[PATCH v8 2/7] PCI/TPH: Export pcie_tph_get_st_modes() for external use

[Chengwen Feng <fengchengwen@huawei.com>]

Export the helper to retrieve supported PCIe TPH steering tag modes so
that drivers like VFIO can query and expose device capabilities to
userspace.

Add stub functions for pcie_tph_get_st_table_size() and
pcie_tph_get_st_table_loc() when !CONFIG_PCIE_TPH.

Add tph_cap validation for pcie_tph_get_st_modes() and
pcie_tph_get_st_table_loc() to prevent invalid PCI configuration
space access when TPH is not supported.

Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/tph.c       | 19 +++++++++++++++++--
 include/linux/pci-tph.h |  7 +++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/tph.c b/drivers/pci/tph.c
index 877cf556242b..ba31b010f67a 100644
--- a/drivers/pci/tph.c
+++ b/drivers/pci/tph.c
@@ -145,15 +145,27 @@ static void set_ctrl_reg_req_en(struct pci_dev *pdev, u8 req_type)
 	pci_write_config_dword(pdev, pdev->tph_cap + PCI_TPH_CTRL, reg);
 }
 
-static u8 get_st_modes(struct pci_dev *pdev)
+/**
+ * pcie_tph_get_st_modes - Get supported Steering Tag modes
+ * @pdev: PCI device to query
+ *
+ * Return:
+ *  Bitmask of supported ST modes (PCI_TPH_CAP_ST_NS, PCI_TPH_CAP_ST_IV,
+ *                                 PCI_TPH_CAP_ST_DS)
+ */
+u8 pcie_tph_get_st_modes(struct pci_dev *pdev)
 {
 	u32 reg;
 
+	if (!pdev->tph_cap)
+		return 0;
+
 	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CAP, &reg);
 	reg &= PCI_TPH_CAP_ST_NS | PCI_TPH_CAP_ST_IV | PCI_TPH_CAP_ST_DS;
 
 	return reg;
 }
+EXPORT_SYMBOL(pcie_tph_get_st_modes);
 
 /**
  * pcie_tph_get_st_table_loc - Return the device's ST table location
@@ -168,6 +180,9 @@ u32 pcie_tph_get_st_table_loc(struct pci_dev *pdev)
 {
 	u32 reg;
 
+	if (!pdev->tph_cap)
+		return PCI_TPH_LOC_NONE;
+
 	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CAP, &reg);
 
 	return reg & PCI_TPH_CAP_LOC_MASK;
@@ -395,7 +410,7 @@ int pcie_enable_tph(struct pci_dev *pdev, int mode)
 
 	/* Sanitize and check ST mode compatibility */
 	mode &= PCI_TPH_CTRL_MODE_SEL_MASK;
-	dev_modes = get_st_modes(pdev);
+	dev_modes = pcie_tph_get_st_modes(pdev);
 	if (!((1 << mode) & dev_modes))
 		return -EINVAL;
 
diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
index be68cd17f2f8..5772d48ea444 100644
--- a/include/linux/pci-tph.h
+++ b/include/linux/pci-tph.h
@@ -30,6 +30,7 @@ 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);
 u32 pcie_tph_get_st_table_loc(struct pci_dev *pdev);
+u8 pcie_tph_get_st_modes(struct pci_dev *pdev);
 #else
 static inline int pcie_tph_set_st_entry(struct pci_dev *pdev,
 					unsigned int index, u16 tag)
@@ -41,6 +42,12 @@ static inline int pcie_tph_get_cpu_st(struct pci_dev *dev,
 static inline void pcie_disable_tph(struct pci_dev *pdev) { }
 static inline int pcie_enable_tph(struct pci_dev *pdev, int mode)
 { return -EINVAL; }
+static inline u16 pcie_tph_get_st_table_size(struct pci_dev *pdev)
+{ return 0; }
+static inline u32 pcie_tph_get_st_table_loc(struct pci_dev *pdev)
+{ return 0; }
+static inline u8 pcie_tph_get_st_modes(struct pci_dev *pdev)
+{ return 0; }
 #endif
 
 #endif /* LINUX_PCI_TPH_H */
-- 
2.17.1