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

From: fengchengwen

Date: Thu Mar 05 2026 - 04:14:11 EST

Hi Huacai,

On 3/5/2026 4:53 PM, Huacai Chen wrote:
> 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.

Yes, it indeed simple.

But I prefer to have the acpi_ prefix for such API names because it's a cross-subsystem API reference.

Thanks

>
> 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
>>
>