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[175.34.62.5]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3434c344838sm6476363a91.15.2025.11.08.16.49.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 08 Nov 2025 16:49:46 -0800 (PST) Message-ID: Date: Sun, 9 Nov 2025 10:49:32 +1000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 15/33] arm_mpam: Add helpers for managing the locking around the mon_sel registers To: Ben Horgan , james.morse@arm.com Cc: amitsinght@marvell.com, baisheng.gao@unisoc.com, baolin.wang@linux.alibaba.com, bobo.shaobowang@huawei.com, carl@os.amperecomputing.com, catalin.marinas@arm.com, dakr@kernel.org, dave.martin@arm.com, david@redhat.com, dfustini@baylibre.com, fenghuay@nvidia.com, gregkh@linuxfoundation.org, guohanjun@huawei.com, jeremy.linton@arm.com, jonathan.cameron@huawei.com, kobak@nvidia.com, lcherian@marvell.com, lenb@kernel.org, linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, lpieralisi@kernel.org, peternewman@google.com, quic_jiles@quicinc.com, rafael@kernel.org, robh@kernel.org, rohit.mathew@arm.com, scott@os.amperecomputing.com, sdonthineni@nvidia.com, sudeep.holla@arm.com, tan.shaopeng@fujitsu.com, will@kernel.org, xhao@linux.alibaba.com, Shaopeng Tan References: <20251107123450.664001-1-ben.horgan@arm.com> <20251107123450.664001-16-ben.horgan@arm.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20251107123450.664001-16-ben.horgan@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/7/25 10:34 PM, Ben Horgan wrote: > From: James Morse > > The MSC MON_SEL register needs to be accessed from hardirq for the overflow > interrupt, and when taking an IPI to access these registers on platforms > where MSC are not accessible from every CPU. This makes an irqsave > spinlock the obvious lock to protect these registers. On systems with SCMI > or PCC mailboxes it must be able to sleep, meaning a mutex must be used. > The SCMI or PCC platforms can't support an overflow interrupt, and > can't access the registers from hardirq context. > > Clearly these two can't exist for one MSC at the same time. > > Add helpers for the MON_SEL locking. For now, use a irqsave spinlock and > only support 'real' MMIO platforms. > > In the future this lock will be split in two allowing SCMI/PCC platforms > to take a mutex. Because there are contexts where the SCMI/PCC platforms > can't make an access, mpam_mon_sel_lock() needs to be able to fail. Do > this now, so that all the error handling on these paths is present. This > allows the relevant paths to fail if they are needed on a platform where > this isn't possible, instead of having to make explicit checks of the > interface type. > > Tested-by: Fenghua Yu > Reviewed-by: Jonathan Cameron > Tested-by: Shaopeng Tan > Tested-by: Peter Newman > Signed-off-by: James Morse > Signed-off-by: Ben Horgan > --- > Changes since v3: > use devm_mutex_init() > include tiying > stray comma (Jonathan) > --- > drivers/resctrl/mpam_devices.c | 2 ++ > drivers/resctrl/mpam_internal.h | 39 +++++++++++++++++++++++++++++++++ > 2 files changed, 41 insertions(+) > Reviewed-by: Gavin Shan