[PATCH V4 03/12] PCI/TPH: Add pcie_tph_modes() to query TPH modes

[Wei Huang <wei.huang2@xxxxxxx>]

Add pcie_tph_modes() to allow drivers to query the TPH modes supported
by an endpoint device, as reported in the TPH Requester Capability
register. The modes are reported as a bitmask and current supported
modes include:

 - PCI_TPH_CAP_NO_ST: NO ST Mode Supported
 - PCI_TPH_CAP_INT_VEC: Interrupt Vector Mode Supported
 - PCI_TPH_CAP_DEV_SPEC: Device Specific Mode Supported

Co-developed-by: Eric Van Tassell <Eric.VanTassell@xxxxxxx>
Signed-off-by: Eric Van Tassell <Eric.VanTassell@xxxxxxx>
Signed-off-by: Wei Huang <wei.huang2@xxxxxxx>
Reviewed-by: Ajit Khaparde <ajit.khaparde@xxxxxxxxxxxx>
Reviewed-by: Somnath Kotur <somnath.kotur@xxxxxxxxxxxx>
Reviewed-by: Andy Gospodarek <andrew.gospodarek@xxxxxxxxxxxx>
---
 drivers/pci/pcie/tph.c  | 33 +++++++++++++++++++++++++++++++++
 include/linux/pci-tph.h | 18 ++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 include/linux/pci-tph.h

diff --git a/drivers/pci/pcie/tph.c b/drivers/pci/pcie/tph.c
index a547858c3f68..a28dced3097d 100644
--- a/drivers/pci/pcie/tph.c
+++ b/drivers/pci/pcie/tph.c
@@ -6,9 +6,42 @@
  *     Eric Van Tassell <Eric.VanTassell@xxxxxxx>
  *     Wei Huang <wei.huang2@xxxxxxx>
  */
+#include <linux/pci.h>
+#include <linux/pci-tph.h>
 
 #include "../pci.h"
 
+static u8 get_st_modes(struct pci_dev *pdev)
+{
+	u32 reg;
+
+	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CAP, &reg);
+	reg &= PCI_TPH_CAP_NO_ST | PCI_TPH_CAP_INT_VEC | PCI_TPH_CAP_DEV_SPEC;
+
+	return reg;
+}
+
+/**
+ * pcie_tph_modes - Get the ST modes supported by device
+ * @pdev: PCI device
+ *
+ * Returns a bitmask with all TPH modes supported by a device as shown in the
+ * TPH capability register. Current supported modes include:
+ *   PCI_TPH_CAP_NO_ST - NO ST Mode Supported
+ *   PCI_TPH_CAP_INT_VEC - Interrupt Vector Mode Supported
+ *   PCI_TPH_CAP_DEV_SPEC - Device Specific Mode Supported
+ *
+ * Return: 0 when TPH is not supported, otherwise bitmask of supported modes
+ */
+int pcie_tph_modes(struct pci_dev *pdev)
+{
+	if (!pdev->tph_cap)
+		return 0;
+
+	return get_st_modes(pdev);
+}
+EXPORT_SYMBOL(pcie_tph_modes);
+
 void pci_tph_init(struct pci_dev *pdev)
 {
 	pdev->tph_cap = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_TPH);
diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
new file mode 100644
index 000000000000..fa378afe9c7e
--- /dev/null
+++ b/include/linux/pci-tph.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * TPH (TLP Processing Hints)
+ *
+ * Copyright (C) 2024 Advanced Micro Devices, Inc.
+ *     Eric Van Tassell <Eric.VanTassell@xxxxxxx>
+ *     Wei Huang <wei.huang2@xxxxxxx>
+ */
+#ifndef LINUX_PCI_TPH_H
+#define LINUX_PCI_TPH_H
+
+#ifdef CONFIG_PCIE_TPH
+int pcie_tph_modes(struct pci_dev *pdev);
+#else
+static inline int pcie_tph_modes(struct pci_dev *pdev) { return 0; }
+#endif
+
+#endif /* LINUX_PCI_TPH_H */
-- 
2.45.1