linux-kernel - Re: [PATCH v3 00/29] arm_mpam: Add basic mpam driver

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Message-ID: <CALPaoCjbDyvRbW2bcrhB3opF1ieDLhv1961Gr7vYv=k-nzC27Q@mail.gmail.com>
Date: Wed, 5 Nov 2025 10:39:17 +0100
From: Peter Newman <peternewman@...gle.com>
To: James Morse <james.morse@....com>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-acpi@...r.kernel.org, 
	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>, dfustini@...libre.com, amitsinght@...vell.com, 
	David Hildenbrand <david@...hat.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>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Danilo Krummrich <dakr@...nel.org>, Jeremy Linton <jeremy.linton@....com>, Gavin Shan <gshan@...hat.com>
Subject: Re: [PATCH v3 00/29] arm_mpam: Add basic mpam driver

Hi James,

On Fri, Oct 17, 2025 at 8:57 PM James Morse <james.morse@....com> wrote:
>
> Hello,
>
> A slew of minor changes, nothing really sticks out.
> Changes are noted on each patch.
>
> ~
>
> This is just enough MPAM driver for ACPI. DT got ripped out. If you need DT
> support - please share your DTS so the DT folk know the binding is what is
> needed.
> This doesn't contain any of the resctrl code, meaning you can't actually drive it
> from user-space yet. Because of that, its hidden behind CONFIG_EXPERT.
> This will change once the user interface is connected up.
>
> This is the initial group of patches that allows the resctrl code to be built
> on top. Including that will increase the number of trees that may need to
> coordinate, so breaking it up make sense.
>
> The locking got simplified, but is still strange - this is because of the 'mpam-fb'
> firmware interface specification that is still alpha. That thing needs to wait for
> an interrupt after every system register write, which significantly impacts the
> driver. Some features just won't work, e.g. reading the monitor registers via
> perf.
>
> I've not found a platform that can test all the behaviours around the monitors,
> so this is where I'd expect the most bugs.
>
> The MPAM spec that describes all the system and MMIO registers can be found here:
> https://developer.arm.com/documentation/ddi0598/db/?lang=en
> (Ignored the 'RETIRED' warning - that is just arm moving the documentation around.
>  This document has the best overview)
>
> The expectation is this will go via the arm64 tree.
>
>
> This series is based on v6.18-rc4, and can be retrieved from:
> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/driver/v3
>
> The rest of the driver can be found here:
> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/snapshot/v6.18-rc1
>
> What is MPAM? Set your time-machine to 2020:
> https://lore.kernel.org/lkml/20201030161120.227225-1-james.morse@arm.com/
>
> This series was previously posted here:
> [v2] lore.kernel.org/r/20250910204309.20751-1-james.morse@....com
> [v1] lore.kernel.org/r/20250822153048.2287-1-james.morse@....com
> [RFC] lore.kernel.org/r/20250711183648.30766-2-james.morse@....com
>
>
> James Morse (27):
>   ACPI / PPTT: Add a helper to fill a cpumask from a processor container
>   ACPI / PPTT: Stop acpi_count_levels() expecting callers to clear
>     levels
>   ACPI / PPTT: Find cache level by cache-id
>   ACPI / PPTT: Add a helper to fill a cpumask from a cache_id
>   arm64: kconfig: Add Kconfig entry for MPAM
>   ACPI / MPAM: Parse the MPAM table
>   arm_mpam: Add probe/remove for mpam msc driver and kbuild boiler plate
>   arm_mpam: Add the class and component structures for firmware
>     described ris
>   arm_mpam: Add MPAM MSC register layout definitions
>   arm_mpam: Add cpuhp callbacks to probe MSC hardware
>   arm_mpam: Probe hardware to find the supported partid/pmg values
>   arm_mpam: Add helpers for managing the locking around the mon_sel
>     registers
>   arm_mpam: Probe the hardware features resctrl supports
>   arm_mpam: Merge supported features during mpam_enable() into
>     mpam_class
>   arm_mpam: Reset MSC controls from cpuhp callbacks
>   arm_mpam: Add a helper to touch an MSC from any CPU
>   arm_mpam: Extend reset logic to allow devices to be reset any time
>   arm_mpam: Register and enable IRQs
>   arm_mpam: Use a static key to indicate when mpam is enabled
>   arm_mpam: Allow configuration to be applied and restored during cpu
>     online
>   arm_mpam: Probe and reset the rest of the features
>   arm_mpam: Add helpers to allocate monitors
>   arm_mpam: Add mpam_msmon_read() to read monitor value
>   arm_mpam: Track bandwidth counter state for overflow and power
>     management
>   arm_mpam: Add helper to reset saved mbwu state
>   arm_mpam: Add kunit test for bitmap reset
>   arm_mpam: Add kunit tests for props_mismatch()
>
> Rohit Mathew (2):
>   arm_mpam: Probe for long/lwd mbwu counters
>   arm_mpam: Use long MBWU counters if supported
>
>  arch/arm64/Kconfig                  |   25 +
>  drivers/Kconfig                     |    2 +
>  drivers/Makefile                    |    1 +
>  drivers/acpi/arm64/Kconfig          |    3 +
>  drivers/acpi/arm64/Makefile         |    1 +
>  drivers/acpi/arm64/mpam.c           |  384 ++++
>  drivers/acpi/pptt.c                 |  248 ++-
>  drivers/acpi/tables.c               |    2 +-
>  drivers/resctrl/Kconfig             |   22 +
>  drivers/resctrl/Makefile            |    4 +
>  drivers/resctrl/mpam_devices.c      | 2701 +++++++++++++++++++++++++++
>  drivers/resctrl/mpam_internal.h     |  661 +++++++
>  drivers/resctrl/test_mpam_devices.c |  389 ++++
>  include/linux/acpi.h                |   26 +
>  include/linux/arm_mpam.h            |   58 +
>  include/linux/platform_device.h     |    1 +
>  16 files changed, 4519 insertions(+), 9 deletions(-)
>  create mode 100644 drivers/acpi/arm64/mpam.c
>  create mode 100644 drivers/resctrl/Kconfig
>  create mode 100644 drivers/resctrl/Makefile
>  create mode 100644 drivers/resctrl/mpam_devices.c
>  create mode 100644 drivers/resctrl/mpam_internal.h
>  create mode 100644 drivers/resctrl/test_mpam_devices.c
>  create mode 100644 include/linux/arm_mpam.h
>
> --
> 2.39.5
>

I applied this series and booted the kernel on a Google Cloud C4A host
(baremetal) and confirmed through sysfs that all MSCs were probed
successfully.

Tested-by: Peter Newman <peternewman@...gle.com>

Thanks!
-Peter