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

[fengchengwen]

On 3/6/2026 6:01 PM, Jonathan Cameron wrote:
> On Fri, 6 Mar 2026 10:19:17 +0800
> Chengwen Feng <fengchengwen at huawei.com> 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: stable at vger.kernel.org
>> Signed-off-by: Chengwen Feng <fengchengwen at huawei.com>
>>
>> ---
>> 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.

Hi Jonathan,

All fixes are applied in v4. Please review.

Thanks.

> 
>>
>> 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(-)
> 
> 
>