Re: [PATCH v6 00/34] arm_mpam: Add basic mpam driver

[Punit Agrawal <punit.agrawal@oss.qualcomm.com>]

Hi Ben,

Thanks for getting back.

Ben Horgan <ben.horgan@arm.com> writes:

> Hi Punit,
>
> On 11/24/25 15:21, Punit Agrawal wrote:
>> Hi Ben, James
>> 
>> Ben Horgan <ben.horgan@arm.com> writes:
>> 
>>>
>>> This series is based on v6.18-rc4, and can be retrieved from: (no v6 version)
>>> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/driver/v5
>>>
>>> The rest of the driver can be found here: (no v6 version)
>>> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/snapshot/v6.18-rc4-v5
>>>
>>> What is MPAM? Set your time-machine to 2020:
>>> https://lore.kernel.org/lkml/20201030161120.227225-1-james.morse@arm.com/
>> 
>> Although a little late to the party, I've managed to throw together
>> enough firmware to describe the MPAM hardware and take this set (more
>> specifically mpam/snapshot/v6.18-rc4-v5 branch from James' repository)
>> for a spin. Using the branch, the kernel is able to probe the hardware
>> and discover the advertised features. Yay! We are in business.
>
> Thanks for giving it a go. :)
>
>> 
>> Having said that, there are a few quirks of the platform that run into
>> issues with later patches in the branch. The platform has MSCs attached
>> to shared L2 caches which are being skipped during later stages of
>> initialisation. IIUC, the L2 MSCs' limitations stems from the
>> assumptions in the resctrl interface.
>
> What in particualar is being skipped?

The registration of the discovered MSCs with resctrl and subsequent
exposing it to the user.

>> I was wondering if there are any patches available to relax these
>> limitations? I can give them a try. Or do these need to be put together
>> from the ground up? Any pointers greatly appreciated.
>
> There are some extra things added in the extras branch [1] e.g. cache
> maximum usage controls (cmax). However, lots of possible things are
> still missing e.g. any monitors on L2. If it doesn't fit with the
> topology expected by resctrl then it is unlikely to have been considered
> yet.

Thanks for the pointer. I'll give the snapshot+extras branch[1] a try.

The platform does have both controls and monitors attached to L2. If
this isn't being looked at, I can try and put something together. Thanks
for confirming that the limitation is likely due to resctrl.

Looking forward to the next set of MPAM support landing.

> [1] https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/log/?h=mpam/snapshot%2bextras/v6.18-rc1

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