Message-ID: <e715a048-3d21-4bcf-9fff-f63e6be48d46@arm.com>
Date: Fri, 29 Aug 2025 09:20:57 +0100
From: Ben Horgan <ben.horgan@....com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
 devicetree@...r.kernel.org
Cc: shameerali.kolothum.thodi@...wei.com,
 D Scott Phillips OS <scott@...amperecomputing.com>,
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Subject: Re: [PATCH 07/33] arm64: kconfig: Add Kconfig entry for MPAM

Hi James,

On 8/28/25 16:58, James Morse wrote:
> Hi Ben,
> 
> On 27/08/2025 09:53, Ben Horgan wrote:
>> On 8/22/25 16:29, James Morse wrote:
>>> The bulk of the MPAM driver lives outside the arch code because it
>>> largely manages MMIO devices that generate interrupts. The driver
>>> needs a Kconfig symbol to enable it, as MPAM is only found on arm64
>>> platforms, that is where the Kconfig option makes the most sense.
>>>
>>> This Kconfig option will later be used by the arch code to enable
>>> or disable the MPAM context-switch code, and registering the CPUs
>>> properties with the MPAM driver.
> 
>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>> index e9bbfacc35a6..658e47fc0c5a 100644
>>> --- a/arch/arm64/Kconfig
>>> +++ b/arch/arm64/Kconfig
>>> @@ -2060,6 +2060,23 @@ config ARM64_TLB_RANGE
>>>  	  ARMv8.4-TLBI provides TLBI invalidation instruction that apply to a
>>>  	  range of input addresses.
>>>  
>>> +config ARM64_MPAM
>>> +	bool "Enable support for MPAM"
>>> +	help
>>> +	  Memory Partitioning and Monitoring is an optional extension
>>> +	  that allows the CPUs to mark load and store transactions with
>>> +	  labels for partition-id and performance-monitoring-group.
>>> +	  System components, such as the caches, can use the partition-id
>>> +	  to apply a performance policy. MPAM monitors can use the
>>> +	  partition-id and performance-monitoring-group to measure the
>>> +	  cache occupancy or data throughput.
>>> +
>>> +	  Use of this extension requires CPU support, support in the
>>> +	  memory system components (MSC), and a description from firmware
>>> +	  of where the MSC are in the address space.
>>> +
>>> +	  MPAM is exposed to user-space via the resctrl pseudo filesystem.
>>> +
>>>  endmenu # "ARMv8.4 architectural features"
> 
>> Should this be moved to "ARMv8.2 architectural features" rather than the
>> 8.4 menu? In the arm reference manual, version L.b, I see FEAT_MPAM
>> listed in the section A2.2.3.1 Features added to the Armv8.2 extension
>> in later releases.
> 
> Hmmm, I don't think we've done that anywhere else. I'm only aware of one v8.2 platform
> that had it, and those are not widely available. As it was a headline v8.4 feature I'd
> prefer to keep it there.
> 
> I think its more confusing to put it under v8.2!

Ok, always best to minimise confusion. Keep it in v8.4.
 >
> Thanks,
> 
> James

-- 
Thanks,

Ben

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