?= =?utf-8?B?YWo1NVlvcno3bVRLbnhOMVBremIzbVZrUmxFUTliT213M3RsMkFDdlo4NU5m?= =?utf-8?B?ekJod240TVpHc083eGI0MlRWVUc0UlJ2QkppT2tQak9FckhjZjd3Mm9XbWVT?= =?utf-8?B?V3dOeXFIVmxCZUZlQ1JnSVRGbURnT2VrNEtKUVd6Y3g0cHhhbW1majVlaTlx?= =?utf-8?Q?xJRGZX?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB04.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(82310400026)(36860700013)(7416014)(376014)(1800799024);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Jun 2025 09:55:34.6183 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2877acb6-72f4-4bc0-6511-08dda4e04828 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CH2PEPF0000013C.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB8849 On Fri Jun 6, 2025 at 8:51 AM CEST, Jan Beulich wrote: > On 05.06.2025 21:47, Alejandro Vallejo wrote: >> --- a/xen/include/asm-generic/device.h >> +++ b/xen/include/asm-generic/device.h >> @@ -1,14 +1,20 @@ >> /* SPDX-License-Identifier: GPL-2.0-only */ >> +/* >> + * This header helps DTB-based architectures abstract away where a part= icular >> + * device came from, be it the DTB itself or enumerated on a PCI bus. >> + */ >> #ifndef __ASM_GENERIC_DEVICE_H__ >> #define __ASM_GENERIC_DEVICE_H__ >> =20 >> +#ifndef CONFIG_HAS_DEVICE_TREE >> +#error "Header for exclusive use of DTB-based architectures" >> +#endif >> + >> #include >> =20 >> enum device_type >> { >> -#ifdef CONFIG_HAS_DEVICE_TREE >> DEV_DT, >> -#endif >> DEV_PCI >> }; > > My objection to these changes remains; as a generic header it ought to be= what > that attribute says - generic. > > Jan It is generic for any architecture where platform DTs exist (that is, anyth= ing but x86). As the commit message states, these guards are useless, provide no function= ality and create the fiction that somehow this header is still relevant on an architecture where only PCI is available. And that's just not true. x86 bei= ng the sole architecture without DTs actively overrides it, and relies on devi= ce_t (defined as struct device here) to be a "struct pci_dev" instead in x86/include/asm/device.h, with dev_to_pci() and pci_to_dev() being irreleva= nt because device_t* and struct pci_dev* are identical types in x86. Removing = that override header is not just a matter of performance. All the IOMMU ops are referencing device_t, while the drivers are assuming pci_dev, so all IOMMU code breaks immediately when x86 tries to use this. To be perfectly clear, this patch isn't strictly required to do DT unflatte= ning on x86. But it's a piece of arm tech debt that Xen is better off without. Cheers, Alejandro