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Tue, 22 Sep 2026 08:52:11 -0700 From: Jamie Nguyen To: Sudeep Holla CC: Jamie Nguyen , Lorenzo Pieralisi , Hanjun Guo , Catalin Marinas , Will Deacon , "Rafael J. Wysocki" , Len Brown , Dat Mach , , , Subject: Re: [PATCH v2 0/3] ACPI: arm64: FFH Operation Region support for FF-A (offset 2) Date: Tue, 22 Sep 2026 08:52:11 -0700 Message-ID: <20260922155211.676134-1-jamien@nvidia.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260922-purring-fennec-of-exercise-bbce5e@sudeepholla> References: <20260901192906.133670-1-jamien@nvidia.com> <20260922-purring-fennec-of-exercise-bbce5e@sudeepholla> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN3PEPF00022BDA:EE_|IA0PR12MB7577:EE_ X-MS-Office365-Filtering-Correlation-Id: 2f367d70-681b-4fa2-1632-08df18c1891f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|23010399003|7416014|1800799024|36860700016|82310400026|6133799003|10067099003|11063799006|4143699003|56012099006|18002099003|22082099003; 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)(376014)(23010399003)(7416014)(1800799024)(36860700016)(82310400026)(6133799003)(10067099003)(11063799006)(4143699003)(56012099006)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: bN15vzE9wnMIM0GROtawBhJYDUXMCW0pWJ1MK73Y8TulqVFs4Xg98FGaX/CMvECDjrivW1HrFTSIhTjytffWCUcAyxDoDU9SsdBPW/1fD/3lVCI+K8gljL0Uqfmo/3mCJxAYwa7w44IRlTj3J85e4r2FBtWpee7oQT7fiYC9JCCDgCOE8ZRiVAmJnLM0cI6MO+5DxSg8d5pC6vLVzF7ZU3dwLjUnfm7OEjeNLlN5xIS8WLFwHAl1xXZRDNuojE6yQmfrAguEHZKRDg30WaPsiSFjhIXKlTFQ12JrVWHtD+0UNa8F9XvAYPXWoIgATilIEUmMKpgo8IcyS+f6mL2Asu570cgIRkIz3xrQqspPkMR1UZv+y2rt0ACx2mwBrH6Qv+V6pdlBOQ3osufGlY4M1Ja8Q+S7UpdKa1XpdAKiT7AvFQKg9SEm8U2olDGRgCe9 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Sep 2026 15:52:41.6284 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2f367d70-681b-4fa2-1632-08df18c1891f 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: BN3PEPF00022BDA.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR12MB7577 On Tue, Sep 22, 2026 at 09:46:59AM +0100, Sudeep Holla wrote: > Could you clarify how the build and runtime behavior are protected when > the FF-A driver is disabled? There is no build-time dependency from ACPI FFH to the FF-A driver. The registration direction is from FF-A into FFH: the FF-A driver registers an optional backend after probe and unregisters it on removal. With CONFIG_ARM_FFA_TRANSPORT=n, no backend is registered and an offset 2 access returns FFH_FFA_NOT_SUPPORTED. With CONFIG_ACPI_FFH=n, the registration functions are static inline stubs. I have also built CONFIG_ACPI_FFH=y with CONFIG_ARM_FFA_TRANSPORT=n. The W=1 build and full vmlinux link are clean, with no unresolved references to the FF-A transport driver. I'll mention this case in the v3 cover letter. > Are there any other technical justifications for this tight coupling? FFA_MSG_SEND_DIRECT_REQ2 requires FF-A state already owned by the driver: the selected SMC or HVC conduit, the sender endpoint ID from FFA_ID_GET, UUID-to-endpoint resolution through the partition discovery ABIs, REQ2 feature detection, and FFA_RUN handling after FFA_YIELD or FFA_INTERRUPT. Open-coding those operations in ffh.c would duplicate FF-A initialization and state management. The ops registration lets FFH use that state when the driver is available while degrading cleanly when it is not.