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Received: from BYAPR12MB2661.namprd12.prod.outlook.com (2603:10b6:a03:67::13) by SA3PR12MB7784.namprd12.prod.outlook.com (2603:10b6:806:317::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9160.18; Fri, 3 Oct 2025 17:56:52 +0000 Received: from BYAPR12MB2661.namprd12.prod.outlook.com ([fe80::f4fa:1948:9ea6:1ee2]) by BYAPR12MB2661.namprd12.prod.outlook.com ([fe80::f4fa:1948:9ea6:1ee2%5]) with mapi id 15.20.9160.017; Fri, 3 Oct 2025 17:56:51 +0000 Message-ID: <8ef43496-fb11-4007-945e-4bc7166e5c1a@nvidia.com> Date: Fri, 3 Oct 2025 10:56:49 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 10/29] arm_mpam: Add cpuhp callbacks to probe MSC hardware To: James Morse , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org Cc: D Scott Phillips OS , carl@os.amperecomputing.com, lcherian@marvell.com, bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com, baolin.wang@linux.alibaba.com, Jamie Iles , Xin Hao , peternewman@google.com, dfustini@baylibre.com, amitsinght@marvell.com, David Hildenbrand , Dave Martin , Koba Ko , Shanker Donthineni , baisheng.gao@unisoc.com, Jonathan Cameron , Rob Herring , Rohit Mathew , Rafael Wysocki , Len Brown , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Catalin Marinas , Will Deacon , Greg Kroah-Hartman , Danilo Krummrich , Lecopzer Chen References: <20250910204309.20751-1-james.morse@arm.com> <20250910204309.20751-11-james.morse@arm.com> Content-Language: en-US From: Fenghua Yu In-Reply-To: <20250910204309.20751-11-james.morse@arm.com> Content-Type: text/plain; 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Probing the hardware will only > happen before MPAM is enabled, walk all the MSCs and probe those we can > reach that haven't already been probed as each CPU's online call is made. > > This adds the low-level MSC register accessors. > > Once all MSCs reported by the firmware have been probed from a CPU in > their respective cpu-affinity set, the probe-time cpuhp callbacks are > replaced. The replacement callbacks will ultimately need to handle > save/restore of the runtime MSC state across power transitions, but for > now there is nothing to do in them: so do nothing. > > The architecture's context switch code will be enabled by a static-key, > this can be set by mpam_enable(), but must be done from process context, > not a cpuhp callback because both take the cpuhp lock. > Whenever a new MSC has been probed, the mpam_enable() work is scheduled > to test if all the MSCs have been probed. If probing fails, mpam_disable() > is scheduled to unregister the cpuhp callbacks and free memory. > > CC: Lecopzer Chen > Signed-off-by: James Morse Reviewed-by: Fenghua Yu Thanks. -Fenghua