Re: [PATCH v2] PCI/TPH: Fix get cpu steer-tag fail on ARM64 platform

[Huacai Chen]

Hi, Chengwen,

On Thu, Mar 5, 2026 at 4:37 PM Chengwen Feng <fengchengwen@xxxxxxxxxx> 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. Introducing acpi_get_cpu_acpi_id() in all ACPI-enabled platforms.
>    This new API calls get_acpi_id_for_cpu() to retrieve the ACPI
>    Processor UID on arm64/riscv/loongarch arch, and it calls
>    cpu_acpi_id() on x86 arch.
> 2. 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@xxxxxxxxxxxxxxx
> Signed-off-by: Chengwen Feng <fengchengwen@xxxxxxxxxx>
>
> ---
> 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/kernel/acpi.c     |  9 +++++++++
>  arch/loongarch/kernel/acpi.c |  9 +++++++++
>  arch/riscv/kernel/acpi.c     | 10 ++++++++++
>  arch/x86/kernel/cpu/common.c | 17 +++++++++++++++++
>  drivers/pci/tph.c            | 17 ++++++++++++-----
>  include/linux/acpi.h         | 10 ++++++++++
>  include/linux/pci-tph.h      |  4 ++--
>  8 files changed, 71 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/PCI/tph.rst b/Documentation/PCI/tph.rst
> index e8993be64fd6..b6cf22b9bd90 100644
> --- a/Documentation/PCI/tph.rst
> +++ b/Documentation/PCI/tph.rst
> @@ -79,10 +79,10 @@ To retrieve a Steering Tag for a target memory associated with a specific
>  CPU, use the following function::
>
>    int pcie_tph_get_cpu_st(struct pci_dev *pdev, enum tph_mem_type type,
> -                          unsigned int cpu_uid, u16 *tag);
> +                          unsigned int cpu, u16 *tag);
>
>  The `type` argument is used to specify the memory type, either volatile
> -or persistent, of the target memory. The `cpu_uid` argument specifies the
> +or persistent, of the target memory. The `cpu` argument specifies the
>  CPU where the memory is associated to.
>
>  After the ST value is retrieved, the device driver can use the following
> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> index af90128cfed5..e7d4d9bd3036 100644
> --- a/arch/arm64/kernel/acpi.c
> +++ b/arch/arm64/kernel/acpi.c
> @@ -29,6 +29,7 @@
>  #include <linux/suspend.h>
>  #include <linux/pgtable.h>
>
> +#include <acpi/acpi.h>
>  #include <acpi/ghes.h>
>  #include <acpi/processor.h>
>  #include <asm/cputype.h>
> @@ -458,3 +459,11 @@ int acpi_unmap_cpu(int cpu)
>  }
>  EXPORT_SYMBOL(acpi_unmap_cpu);
>  #endif /* CONFIG_ACPI_HOTPLUG_CPU */
> +
> +int acpi_get_cpu_acpi_id(unsigned int cpu)
> +{
> +       if (cpu >= nr_cpu_ids || !cpu_possible(cpu))
> +               return -EINVAL;
> +       return get_acpi_id_for_cpu(cpu);
> +}
> +EXPORT_SYMBOL_GPL(acpi_get_cpu_acpi_id);
> diff --git a/arch/loongarch/kernel/acpi.c b/arch/loongarch/kernel/acpi.c
> index 1367ca759468..db28747a18e8 100644
> --- a/arch/loongarch/kernel/acpi.c
> +++ b/arch/loongarch/kernel/acpi.c
> @@ -16,6 +16,7 @@
>  #include <linux/memblock.h>
>  #include <linux/of_fdt.h>
>  #include <linux/serial_core.h>
> +#include <asm/acpi.h>
>  #include <asm/io.h>
>  #include <asm/numa.h>
>  #include <asm/loongson.h>
> @@ -385,3 +386,11 @@ int acpi_unmap_cpu(int cpu)
>  EXPORT_SYMBOL(acpi_unmap_cpu);
>
>  #endif /* CONFIG_ACPI_HOTPLUG_CPU */
> +
> +int acpi_get_cpu_acpi_id(unsigned int cpu)
> +{
> +       if (cpu >= nr_cpu_ids || !cpu_possible(cpu))
> +               return -EINVAL;
> +       return get_acpi_id_for_cpu(cpu);
> +}
> +EXPORT_SYMBOL_GPL(acpi_get_cpu_acpi_id);
> diff --git a/arch/riscv/kernel/acpi.c b/arch/riscv/kernel/acpi.c
> index 71698ee11621..287c25e79347 100644
> --- a/arch/riscv/kernel/acpi.c
> +++ b/arch/riscv/kernel/acpi.c
> @@ -22,6 +22,8 @@
>  #include <linux/pci.h>
>  #include <linux/serial_core.h>
>
> +#include <asm/acpi.h>
> +
>  int acpi_noirq = 1;            /* skip ACPI IRQ initialization */
>  int acpi_disabled = 1;
>  EXPORT_SYMBOL(acpi_disabled);
> @@ -337,3 +339,11 @@ int raw_pci_write(unsigned int domain, unsigned int bus,
>  }
>
>  #endif /* CONFIG_PCI */
> +
> +int acpi_get_cpu_acpi_id(unsigned int cpu)
> +{
> +       if (cpu >= nr_cpu_ids || !cpu_possible(cpu))
> +               return -EINVAL;
> +       return get_acpi_id_for_cpu(cpu);
> +}
> +EXPORT_SYMBOL_GPL(acpi_get_cpu_acpi_id);
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 1c3261cae40c..9b06c76d5c0c 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -28,6 +28,7 @@
>  #include <linux/stackprotector.h>
>  #include <linux/utsname.h>
>  #include <linux/efi.h>
> +#include <linux/acpi.h>
>
>  #include <asm/alternative.h>
>  #include <asm/cmdline.h>
> @@ -57,6 +58,7 @@
>  #include <asm/asm.h>
>  #include <asm/bugs.h>
>  #include <asm/cpu.h>
> +#include <asm/smp.h>
>  #include <asm/mce.h>
>  #include <asm/msr.h>
>  #include <asm/cacheinfo.h>
> @@ -2643,3 +2645,18 @@ void __init arch_cpu_finalize_init(void)
>          */
>         mem_encrypt_init();
>  }
> +
> +int acpi_get_cpu_acpi_id(unsigned int cpu)
> +{
> +       u32 acpi_id;
> +
> +       if (cpu >= nr_cpu_ids || !cpu_possible(cpu))
> +               return -EINVAL;
> +
> +       acpi_id = cpu_acpi_id(cpu);
> +       if (acpi_id == CPU_ACPIID_INVALID)
> +               return -ENODEV;
> +
> +       return (int)acpi_id;
> +}
> +EXPORT_SYMBOL_GPL(acpi_get_cpu_acpi_id);
> diff --git a/drivers/pci/tph.c b/drivers/pci/tph.c
> index ca4f97be7538..3cd38972fcb1 100644
> --- a/drivers/pci/tph.c
> +++ b/drivers/pci/tph.c
> @@ -236,21 +236,28 @@ static int write_tag_to_st_table(struct pci_dev *pdev, int index, u16 tag)
>   * with a specific CPU
>   * @pdev: PCI device
>   * @mem_type: target memory type (volatile or persistent RAM)
> - * @cpu_uid: associated CPU id
> + * @cpu: associated CPU id
>   * @tag: Steering Tag to be returned
>   *
>   * Return the Steering Tag for a target memory that is associated with a
> - * specific CPU as indicated by cpu_uid.
> + * specific CPU as indicated by cpu.
>   *
>   * Return: 0 if success, otherwise negative value (-errno)
>   */
>  int pcie_tph_get_cpu_st(struct pci_dev *pdev, enum tph_mem_type mem_type,
> -                       unsigned int cpu_uid, u16 *tag)
> +                       unsigned int cpu, u16 *tag)
>  {
>  #ifdef CONFIG_ACPI
> +       unsigned int cpu_uid;
>         struct pci_dev *rp;
>         acpi_handle rp_acpi_handle;
>         union st_info info;
> +       int ret;
> +
> +       ret = acpi_get_cpu_acpi_id(cpu);
Can we use get_acpi_id_for_cpu() directly? Then just x86 needs a wrapper.

Huacai

> +       if (ret < 0)
> +               return ret;
> +       cpu_uid = (unsigned int)ret;
>
>         rp = pcie_find_root_port(pdev);
>         if (!rp || !rp->bus || !rp->bus->bridge)
> @@ -265,9 +272,9 @@ int pcie_tph_get_cpu_st(struct pci_dev *pdev, enum tph_mem_type mem_type,
>
>         *tag = tph_extract_tag(mem_type, pdev->tph_req_type, &info);
>
> -       pci_dbg(pdev, "get steering tag: mem_type=%s, cpu_uid=%d, tag=%#04x\n",
> +       pci_dbg(pdev, "get steering tag: mem_type=%s, cpu=%d, tag=%#04x\n",
>                 (mem_type == TPH_MEM_TYPE_VM) ? "volatile" : "persistent",
> -               cpu_uid, *tag);
> +               cpu, *tag);
>
>         return 0;
>  #else
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 4d2f0bed7a06..426fb4dca333 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -324,6 +324,16 @@ int acpi_unmap_cpu(int cpu);
>
>  acpi_handle acpi_get_processor_handle(int cpu);
>
> +/*
> + * acpi_get_cpu_acpi_id() - Get ACPI Processor UID of a specified CPU from MADT table
> + * @cpu: Logical CPU number (0-based)
> + *
> + * Return: ACPI Processor ID of the CPU on success (non-negative);
> + *         -EINVAL if the CPU number is invalid or not possible;
> + *         -ENODEV if the ACPI ID of the CPU is invalid.
> + */
> +int acpi_get_cpu_acpi_id(unsigned int cpu);
> +
>  #ifdef CONFIG_ACPI_HOTPLUG_IOAPIC
>  int acpi_get_ioapic_id(acpi_handle handle, u32 gsi_base, u64 *phys_addr);
>  #endif
> diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
> index ba28140ce670..be68cd17f2f8 100644
> --- a/include/linux/pci-tph.h
> +++ b/include/linux/pci-tph.h
> @@ -25,7 +25,7 @@ int pcie_tph_set_st_entry(struct pci_dev *pdev,
>                           unsigned int index, u16 tag);
>  int pcie_tph_get_cpu_st(struct pci_dev *dev,
>                         enum tph_mem_type mem_type,
> -                       unsigned int cpu_uid, u16 *tag);
> +                       unsigned int cpu, u16 *tag);
>  void pcie_disable_tph(struct pci_dev *pdev);
>  int pcie_enable_tph(struct pci_dev *pdev, int mode);
>  u16 pcie_tph_get_st_table_size(struct pci_dev *pdev);
> @@ -36,7 +36,7 @@ static inline int pcie_tph_set_st_entry(struct pci_dev *pdev,
>  { return -EINVAL; }
>  static inline int pcie_tph_get_cpu_st(struct pci_dev *dev,
>                                       enum tph_mem_type mem_type,
> -                                     unsigned int cpu_uid, u16 *tag)
> +                                     unsigned int cpu, u16 *tag)
>  { return -EINVAL; }
>  static inline void pcie_disable_tph(struct pci_dev *pdev) { }
>  static inline int pcie_enable_tph(struct pci_dev *pdev, int mode)
> --
> 2.17.1
>