Subject: Re: [PATCH v3] PCI/TPH: Fix get cpu steer-tag fail on ARM64 platform

From: Jonathan Cameron <[email-masked]>
Date: Fri, 6 Mar 2026 10:01:50 +0000

On Fri, 6 Mar 2026 10:19:17 +0800
Chengwen Feng <[email-masked]> wrote:

> Currently the pcie_tph_get_cpu_st() has an issue on ARM64 platform:
> 1. The pcie_tph_get_cpu_st() function directly uses cpu_uid as the input
>    parameter to call the PCI ACPI DSM method. According to the DSM
>    definition, the input value should be the ACPI Processor UID (see [1]
>    for details).
> 2. In the Broadcom driver implementation [2] (which invokes
>    pcie_tph_get_cpu_st()), cpu_uid is obtained via
>    cpumask_first(irq->cpu_mask) - this is the logical CPU ID of a CPU
>    core, generated and managed by kernel (e.g., [0,255] for a system
>    with 256 logical CPU cores).
> 3. On ARM64 platforms, ACPI assigns Processor UID to cores listed in the
>    MADT table, and this UID may not match the kernel's logical CPU ID.
>    As a result, the current implementation fails to retrieve the correct
>    CPU steer-tag in such cases.
> 4. The function works on AMD x86 platforms only because the logical CPU
>    ID is identical to the ACPI Processor UID on those systems.
> 
> This commit fixes it by:
> 1. For ACPI-enabled platforms, unify the CPU ACPI ID retrieval
>    interface:
>    - On arm64/riscv/loongarch: Rename existing get_acpi_id_for_cpu() to
>      acpi_get_cpu_acpi_id().
>    - On x86: Add new acpi_get_cpu_acpi_id() implementation that wraps
>      cpu_acpi_id().
> 2. Update pcie_tph_get_cpu_st() to use acpi_get_cpu_acpi_id(cpu) to get
>    valid ACPI Processor UID for DSM calls.
> 3. Renaming pcie_tph_get_cpu_st()'s input parameter cpu_uid to cpu for
>    clarity, as the parameter now represents a logical CPU ID (not a
>    UID).
> 
> [1] According to ECN_TPH-ST_Revision_20200924
>     (https://members.pcisig.com/wg/PCI-SIG/document/15470), the input
>     is defined as: "If the target is a processor, then this field
>     represents the ACPI Processor UID of the processor as specified in
>     the MADT. If the target is a processor container, then this field
>     represents the ACPI Processor UID of the processor container as
>     specified in the PPTT."
> [2] commit c214410c47d6e ("bnxt_en: Add TPH support in BNXT driver")
> 
> Fixes: d2e8a34876ce ("PCI/TPH: Add Steering Tag support")
> Cc: [email-masked]
> Signed-off-by: Chengwen Feng <[email-masked]>
> 
> ---
> Changes in v3:
> - Rename existing get_acpi_id_for_cpu() to acpi_get_cpu_acpi_id() other
>   than add one new API.
Ah. I wasn't clear around that rename suggestion.  Split this into two patches.
1) Rename
2) The new stuff plus x86 implementation.

> 
> Changes in v2:
> - Add ECN _DSM reference doc name and its URL.
> - Separate implement acpi_get_cpu_acpi_id() in each arch which supports
>   ACPI.
> - Refine commit-log.
> 
> ---
>  Documentation/PCI/tph.rst          |  4 ++--
>  arch/arm64/include/asm/acpi.h      |  4 ++--
>  arch/loongarch/include/asm/acpi.h  |  2 +-
>  arch/riscv/include/asm/acpi.h      |  2 +-
>  arch/riscv/kernel/acpi_numa.c      |  2 +-
>  arch/x86/include/asm/acpi.h        |  2 ++
>  arch/x86/kernel/cpu/common.c       |  8 ++++++++
>  drivers/acpi/pptt.c                | 16 ++++++++--------
>  drivers/acpi/riscv/rhct.c          |  2 +-
>  drivers/pci/tph.c                  | 11 ++++++-----
>  drivers/perf/arm_cspmu/arm_cspmu.c |  2 +-
>  include/linux/pci-tph.h            |  4 ++--
>  12 files changed, 35 insertions(+), 24 deletions(-)