PCI: Add TLP Processing Hints (TPH) support

Add support for PCIe TLP Processing Hints (TPH) support (see PCIe r6.2,
sec 6.17).

Add TPH register definitions in pci_regs.h, including the TPH Requester
capability register, TPH Requester control register, TPH Completer
capability, and the ST fields of MSI-X entry.

Introduce pcie_enable_tph() and pcie_disable_tph(), enabling drivers to
toggle TPH support and configure specific ST mode as needed. Also add a new
kernel parameter, "pci=notph", allowing users to disable TPH support across
the entire system.

Link: https://lore.kernel.org/r/20241002165954.128085-2-wei.huang2@amd.com
Co-developed-by: Jing Liu <jing2.liu@intel.com>
Co-developed-by: Paul Luse <paul.e.luse@linux.intel.com>
Co-developed-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Paul Luse <paul.e.luse@linux.intel.com>
Signed-off-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.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>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>

1 files changed, 197 insertions, 0 deletions

diff --git a/drivers/pci/tph.c b/drivers/pci/tph.c
new file mode 100644
index 000000000000..4d6317cbf8a6
--- /dev/null
+++ b/drivers/pci/tph.c
@@ -0,0 +1,197 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * TPH (TLP Processing Hints) support
+ *
+ * Copyright (C) 2024 Advanced Micro Devices, Inc.
+ *     Eric Van Tassell <Eric.VanTassell@amd.com>
+ *     Wei Huang <wei.huang2@amd.com>
+ */
+#include <linux/pci.h>
+#include <linux/bitfield.h>
+#include <linux/pci-tph.h>
+
+#include "pci.h"
+
+/* System-wide TPH disabled */
+static bool pci_tph_disabled;
+
+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_ST_NS | PCI_TPH_CAP_ST_IV | PCI_TPH_CAP_ST_DS;
+
+	return reg;
+}
+
+/* Return device's Root Port completer capability */
+static u8 get_rp_completer_type(struct pci_dev *pdev)
+{
+	struct pci_dev *rp;
+	u32 reg;
+	int ret;
+
+	rp = pcie_find_root_port(pdev);
+	if (!rp)
+		return 0;
+
+	ret = pcie_capability_read_dword(rp, PCI_EXP_DEVCAP2, &reg);
+	if (ret)
+		return 0;
+
+	return FIELD_GET(PCI_EXP_DEVCAP2_TPH_COMP_MASK, reg);
+}
+
+/**
+ * pcie_disable_tph - Turn off TPH support for device
+ * @pdev: PCI device
+ *
+ * Return: none
+ */
+void pcie_disable_tph(struct pci_dev *pdev)
+{
+	if (!pdev->tph_cap)
+		return;
+
+	if (!pdev->tph_enabled)
+		return;
+
+	pci_write_config_dword(pdev, pdev->tph_cap + PCI_TPH_CTRL, 0);
+
+	pdev->tph_mode = 0;
+	pdev->tph_req_type = 0;
+	pdev->tph_enabled = 0;
+}
+EXPORT_SYMBOL(pcie_disable_tph);
+
+/**
+ * pcie_enable_tph - Enable TPH support for device using a specific ST mode
+ * @pdev: PCI device
+ * @mode: ST mode to enable. Current supported modes include:
+ *
+ *   - PCI_TPH_ST_NS_MODE: NO ST Mode
+ *   - PCI_TPH_ST_IV_MODE: Interrupt Vector Mode
+ *   - PCI_TPH_ST_DS_MODE: Device Specific Mode
+ *
+ * Check whether the mode is actually supported by the device before enabling
+ * and return an error if not. Additionally determine what types of requests,
+ * TPH or extended TPH, can be issued by the device based on its TPH requester
+ * capability and the Root Port's completer capability.
+ *
+ * Return: 0 on success, otherwise negative value (-errno)
+ */
+int pcie_enable_tph(struct pci_dev *pdev, int mode)
+{
+	u32 reg;
+	u8 dev_modes;
+	u8 rp_req_type;
+
+	/* Honor "notph" kernel parameter */
+	if (pci_tph_disabled)
+		return -EINVAL;
+
+	if (!pdev->tph_cap)
+		return -EINVAL;
+
+	if (pdev->tph_enabled)
+		return -EBUSY;
+
+	/* Sanitize and check ST mode compatibility */
+	mode &= PCI_TPH_CTRL_MODE_SEL_MASK;
+	dev_modes = get_st_modes(pdev);
+	if (!((1 << mode) & dev_modes))
+		return -EINVAL;
+
+	pdev->tph_mode = mode;
+
+	/* Get req_type supported by device and its Root Port */
+	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CAP, &reg);
+	if (FIELD_GET(PCI_TPH_CAP_EXT_TPH, reg))
+		pdev->tph_req_type = PCI_TPH_REQ_EXT_TPH;
+	else
+		pdev->tph_req_type = PCI_TPH_REQ_TPH_ONLY;
+
+	rp_req_type = get_rp_completer_type(pdev);
+
+	/* Final req_type is the smallest value of two */
+	pdev->tph_req_type = min(pdev->tph_req_type, rp_req_type);
+
+	if (pdev->tph_req_type == PCI_TPH_REQ_DISABLE)
+		return -EINVAL;
+
+	/* Write them into TPH control register */
+	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CTRL, &reg);
+
+	reg &= ~PCI_TPH_CTRL_MODE_SEL_MASK;
+	reg |= FIELD_PREP(PCI_TPH_CTRL_MODE_SEL_MASK, pdev->tph_mode);
+
+	reg &= ~PCI_TPH_CTRL_REQ_EN_MASK;
+	reg |= FIELD_PREP(PCI_TPH_CTRL_REQ_EN_MASK, pdev->tph_req_type);
+
+	pci_write_config_dword(pdev, pdev->tph_cap + PCI_TPH_CTRL, reg);
+
+	pdev->tph_enabled = 1;
+
+	return 0;
+}
+EXPORT_SYMBOL(pcie_enable_tph);
+
+void pci_restore_tph_state(struct pci_dev *pdev)
+{
+	struct pci_cap_saved_state *save_state;
+	u32 *cap;
+
+	if (!pdev->tph_cap)
+		return;
+
+	if (!pdev->tph_enabled)
+		return;
+
+	save_state = pci_find_saved_ext_cap(pdev, PCI_EXT_CAP_ID_TPH);
+	if (!save_state)
+		return;
+
+	/* 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++);
+}
+
+void pci_save_tph_state(struct pci_dev *pdev)
+{
+	struct pci_cap_saved_state *save_state;
+	u32 *cap;
+
+	if (!pdev->tph_cap)
+		return;
+
+	if (!pdev->tph_enabled)
+		return;
+
+	save_state = pci_find_saved_ext_cap(pdev, PCI_EXT_CAP_ID_TPH);
+	if (!save_state)
+		return;
+
+	/* Save control register */
+	cap = &save_state->cap.data[0];
+	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CTRL, cap++);
+}
+
+void pci_no_tph(void)
+{
+	pci_tph_disabled = true;
+
+	pr_info("PCIe TPH is disabled\n");
+}
+
+void pci_tph_init(struct pci_dev *pdev)
+{
+	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);
+	pci_add_ext_cap_save_buffer(pdev, PCI_EXT_CAP_ID_TPH, save_size);
+}