Re: [PATCH RFC 00/15] arm-mpam: Add basic device tree support for resctrl

[Yin Li <yin.li@oss.qualcomm.com>]

On 8/11/2026 9:30 PM, Yin Li wrote:
> Notes for James, Shanker and Rob
> --------------------------------
> This series builds directly on your not-yet-upstream MPAM snapshot
> patches from the mpam/snapshot+extras/v6.18-rc1 branch. Two things I'd
> like your guidance on:
> 
> 1. Do you mind us picking these up and continuing to extend them? We have
>     kept the original authorship and Signed-off-by intact and documented
>     the inherited-vs-new split below. If you would prefer a different
>     attribution arrangement, or have your own plans to upstream MPAM DT
>     support, please let us know so we can avoid duplicating effort.
> 
> 2. The fixes to the inherited patches are kept as small, self-contained
>     patches on top, purely to make review easier. Since fixes to
>     not-yet-upstream patches would normally be squashed into the original
>     commit by its author, please point out which of these you would like
>     folded back, and we will reorganize accordingly.
> 
> Rob kindly provided some early off-list feedback on an earlier draft,
> which this series has tried to address.
> 
> Add Arm MPAM resctrl basic device tree support.
> 
> Arm Memory System Resource Partitioning and Monitoring (MPAM) with
> resctrl requires device tree (DT) support as a prerequisite before any
> higher-level functionality can be enabled. This series provides the
> foundational DT binding and parsing support for MPAM, laying the
> groundwork for subsequent features such as MPAM Firmware-backed
> (MPAM-FB) partitioning.
> 

Hi all,

Just a friendly ping on this RFC series.

In particular, I'd appreciate any guidance on whether this is a
reasonable direction for upstream DT support of MPAM/resctrl, before
spending more effort preparing the next revision.

Any high-level feedback would be very helpful.

Thanks for your time.



> The patches are based on earlier work by James Morse, Shanker
> Donthineni and Rob Herring, with fixes and additions on top:
> 
> Inherited (authorship preserved, with fixes noted in each patch):
> - dt-bindings: MPAM MSC binding [1]
> - cacheinfo: expose cache-id generation from a device_node [2]
> - arm_mpam: device tree support for MSC probing [3]
> - arm_mpam: memory controller MSC support on DT platforms [4]
> 
> New on top:
> - standalone fixes extracted from the inherited patches (device_node
>    refcount, cache-id sentinel/type, RIS index range checks, MSC window
>    size, accessibility return type, foundling MSC creation, cache-id
>    error path)
> - dt-bindings: schema and example fixes
> - arm_mpam: derive MSC accessibility from per-RIS nodes as a fallback
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/commit/?h=mpam/snapshot+extras/v6.18-rc1&id=b38bed339681
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/commit/?h=mpam/snapshot+extras/v6.18-rc1&id=2af39084438c
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/commit/?h=mpam/snapshot+extras/v6.18-rc1&id=a6ab8b6c77cb
> [4] https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/commit/?h=mpam/snapshot+extras/v6.18-rc1&id=c1be40782ace
> 
> DT affinity model
> -----------------
> An MSC node is nested under the device it partitions or monitors. For a
> cache MSC this is the cache node, so the MSC's CPU affinity is derived
> from its parent cache; for a memory-controller MSC the parent is the
> memory device, which is accessible from all CPUs. A per-RIS fallback is
> also provided: when an MSC sits under a generic container with no
> affinity-bearing parent, affinity is resolved from an explicit 'cpus'
> phandle or an 'arm,mpam-device' phandle on each RIS node.
> 
> The Kaanapali DTS patch is for local enabling and verification only and
> cannot be upstreamed: the platform is already upstream with a public
> device tree, and production firmware does not allow the OS to write the
> MSC registers, so this path only works on a local test setup. The MSC
> nodes are disabled by default, serving as a reference example for other
> platform DT authors.
> 
> Signed-off-by: Yin Li <yin.li@oss.qualcomm.com>
> ---
> To: James Morse <james.morse@arm.com>
> To: Rob Herring <robh@kernel.org>
> To: Shanker Donthineni <sdonthineni@nvidia.com>
> To: Krzysztof Kozlowski <krzk+dt@kernel.org>
> To: Ben Horgan <ben.horgan@arm.com>
> To: Conor Dooley <conor+dt@kernel.org>
> To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> To: "Rafael J. Wysocki" <rafael@kernel.org>
> To: Danilo Krummrich <dakr@kernel.org>
> To: Reinette Chatre <reinette.chatre@intel.com>
> To: Fenghua Yu <fenghuay@nvidia.com>
> To: Bjorn Andersson <andersson@kernel.org>
> To: Konrad Dybcio <konradybcio@kernel.org>
> Cc: trilok.soni@oss.qualcomm.com
> Cc: aiqun.yu@oss.qualcomm.com
> Cc: ganapatrao.kulkarni@oss.qualcomm.com
> Cc: Srivathsa L Rao <srivathsa.rao@oss.qualcomm.com>
> Cc: linux-arm-msm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: driver-core@lists.linux.dev
> Cc: devicetree@vger.kernel.org
> Cc: trilok.soni@oss.qualcomm.com
> Cc: aiqun.yu@oss.qualcomm.com
> Cc: ganapatrao.kulkarni@oss.qualcomm.com
> Cc: Srivathsa L Rao <srivathsa.rao@oss.qualcomm.com>
> 
> ---
> James Morse (2):
>        cacheinfo: Expose the code to generate a cache-id from a device_node
>        arm_mpam: Add device tree support for MSC probing
> 
> Rob Herring (1):
>        dt-bindings: arm: Add MPAM MSC binding
> 
> Shanker Donthineni (1):
>        arm_mpam: Add support for memory controller MSC on DT platforms
> 
> Yin Li (11):
>        arm_mpam: Fix device_node refcount in DT resource parsing
>        arm_mpam: Fix cache ID sentinel from ~0UL to U32_MAX to match u32 return type
>        arm_mpam: Fix the RIS index range check in mpam_ris_create_locked
>        arm_mpam: Fix ris_idx type to prevent range check bypass on truncation
>        arm_mpam: Fix MSC MMIO window size to use resource_size() instead of end - start
>        arm_mpam: Fix update_msc_accessibility() return type to void
>        arm_mpam: Fix mpam_dt_create_foundling_msc() to create MSC platform devices
>        arm_mpam: Fix get_cpumask_from_cache() to clear mask on error
>        dt-bindings: arm: Fix MPAM MSC binding schema and examples
>        arm_mpam: Support MSC accessibility derivation from RIS nodes
>        [DNM] arm64: dts: qcom: kaanapali: Add MPAM MSC nodes for the L2 caches
> 
>   .../devicetree/bindings/arm/arm,mpam-msc.yaml      | 202 +++++++++++
>   arch/arm64/boot/dts/qcom/kaanapali.dtsi            |  50 ++-
>   drivers/base/cacheinfo.c                           |  19 +-
>   drivers/resctrl/mpam_devices.c                     | 401 +++++++++++++++++++--
>   drivers/resctrl/mpam_internal.h                    |   2 +-
>   include/linux/arm_mpam.h                           |   4 +-
>   include/linux/cacheinfo.h                          |   3 +
>   7 files changed, 638 insertions(+), 43 deletions(-)
> ---
> base-commit: 3d08ff75a47a3e7e2ab45a3bcab6723b4d906422
> change-id: 20260731-mpam-resctrl-dt-knp-support-c15dcc3a4a98
> 
> Best regards,
> --
> Yin Li <yin.li@oss.qualcomm.com>
> 

-- 
Thx and BRs,
Yin