Re: [PATCH v4 0/8] ACPI: CPPC: Resource Priority Register support and sysfs interface

[Rafael J. Wysocki (Intel)]

+Christian

Christian, can you have a look at this, please?

On Tue, Sep 22, 2026 at 2:43 PM Lifeng Zheng <zhenglifeng1@xxxxxxxxxx> wrote:
>
> This series implements support for the CPPC v4 Resource Priority Register
> mechanism defined in ACPI 6.6, Section 8.4.6.1.2.7, and exposes it to
> userspace via sysfs.
>
> Resource Priority allows OSPM to control the relative priority among
> processors for shared resources. OSPM can utilize these sysfs interfaces
> to configure resource priorities, allowing resources to be preferentially
> allocated to more important tasks.
>
> The controlled resource types include processor boost, throttle, L2 cache,
> L3 cache, and memory bandwidth.  Each Resource Priority group consists of:
>
>   - CONTROLLED_RESOURCES: which resource types the group affects
>   - ENABLE_VALUE / ENABLE_REGISTER: enable/disable the group
>   - PRIORITY_COUNT / PRIORITY_REGISTER: read/write the priority level
>
> The patch series is organized in three parts:
>
>   - patches 1-4 extend the CPPC data structures and _CPC parser to handle
>     Package-type entries and parse Resource Priority sub-packages into
>     structured descriptors.
>
>   - patches 5-7 refactor existing register I/O helpers to support direct
>     register access and add accessor functions for Resource Priority
>     attributes (enable, priority count, priority value).
>
>   - patch 8 creates a "resource_priority" sysfs hierarchy under each
>     cpufreq policy to expose the Resource Priority attributes to userspace.
>
> Changelog:
> v4:
>  - Patch 7: Set *num_resources to 0 when controlled resources number
>    invalid in cppc_get_resource_priority_resources(), therefore, the caller
>    will not read the unassigned `resources` pointer.
>  - Patch 8: Remove kfree() from the error path of
>    cppc_create_res_prio_sysfs() because cppc_res_prio_release() will do it.
>
> v3:
>  - Patch 2: Add the (i - 2) == RESOURCE_PRIORITY condition back to ensure
>    the new code behaves the same as the original.
>  - Patch 4: Assign -ENODATA to ret when an unexpected ACPI_TYPE_PACKAGE
>    appears.
>  - Patch 5: Initialize the `optional` field of the remaining cpc_regs to
>    true so that they are treated as unsupported.
>  - Patch 8: Call cppc_cpufreq_cpu_fie_exit() and set perf to lowest_perf
>    when cppc_create_res_prio_sysfs() fails. Call kobject_put() and kfree()
>    when kobject_init_and_add() fails in cppc_create_res_prio_sysfs().
>  - Link: https://lore.kernel.org/all/20260812015217.74598-1-zhenglifeng1@xxxxxxxxxx/
>
> v2:
>  - Patch 1: Revert changes to the CPC_SUPPORTED() macro.
>  - Link: https://lore.kernel.org/all/20260804085042.4118193-1-zhenglifeng1@xxxxxxxxxx/
>
> v1:
>  - Link: https://lore.kernel.org/all/20260717024502.3520445-1-zhenglifeng1@xxxxxxxxxx/
>
> ---
>
> RFC: sysfs placement
>
> The sysfs interface is currently placed under /sys/devices/system/cpu/cpufreq/
> (i.e. the cpufreq policy directory). I am unsure whether this is the best
> location and would appreciate reviewer feedback.
>
> The concern is that Resource Priority covers resource types beyond CPU
> frequency control:
>
>   - PROCESSOR_BOOST, PROCESSOR_THROTTLE -- clearly CPU-frequency related
>   - L2_CACHE, L3_CACHE -- cache partitioning, not frequency
>   - MEMORY_BANDWIDTH -- memory QoS, not frequency
>
> Placing the attributes under cpufreq makes sense for boost/throttle but
> feels semantically wrong for cache and memory bandwidth resources.
>
> I would appreciate feedback on whether cpufreq is the right home for
> this interface, or whether a different location would be more appropriate.
>
> Lifeng Zheng (8):
>   ACPI: CPPC: Prepare cpc_register_resource for Package-type entries
>   ACPI: CPPC: Refactor element parsing into parse_cpc_element()
>   ACPI: CPPC: Refactor resource cleanup into free_reg_resource()
>   ACPI: CPPC: Parse Resource Priority Register entries from _CPC package
>   ACPI: CPPC: Store optional flag in cpc_register_resource
>   ACPI: CPPC: Factor out cpc_read_reg() and cpc_write_reg()
>   ACPI: CPPC: Add Resource Priority accessors
>   cpufreq: cppc: Expose Resource Priority attributes via sysfs
>
>  drivers/acpi/cppc_acpi.c       | 719 +++++++++++++++++++++++++++------
>  drivers/cpufreq/cppc_cpufreq.c | 281 ++++++++++++-
>  include/acpi/cppc_acpi.h       |  60 +++
>  3 files changed, 930 insertions(+), 130 deletions(-)
>
> --
> 2.33.0
>
>