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From: Wei Huang <wei.huang2@amd.com>
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	<linux-doc@vger.kernel.org>, <netdev@vger.kernel.org>
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Subject: [PATCH V2 6/9] PCI/TPH: Retrieve steering tag from ACPI _DSM
Date: Fri, 31 May 2024 16:38:38 -0500
Message-ID: <20240531213841.3246055-7-wei.huang2@amd.com>
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According to PCI SIG ECN, calling the _DSM firmware method for a given
CPU_UID returns the steering tags for different types of memory
(volatile, non-volatile). These tags are supposed to be used in ST
table entry for optimal results.

Co-developed-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com> 
Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
---
 drivers/pci/pcie/tph.c  | 103 +++++++++++++++++++++++++++++++++++++++-
 include/linux/pci-tph.h |  34 +++++++++++++
 2 files changed, 136 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/tph.c b/drivers/pci/pcie/tph.c
index 320b99c60365..425935a14b62 100644
--- a/drivers/pci/pcie/tph.c
+++ b/drivers/pci/pcie/tph.c
@@ -158,6 +158,98 @@ static int tph_get_table_location(struct pci_dev *dev, u8 *loc_out)
 	return 0;
 }
 
+static u16 tph_extract_tag(enum tph_mem_type mem_type, u8 req_type,
+			   union st_info *st_tag)
+{
+	switch (req_type) {
+	case PCI_TPH_REQ_TPH_ONLY: /* 8 bit tags */
+		switch (mem_type) {
+		case TPH_MEM_TYPE_VM:
+			if (st_tag->vm_st_valid)
+				return st_tag->vm_st;
+			break;
+		case TPH_MEM_TYPE_PM:
+			if (st_tag->pm_st_valid)
+				return st_tag->pm_st;
+			break;
+		}
+		break;
+	case PCI_TPH_REQ_EXT_TPH: /* 16 bit tags */
+		switch (mem_type) {
+		case TPH_MEM_TYPE_VM:
+			if (st_tag->vm_xst_valid)
+				return st_tag->vm_xst;
+			break;
+		case TPH_MEM_TYPE_PM:
+			if (st_tag->pm_xst_valid)
+				return st_tag->pm_xst;
+			break;
+		}
+		break;
+	default:
+		pr_err("invalid steering tag in ACPI _DSM\n");
+		return 0;
+	}
+
+	return 0;
+}
+
+#define MIN_ST_DSM_REV		7
+#define ST_DSM_FUNC_INDEX	0xf
+static bool invoke_dsm(acpi_handle handle, u32 cpu_uid, u8 ph,
+		       u8 target_type, bool cache_ref_valid,
+		       u64 cache_ref, union st_info *st_out)
+{
+	union acpi_object in_obj, in_buf[3], *out_obj;
+
+	in_buf[0].integer.type = ACPI_TYPE_INTEGER;
+	in_buf[0].integer.value = 0; /* 0 => processor cache steering tags */
+
+	in_buf[1].integer.type = ACPI_TYPE_INTEGER;
+	in_buf[1].integer.value = cpu_uid;
+
+	in_buf[2].integer.type = ACPI_TYPE_INTEGER;
+	in_buf[2].integer.value = ph & 3;
+	in_buf[2].integer.value |= (target_type & 1) << 2;
+	in_buf[2].integer.value |= (cache_ref_valid & 1) << 3;
+	in_buf[2].integer.value |= (cache_ref << 32);
+
+	in_obj.type = ACPI_TYPE_PACKAGE;
+	in_obj.package.count = ARRAY_SIZE(in_buf);
+	in_obj.package.elements = in_buf;
+
+	out_obj = acpi_evaluate_dsm(handle, &pci_acpi_dsm_guid, MIN_ST_DSM_REV,
+				    ST_DSM_FUNC_INDEX, &in_obj);
+
+	if (!out_obj)
+		return false;
+
+	if (out_obj->type != ACPI_TYPE_BUFFER) {
+		pr_err("invalid return type %d from TPH _DSM\n",
+		       out_obj->type);
+		ACPI_FREE(out_obj);
+		return false;
+	}
+
+	st_out->value = *((u64 *)(out_obj->buffer.pointer));
+
+	ACPI_FREE(out_obj);
+
+	return true;
+}
+
+static acpi_handle root_complex_acpi_handle(struct pci_dev *dev)
+{
+	struct pci_dev *root_port;
+
+	root_port = pcie_find_root_port(dev);
+
+	if (!root_port || !root_port->bus || !root_port->bus->bridge)
+		return NULL;
+
+	return ACPI_HANDLE(root_port->bus->bridge);
+}
+
 static bool msix_nr_in_bounds(struct pci_dev *dev, int msix_nr)
 {
 	u16 tbl_sz;
@@ -441,7 +533,16 @@ bool pcie_tph_get_st(struct pci_dev *dev, unsigned int cpu,
 		    enum tph_mem_type mem_type, u8 req_type,
 		    u16 *tag)
 {
-	*tag = 0;
+	union st_info info;
+
+	if (!invoke_dsm(root_complex_acpi_handle(dev), cpu, 0, 0, false, 0,
+			&info)) {
+		*tag = 0;
+		return false;
+	}
+
+	*tag = tph_extract_tag(mem_type, req_type, &info);
+	pr_debug("%s: cpu=%d tag=%d\n", __func__, cpu, *tag);
 
 	return true;
 }
diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
index 4fbd1e2fd98c..79533c6254c2 100644
--- a/include/linux/pci-tph.h
+++ b/include/linux/pci-tph.h
@@ -14,6 +14,40 @@ enum tph_mem_type {
 	TPH_MEM_TYPE_PM		/* persistent memory type */
 };
 
+/*
+ * The st_info struct defines the steering tag returned by the firmware _DSM
+ * method defined in PCI SIG ECN. The specification is available at:
+ * https://members.pcisig.com/wg/PCI-SIG/document/15470.
+
+ * @vm_st_valid:  8 bit tag for volatile memory is valid
+ * @vm_xst_valid: 16 bit tag for volatile memory is valid
+ * @vm_ignore:    1 => was and will be ignored, 0 => ph should be supplied
+ * @vm_st:        8 bit steering tag for volatile mem
+ * @vm_xst:       16 bit steering tag for volatile mem
+ * @pm_st_valid:  8 bit tag for persistent memory is valid
+ * @pm_xst_valid: 16 bit tag for persistent memory is valid
+ * @pm_ignore:    1 => was and will be ignore, 0 => ph should be supplied
+ * @pm_st:        8 bit steering tag for persistent mem
+ * @pm_xst:       16 bit steering tag for persistent mem
+ */
+union st_info {
+	struct {
+		u64 vm_st_valid:1,
+		vm_xst_valid:1,
+		vm_ph_ignore:1,
+		rsvd1:5,
+		vm_st:8,
+		vm_xst:16,
+		pm_st_valid:1,
+		pm_xst_valid:1,
+		pm_ph_ignore:1,
+		rsvd2:5,
+		pm_st:8,
+		pm_xst:16;
+	};
+	u64 value;
+};
+
 #ifdef CONFIG_PCIE_TPH
 int pcie_tph_disable(struct pci_dev *dev);
 int tph_set_dev_nostmode(struct pci_dev *dev);
-- 
2.44.0