PCI/TPH: Add Steering Tag support

Add pcie_tph_get_cpu_st() to allow a caller to retrieve Steering Tags for a
target memory associated with a specific CPU. The ST tag is retrieved by
invoking PCI ACPI "_DSM to Query Cache Locality TPH Features" method
(rev=0x7, func=0xF) of the device's Root Port device.

Add pcie_tph_set_st_entry() to update the device's Steering Tags. The tags
will be written into the device's MSI-X table or the ST table located in
the TPH Extended Capability space.

Co-developed-by: Eric Van Tassell <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Eric Van Tassell <[e-mail]>
Signed-off-by: Wei Huang <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Ajit Khaparde <[e-mail]>
Reviewed-by: Somnath Kotur <[e-mail]>
Reviewed-by: Andy Gospodarek <[e-mail]>

drivers/pci/tph.c

···
  *     Wei Huang <[e-mail]>
  */
 #include <linux/pci.h>
+#include <linux/pci-acpi.h>
+#include <linux/msi.h>
 #include <linux/bitfield.h>
 #include <linux/pci-tph.h>
 
···
 
 /* System-wide TPH disabled */
 static bool pci_tph_disabled;
+
+#ifdef CONFIG_ACPI
+/*
+ * The st_info struct defines the Steering Tag (ST) info returned by the
+ * firmware PCI ACPI _DSM method (rev=0x7, func=0xF, "_DSM to Query Cache
+ * Locality TPH Features"), as specified in the approved ECN for PCI Firmware
+ * Spec and available at https://members.pcisig.com/wg/PCI-SIG/document/15470.
+ *
+ * @vm_st_valid:  8-bit ST for volatile memory is valid
+ * @vm_xst_valid: 16-bit extended ST for volatile memory is valid
+ * @vm_ph_ignore: 1 => PH was and will be ignored, 0 => PH should be supplied
+ * @vm_st:        8-bit ST for volatile mem
+ * @vm_xst:       16-bit extended ST for volatile mem
+ * @pm_st_valid:  8-bit ST for persistent memory is valid
+ * @pm_xst_valid: 16-bit extended ST for persistent memory is valid
+ * @pm_ph_ignore: 1 => PH was and will be ignored, 0 => PH should be supplied
+ * @pm_st:        8-bit ST for persistent mem
+ * @pm_xst:       16-bit extended ST for persistent mem
+ */
+union st_info {
+	struct {
+		u64 vm_st_valid : 1;
+		u64 vm_xst_valid : 1;
+		u64 vm_ph_ignore : 1;
+		u64 rsvd1 : 5;
+		u64 vm_st : 8;
+		u64 vm_xst : 16;
+		u64 pm_st_valid : 1;
+		u64 pm_xst_valid : 1;
+		u64 pm_ph_ignore : 1;
+		u64 rsvd2 : 5;
+		u64 pm_st : 8;
+		u64 pm_xst : 16;
+	};
+	u64 value;
+};
+
+static u16 tph_extract_tag(enum tph_mem_type mem_type, u8 req_type,
+			   union st_info *info)
+{
+	switch (req_type) {
+	case PCI_TPH_REQ_TPH_ONLY: /* 8-bit tag */
+		switch (mem_type) {
+		case TPH_MEM_TYPE_VM:
+			if (info->vm_st_valid)
+				return info->vm_st;
+			break;
+		case TPH_MEM_TYPE_PM:
+			if (info->pm_st_valid)
+				return info->pm_st;
+			break;
+		}
+		break;
+	case PCI_TPH_REQ_EXT_TPH: /* 16-bit tag */
+		switch (mem_type) {
+		case TPH_MEM_TYPE_VM:
+			if (info->vm_xst_valid)
+				return info->vm_xst;
+			break;
+		case TPH_MEM_TYPE_PM:
+			if (info->pm_xst_valid)
+				return info->pm_xst;
+			break;
+		}
+		break;
+	default:
+		return 0;
+	}
+
+	return 0;
+}
+
+#define TPH_ST_DSM_FUNC_INDEX	0xF
+static acpi_status tph_invoke_dsm(acpi_handle handle, u32 cpu_uid,
+				  union st_info *st_out)
+{
+	union acpi_object arg3[3], in_obj, *out_obj;
+
+	if (!acpi_check_dsm(handle, &pci_acpi_dsm_guid, 7,
+			    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;
+}
+#endif
+
+/* Update the TPH Requester Enable field of TPH Control Register */
+static void set_ctrl_reg_req_en(struct pci_dev *pdev, u8 req_type)
+{
+	u32 reg;
+
+	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CTRL, &reg);
+
+	reg &= ~PCI_TPH_CTRL_REQ_EN_MASK;
+	reg |= FIELD_PREP(PCI_TPH_CTRL_REQ_EN_MASK, req_type);
+
+	pci_write_config_dword(pdev, pdev->tph_cap + PCI_TPH_CTRL, reg);
+}
 
 static u8 get_st_modes(struct pci_dev *pdev)
 {
···
 	reg &= PCI_TPH_CAP_ST_NS | PCI_TPH_CAP_ST_IV | PCI_TPH_CAP_ST_DS;
 
 	return reg;
+}
+
+static u32 get_st_table_loc(struct pci_dev *pdev)
+{
+	u32 reg;
+
+	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CAP, &reg);
+
+	return FIELD_GET(PCI_TPH_CAP_LOC_MASK, reg);
+}
+
+/*
+ * Return the size of ST table. If ST table is not in TPH Requester Extended
+ * Capability space, return 0. Otherwise return the ST Table Size + 1.
+ */
+static u16 get_st_table_size(struct pci_dev *pdev)
+{
+	u32 reg;
+	u32 loc;
+
+	/* Check ST table location first */
+	loc = get_st_table_loc(pdev);
+
+	/* Convert loc to match with PCI_TPH_LOC_* defined in pci_regs.h */
+	loc = FIELD_PREP(PCI_TPH_CAP_LOC_MASK, loc);
+	if (loc != PCI_TPH_LOC_CAP)
+		return 0;
+
+	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CAP, &reg);
+
+	return FIELD_GET(PCI_TPH_CAP_ST_MASK, reg) + 1;
 }
 
 /* Return device's Root Port completer capability */
···
 
 	return FIELD_GET(PCI_EXP_DEVCAP2_TPH_COMP_MASK, reg);
 }
+
+/* Write ST to MSI-X vector control reg - Return 0 if OK, otherwise -errno */
+static int write_tag_to_msix(struct pci_dev *pdev, int msix_idx, u16 tag)
+{
+#ifdef CONFIG_PCI_MSI
+	struct msi_desc *msi_desc = NULL;
+	void __iomem *vec_ctrl;
+	u32 val;
+	int err = 0;
+
+	msi_lock_descs(&pdev->dev);
+
+	/* Find the msi_desc entry with matching msix_idx */
+	msi_for_each_desc(msi_desc, &pdev->dev, MSI_DESC_ASSOCIATED) {
+		if (msi_desc->msi_index == msix_idx)
+			break;
+	}
+
+	if (!msi_desc) {
+		err = -ENXIO;
+		goto err_out;
+	}
+
+	/* Get the vector control register (offset 0xc) pointed by msix_idx */
+	vec_ctrl = pdev->msix_base + msix_idx * PCI_MSIX_ENTRY_SIZE;
+	vec_ctrl += PCI_MSIX_ENTRY_VECTOR_CTRL;
+
+	val = readl(vec_ctrl);
+	val &= ~PCI_MSIX_ENTRY_CTRL_ST;
+	val |= FIELD_PREP(PCI_MSIX_ENTRY_CTRL_ST, tag);
+	writel(val, vec_ctrl);
+
+	/* Read back to flush the update */
+	val = readl(vec_ctrl);
+
+err_out:
+	msi_unlock_descs(&pdev->dev);
+	return err;
+#else
+	return -ENODEV;
+#endif
+}
+
+/* Write tag to ST table - Return 0 if OK, otherwise -errno */
+static int write_tag_to_st_table(struct pci_dev *pdev, int index, u16 tag)
+{
+	int st_table_size;
+	int offset;
+
+	/* Check if index is out of bound */
+	st_table_size = get_st_table_size(pdev);
+	if (index >= st_table_size)
+		return -ENXIO;
+
+	offset = pdev->tph_cap + PCI_TPH_BASE_SIZEOF + index * sizeof(u16);
+
+	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
+ *
+ * Return the Steering Tag for a target memory that is associated with a
+ * specific CPU as indicated by cpu_uid.
+ *
+ * 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)
+{
+#ifdef CONFIG_ACPI
+	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;
+#else
+	return -ENODEV;
+#endif
+}
+EXPORT_SYMBOL(pcie_tph_get_cpu_st);
+
+/**
+ * pcie_tph_set_st_entry() - Set Steering Tag in the ST table entry
+ * @pdev: PCI device
+ * @index: ST table entry index
+ * @tag: Steering Tag to be written
+ *
+ * Figure out the proper location of ST table, either in the MSI-X table or
+ * in the TPH Extended Capability space, and write the Steering Tag into
+ * the ST entry pointed by index.
+ *
+ * Return: 0 if success, otherwise negative value (-errno)
+ */
+int pcie_tph_set_st_entry(struct pci_dev *pdev, unsigned int index, u16 tag)
+{
+	u32 loc;
+	int err = 0;
+
+	if (!pdev->tph_cap)
+		return -EINVAL;
+
+	if (!pdev->tph_enabled)
+		return -EINVAL;
+
+	/* No need to write tag if device is in "No ST Mode" */
+	if (pdev->tph_mode == PCI_TPH_ST_NS_MODE)
+		return 0;
+
+	/*
+	 * Disable TPH before updating ST to avoid potential instability as
+	 * cautioned in PCIe r6.2, sec 6.17.3, "ST Modes of Operation"
+	 */
+	set_ctrl_reg_req_en(pdev, PCI_TPH_REQ_DISABLE);
+
+	loc = get_st_table_loc(pdev);
+	/* Convert loc to match with PCI_TPH_LOC_* */
+	loc = FIELD_PREP(PCI_TPH_CAP_LOC_MASK, loc);
+
+	switch (loc) {
+	case PCI_TPH_LOC_MSIX:
+		err = write_tag_to_msix(pdev, index, tag);
+		break;
+	case PCI_TPH_LOC_CAP:
+		err = write_tag_to_st_table(pdev, index, tag);
+		break;
+	default:
+		err = -EINVAL;
+	}
+
+	if (err) {
+		pcie_disable_tph(pdev);
+		return err;
+	}
+
+	set_ctrl_reg_req_en(pdev, pdev->tph_mode);
+
+	pci_dbg(pdev, "set steering tag: %s table, index=%d, tag=%#04x\n",
+		(loc == PCI_TPH_LOC_MSIX) ? "MSI-X" : "ST", index, tag);
+
+	return 0;
+}
+EXPORT_SYMBOL(pcie_tph_set_st_entry);
 
 /**
  * pcie_disable_tph - Turn off TPH support for device
···
 void pci_restore_tph_state(struct pci_dev *pdev)
 {
 	struct pci_cap_saved_state *save_state;
+	int num_entries, i, offset;
+	u16 *st_entry;
 	u32 *cap;
 
 	if (!pdev->tph_cap)
···
 	/* Restore control register and all ST entries */
 	cap = &save_state->cap.data[0];
 	pci_write_config_dword(pdev, pdev->tph_cap + PCI_TPH_CTRL, *cap++);
+	st_entry = (u16 *)cap;
+	offset = PCI_TPH_BASE_SIZEOF;
+	num_entries = get_st_table_size(pdev);
+	for (i = 0; i < num_entries; i++) {
+		pci_write_config_word(pdev, pdev->tph_cap + offset,
+				      *st_entry++);
+		offset += sizeof(u16);
+	}
 }
 
 void pci_save_tph_state(struct pci_dev *pdev)
 {
 	struct pci_cap_saved_state *save_state;
+	int num_entries, i, offset;
+	u16 *st_entry;
 	u32 *cap;
 
 	if (!pdev->tph_cap)
···
 	/* Save control register */
 	cap = &save_state->cap.data[0];
 	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CTRL, cap++);
+
+	/* Save all ST entries in extended capability structure */
+	st_entry = (u16 *)cap;
+	offset = PCI_TPH_BASE_SIZEOF;
+	num_entries = get_st_table_size(pdev);
+	for (i = 0; i < num_entries; i++) {
+		pci_read_config_word(pdev, pdev->tph_cap + offset,
+				     st_entry++);
+		offset += sizeof(u16);
+	}
 }
 
 void pci_no_tph(void)
···
 
 void pci_tph_init(struct pci_dev *pdev)
 {
+	int num_entries;
 	u32 save_size;
 
 	pdev->tph_cap = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_TPH);
 	if (!pdev->tph_cap)
 		return;
 
-	save_size = sizeof(u32);
+	num_entries = get_st_table_size(pdev);
+	save_size = sizeof(u32) + num_entries * sizeof(u16);
 	pci_add_ext_cap_save_buffer(pdev, PCI_EXT_CAP_ID_TPH, save_size);
 }

include/linux/pci-tph.h

···
 #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);
 void pcie_disable_tph(struct pci_dev *pdev);
 int pcie_enable_tph(struct pci_dev *pdev, int mode);
 #else
+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 void pcie_disable_tph(struct pci_dev *pdev) { }
 static inline int pcie_enable_tph(struct pci_dev *pdev, int mode)
 { return -EINVAL; }