linux-kernel - Re: [PATCH 12/33] arm_mpam: Add the class and component structures for ris firmware described

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Message-ID: <cdd07b6e-5cc5-407f-b55b-75f230a2e786@arm.com>
Date: Wed, 10 Sep 2025 20:32:42 +0100
From: James Morse <james.morse@....com>
To: Ben Horgan <ben.horgan@....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>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
 Dave Martin <dave.martin@....com>, Koba Ko <kobak@...dia.com>,
 Shanker Donthineni <sdonthineni@...dia.com>, fenghuay@...dia.com,
 baisheng.gao@...soc.com, Jonathan Cameron <jonathan.cameron@...wei.com>,
 Rob Herring <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
 Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH 12/33] arm_mpam: Add the class and component structures
 for ris firmware described

Hi Ben,

On 29/08/2025 13:41, Ben Horgan wrote:
> On 8/22/25 16:30, James Morse wrote:
>> An MSC is a container of resources, each identified by their RIS index.
>> Some RIS are described by firmware to provide their position in the system.
>> Others are discovered when the driver probes the hardware.
>>
>> To configure a resource it needs to be found by its class, e.g. 'L2'.
>> There are two kinds of grouping, a class is a set of components, which
>> are visible to user-space as there are likely to be multiple instances
>> of the L2 cache. (e.g. one per cluster or package)
>>
>> struct mpam_components are a set of struct mpam_vmsc. A vMSC groups the
>> RIS in an MSC that control the same logical piece of hardware. (e.g. L2).
>> This is to allow hardware implementations where two controls are presented
>> as different RIS. Re-combining these RIS allows their feature bits to
>> be or-ed. This structure is not visible outside mpam_devices.c
>>
>> struct mpam_vmsc are then a set of struct mpam_msc_ris, which are not
>> visible as each L2 cache may be composed of individual slices which need
>> to be configured the same as the hardware is not able to distribute the
>> configuration.
>>
>> Add support for creating and destroying these structures.
>>
>> A gfp is passed as the structures may need creating when a new RIS entry
>> is discovered when probing the MSC.

>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index 71a1fb1a9c75..5baf2a8786fb 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -179,7 +650,10 @@ static int update_msc_accessibility(struct mpam_msc *msc)
>>  		cpumask_copy(&msc->accessibility, cpu_possible_mask);
>>  		err = 0;
>>  	} else {
>> -		if (of_device_is_compatible(parent, "memory")) {
>> +		if (of_device_is_compatible(parent, "cache")) {
>> +			err = get_cpumask_from_cache(parent,
>> +						     &msc->accessibility);
>> +		} else if (of_device_is_compatible(parent, "memory")) {

> The determination of the accessibility for the h/w msc doesn't fit with
> the subject of this patch. Could this hunk and the supporting functions
> be split into a precursor patch?

I've moved this bit into the previous patches.


Thanks,

James