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pr=C Message-ID: <49447cee-a0b5-49f9-a10e-1d9afa61dafd@amd.com> Date: Thu, 27 Feb 2025 12:29:29 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] PCI: drop pci_segments_init() To: Jan Beulich CC: Julien Grall , Stefano Stabellini , Volodymyr Babchuk , Bertrand Marquis , Michal Orzel , Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Anthony Perard , "xen-devel@lists.xenproject.org" References: <4ada4343-c65b-456d-b0c2-9ae59937aaff@suse.com> <68fe94fa-21ab-45a9-8664-d8c2638635dc@suse.com> Content-Language: en-US From: Stewart Hildebrand In-Reply-To: <68fe94fa-21ab-45a9-8664-d8c2638635dc@suse.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: None (SATLEXMB04.amd.com: stewart.hildebrand@amd.com does not designate permitted sender hosts) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS2PEPF00003444:EE_|BL3PR12MB6451:EE_ X-MS-Office365-Filtering-Correlation-Id: a7aa9b1b-bb37-401e-b57e-08dd57545e2b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|82310400026|1800799024|36860700013|7053199007; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Feb 2025 17:30:02.4489 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a7aa9b1b-bb37-401e-b57e-08dd57545e2b 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: DS2PEPF00003444.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL3PR12MB6451 On 2/27/25 01:58, Jan Beulich wrote: > On 26.02.2025 20:57, Stewart Hildebrand wrote: >> On 2/26/25 06:38, Jan Beulich wrote: >>> Have callers invoke pci_add_segment() directly instead: With radix tree >>> initialization moved out of the function, its name isn't quite >>> describing anymore what it actually does. >>> >>> On x86 move the logic into __start_xen() itself, to reduce the risk of >>> re-introducing ordering issues like the one which was addressed by >>> 26fe09e34566 ("radix-tree: introduce RADIX_TREE{,_INIT}()"). >>> >>> Signed-off-by: Jan Beulich >>> --- >>> This is entirely optional and up for discussion. There certainly also is >>> an argument towards keeping the function. Otoh on Arm there is the still >>> open question whether segment 0 really is kind of special there (as it >>> is on x86, largely for historical reasons), or whether the code can be >>> dropped there altogether. >> >> Segment 0 is not special on Arm as far as I'm aware. You can have a >> perfectly functioning system with only, say, segment 1, for example: >> >> (XEN) ==== PCI devices ==== >> (XEN) ==== segment 0001 ==== >> (XEN) 0001:00:01.0 - d0 - node -1 >> (XEN) 0001:00:00.0 - d0 - node -1 >> >> Segment numbers can be arbitrarily chosen by specifying the >> linux,pci-domain device tree property. > > Right, that was the vague understanding I had. > >>> --- a/xen/arch/arm/pci/pci.c >>> +++ b/xen/arch/arm/pci/pci.c >>> @@ -88,7 +88,8 @@ static int __init pci_init(void) >>> if ( !pci_passthrough_enabled ) >>> return 0; >>> >>> - pci_segments_init(); >>> + if ( pci_add_segment(0) ) >>> + panic("Could not initialize PCI segment 0\n"); >> >> IMO it's okay to remove the call here since there is already a call to >> pci_add_segment() in >> xen/arch/arm/pci/pci-host-common.c:pci_host_common_probe() > > Is there? I can't see one, so maybe you're working from a tree with extra > patches applied? Ah, you're right, sorry, I was looking at a downstream tree. The associated segment would be added in Xen upon the first time Dom0 calls PHYSDEVOP_pci_device_add.