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Fri, 18 Apr 2025 16:23:23 +0000 Date: Fri, 18 Apr 2025 11:23:55 -0500 From: Ira Weiny To: Smita Koralahalli , , CC: Alison Schofield , Vishal Verma , Ira Weiny , Dan Williams , Jonathan Cameron , Yazen Ghannam , Terry Bowman , Smita Koralahalli , Robert Richter Subject: Re: [PATCH] cxl/core/regs.c: Skip Memory Space Enable check for RCD and RCH Ports Message-ID: <68027c9b27e42_1834cf29448@iweiny-mobl.notmuch> References: <20250407192734.70631-1-Smita.KoralahalliChannabasappa@amd.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20250407192734.70631-1-Smita.KoralahalliChannabasappa@amd.com> X-ClientProxiedBy: MW4PR03CA0310.namprd03.prod.outlook.com (2603:10b6:303:dd::15) To SA1PR11MB6733.namprd11.prod.outlook.com (2603:10b6:806:25c::17) Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SA1PR11MB6733:EE_|BN9PR11MB5307:EE_ X-MS-Office365-Filtering-Correlation-Id: 124e95cc-944e-4b0d-07fe-08dd7e9556d7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016|7053199007; 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Retaining this check may incorrectly cause > cxl_pci_probe() to fail on a valid RCD upstream Port. > > While the specification is explicit only for RCD Upstream Ports, this > check is solely for accessing the RCRB, which is always mapped through > memory space. Therefore, its safe to remove the check entirely. In > practice, firmware reliably enables the Memory Space Enable bit for > RCH Downstream Ports and no failures have been observed. > > Removing the check simplifies the code and avoids unnecessary > special-casing, while relying on BIOS/firmware to configure devices > correctly. Moreover, any failures due to inaccessible RCRB regions > will still be caught either in __rcrb_to_component() or while > parsing the component register block. > > The following failure was observed in dmesg when the check was present: > cxl_pci 0000:7f:00.0: No component registers (-6) > > Fixes: d5b1a27143cb ("cxl/acpi: Extract component registers of restricted hosts from RCRB") > Signed-off-by: Smita Koralahalli Reviewed-by: Ira Weiny [snip]