+ BIT(TPH_ST_DSM_FUNC_INDEX)))
+ return AE_ERROR;
+
+ /* DWORD: feature ID (0 for processor cache ST query) */
+ arg3[0].integer.type = ACPI_TYPE_INTEGER;
+ arg3[0].integer.value = 0;
+
+ /* DWORD: target UID */
+ arg3[1].integer.type = ACPI_TYPE_INTEGER;
+ arg3[1].integer.value = cpu_uid;
+
+ /* QWORD: properties, all 0's */
+ arg3[2].integer.type = ACPI_TYPE_INTEGER;
+ arg3[2].integer.value = 0;
+
+ in_obj.type = ACPI_TYPE_PACKAGE;
+ in_obj.package.count = ARRAY_SIZE(arg3);
+ in_obj.package.elements = arg3;
+
+ out_obj = acpi_evaluate_dsm(handle, &pci_acpi_dsm_guid, 7,
+ TPH_ST_DSM_FUNC_INDEX, &in_obj);
+ if (!out_obj)
+ return AE_ERROR;
+
+ if (out_obj->type != ACPI_TYPE_BUFFER) {
+ ACPI_FREE(out_obj);
+ return AE_ERROR;
+ }
+
+ st_out->value = *((u64 *)(out_obj->buffer.pointer));
+
+ ACPI_FREE(out_obj);
+
+ return AE_OK;
+}
+
/* Update the TPH Requester Enable field of TPH Control Register */
static void set_ctrl_reg_req_en(struct pci_dev *pdev, u8 req_type)
{
@@ -140,6 +253,47 @@ static int write_tag_to_st_table(struct pci_dev *pdev, int index, u16 tag)
return pci_write_config_word(pdev, offset, tag);
}
+/**
+ * pcie_tph_get_cpu_st() - Retrieve Steering Tag for a target memory associated
+ * with a specific CPU
+ * @pdev: PCI device
+ * @mem_type: target memory type (volatile or persistent RAM)
+ * @cpu_uid: associated CPU id
+ * @tag: Steering Tag to be returned
+ *
+ * This function returns the Steering Tag for a target memory that is
+ * associated with a specific CPU as indicated by cpu_uid.
+ *
+ * Returns 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)
+{
+ struct pci_dev *rp;
+ acpi_handle rp_acpi_handle;
+ union st_info info;
+
+ rp = pcie_find_root_port(pdev);
+ if (!rp || !rp->bus || !rp->bus->bridge)
+ return -ENODEV;
+
+ rp_acpi_handle = ACPI_HANDLE(rp->bus->bridge);
+
+ if (tph_invoke_dsm(rp_acpi_handle, cpu_uid, &info) != AE_OK) {
+ *tag = 0;
+ return -EINVAL;
+ }
+
+ *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",
+ (mem_type == TPH_MEM_TYPE_VM) ? "volatile" : "persistent",
+ cpu_uid, *tag);
+
+ return 0;
+}
+EXPORT_SYMBOL(pcie_tph_get_cpu_st);
+
/**
* pcie_tph_set_st_entry() - Set Steering Tag in the ST table entry
* @pdev: PCI device
diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
index a0c93b97090a..c9f33688b9a9 100644
--- a/include/linux/pci-tph.h
+++ b/include/linux/pci-tph.h
@@ -9,9 +9,23 @@
#ifndef LINUX_PCI_TPH_H
#define LINUX_PCI_TPH_H
+/*
+ * According to the ECN for PCI Firmware Spec, Steering Tag can be different
+ * depending on the memory type: Volatile Memory or Persistent Memory. When a
+ * caller query about a target's Steering Tag, it must provide the target's
+ * tph_mem_type. ECN link: https://members.pcisig.com/wg/PCI-SIG/document/15470.
+ */
+enum tph_mem_type {
+ TPH_MEM_TYPE_VM, /* volatile memory */
+ TPH_MEM_TYPE_PM /* persistent memory */
+};
+
#ifdef CONFIG_PCIE_TPH
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);
bool pcie_tph_enabled(struct pci_dev *pdev);
void pcie_disable_tph(struct pci_dev *pdev);
int pcie_enable_tph(struct pci_dev *pdev, int mode);
@@ -20,6 +34,10 @@ int pcie_tph_modes(struct pci_dev *pdev);
static inline int pcie_tph_set_st_entry(struct pci_dev *pdev,
unsigned int index, u16 tag)
{ 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)
+{ return -EINVAL; }
static inline bool pcie_tph_enabled(struct pci_dev *pdev) { return false; }
static inline void pcie_disable_tph(struct pci_dev *pdev) { }
static inline int pcie_enable_tph(struct pci_dev *pdev, int mode)
