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

[Amit Singh Tomar <amitsinght@marvell.com>]

Hi Ben,

On 2025-11-19 at 17:52:30, Ben Horgan (ben.horgan@arm.com) wrote:
> Hi all,
> 
> Just a handful of minor changes based on v5 review comments. See individual
> patches for change lgos. I haven't asked James to host any branches for this
> revision but please let me know if this would be helpful to anyone. Thanks for
> all the help with reviews and testing.
> 
> Previous cover letter from James:
> 
> 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: (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

Booted it on the MARVELL OCTEON 10 platform, and confirmed that MPAM is enabled properly with:

~ # dmesg | grep -i mpam
[    0.000000] ACPI: MPAM 0x0000000BF826FA98 0002C4 (v01 MRVL   CN106    00000001 MRVL 00000001)
[    8.868206] MPAM enabled with 64 PARTIDs and 1 PMGs

Tested-by: Amit Singh Tomar <amitsinght@marvell.com>

However, while testing DDR bandwidth partitioning (based on mpam/snapshot/v6.18-rc4-v5),
seeing behaviour that doesn’t look consistent with how MPAMCFG_MBW_MIN and
MPAMCFG_MBW_MAX should relate.

For instance, when assigning 10% BW to a partition, the value programmed into
MPAMCFG_MBW_MIN ends up higher than the value in MPAMCFG_MBW_MAX. But MBW_MIN
should always be lower than MBW_MAX, correct? If not, the MPAM resctrl side
likely needs a fix?

~ # cat > bw.sh
mount -t resctrl resctrl /sys/fs/resctrl
cd /sys/fs/resctrl
mkdir p1
cd p1
echo fff > cpus
echo "MB:1=10" > schemata

^C
~ # chmod +x bw.sh
~ # ./bw.sh
~ #  devmem MPAMCFG_MBW_MAX 32
0x00001900
~ # devmem MPAMCFG_MBW_MIN 32
0x0000F200

> 
> What is MPAM? Set your time-machine to 2020:
> https://lore.kernel.org/lkml/20201030161120.227225-1-james.morse@arm.com/
> 
> Ben Horgan (5):
>   ACPI / PPTT: Add acpi_pptt_cache_v1_full to use pptt cache as one
>     structure
>   platform: Define platform_device_put cleanup handler
>   ACPI: Define acpi_put_table cleanup handler and
>     acpi_get_table_pointer() helper
>   arm_mpam: Consider overflow in bandwidth counter state
>   MAINTAINERS: new entry for MPAM Driver
> 
> 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 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
> 
>  MAINTAINERS                         |   10 +
>  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           |  411 ++++
>  drivers/acpi/pptt.c                 |  280 ++-
>  drivers/acpi/tables.c               |    2 +-
>  drivers/resctrl/Kconfig             |   24 +
>  drivers/resctrl/Makefile            |    4 +
>  drivers/resctrl/mpam_devices.c      | 2723 +++++++++++++++++++++++++++
>  drivers/resctrl/mpam_internal.h     |  658 +++++++
>  drivers/resctrl/test_mpam_devices.c |  389 ++++
>  include/linux/acpi.h                |   26 +
>  include/linux/arm_mpam.h            |   66 +
>  include/linux/platform_device.h     |    1 +
>  17 files changed, 4608 insertions(+), 18 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
> 
> -- 
> 2.43.0
>