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Sun, 18 Jan 2026 22:37:59 -0800 (PST) Received: from [10.72.112.128] ([209.132.188.88]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35273277f68sm4098077a91.0.2026.01.18.22.37.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 18 Jan 2026 22:37:59 -0800 (PST) Message-ID: <7c224083-595b-432f-9147-1e8067df634c@redhat.com> Date: Mon, 19 Jan 2026 14:37:46 +0800 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 v3 08/47] arm64: mpam: Advertise the CPUs MPAM limits to the driver To: Ben Horgan Cc: amitsinght@marvell.com, baisheng.gao@unisoc.com, baolin.wang@linux.alibaba.com, carl@os.amperecomputing.com, dave.martin@arm.com, david@kernel.org, dfustini@baylibre.com, fenghuay@nvidia.com, james.morse@arm.com, jonathan.cameron@huawei.com, kobak@nvidia.com, lcherian@marvell.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, peternewman@google.com, punit.agrawal@oss.qualcomm.com, quic_jiles@quicinc.com, reinette.chatre@intel.com, rohit.mathew@arm.com, scott@os.amperecomputing.com, sdonthineni@nvidia.com, tan.shaopeng@fujitsu.com, xhao@linux.alibaba.com, catalin.marinas@arm.com, will@kernel.org, corbet@lwn.net, maz@kernel.org, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, kvmarm@lists.linux.dev References: <20260112165914.4086692-1-ben.horgan@arm.com> <20260112165914.4086692-9-ben.horgan@arm.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20260112165914.4086692-9-ben.horgan@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Ben, On 1/13/26 12:58 AM, Ben Horgan wrote: > From: James Morse > > Requestors need to populate the MPAM fields for any traffic they send on > the interconnect. For the CPUs these values are taken from the > corresponding MPAMy_ELx register. Each requestor may have a limit on the > largest PARTID or PMG value that can be used. The MPAM driver has to > determine the system-wide minimum supported PARTID and PMG values. > > To do this, the driver needs to be told what each requestor's limit is. > > CPUs are special, but this infrastructure is also needed for the SMMU and > GIC ITS. Call the helper to tell the MPAM driver what the CPUs can do. > > The return value can be ignored by the arch code as it runs well before the > MPAM driver starts probing. > > Reviewed-by: Jonathan Cameron > Signed-off-by: James Morse > Signed-off-by: Ben Horgan > --- > arch/arm64/kernel/mpam.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/arch/arm64/kernel/mpam.c b/arch/arm64/kernel/mpam.c > index 9866d2ca0faa..e6feff2324ac 100644 > --- a/arch/arm64/kernel/mpam.c > +++ b/arch/arm64/kernel/mpam.c > @@ -3,6 +3,7 @@ > > #include > > +#include > #include > #include > > @@ -11,3 +12,14 @@ DEFINE_PER_CPU(u64, arm64_mpam_default); > DEFINE_PER_CPU(u64, arm64_mpam_current); > > u64 arm64_mpam_global_default; > + > +static int __init arm64_mpam_register_cpus(void) > +{ > + u64 mpamidr = read_sanitised_ftr_reg(SYS_MPAMIDR_EL1); > + u16 partid_max = FIELD_GET(MPAMIDR_EL1_PARTID_MAX, mpamidr); > + u8 pmg_max = FIELD_GET(MPAMIDR_EL1_PMG_MAX, mpamidr); > + > + return mpam_register_requestor(partid_max, pmg_max); mpam_register_requestor() is exposed until CONFIG_ARM64_MPAM_DRIVER is set. CONFIG_ARM64_MPAM_DRIVER and CONFIG_ARM64_MPAM can be different until PATCH[39/47] is applied. So we need PATCH[39/47] to be applied prior to this patch so that mpam_register_requestor() is always existing and exposed. > +} > +/* Must occur before mpam_msc_driver_init() from subsys_initcall() */ > +arch_initcall(arm64_mpam_register_cpus) Thanks, Gavin