PCI: Add pci_enable_ptm() for drivers to enable PTM on endpoints

Add an pci_enable_ptm() interface so drivers can enable PTM.

The PCI core enables PTM on PTM Roots and switches automatically, but we
don't enable PTM on endpoints unless a driver requests it.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pcie/ptm.c

@@ -68,3 +68,48 @@ void pci_ptm_init(struct pci_dev *dev)
 
 	pci_ptm_info(dev);
 }
+
+int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
+{
+	int pos;
+	u32 cap, ctrl;
+	struct pci_dev *ups;
+
+	if (!pci_is_pcie(dev))
+		return -EINVAL;
+
+	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_PTM);
+	if (!pos)
+		return -EINVAL;
+
+	pci_read_config_dword(dev, pos + PCI_PTM_CAP, &cap);
+	if (!(cap & PCI_PTM_CAP_REQ))
+		return -EINVAL;
+
+	/*
+	 * For a PCIe Endpoint, PTM is only useful if the endpoint can
+	 * issue PTM requests to upstream devices that have PTM enabled.
+	 *
+	 * For Root Complex Integrated Endpoints, there is no upstream
+	 * device, so there must be some implementation-specific way to
+	 * associate the endpoint with a time source.
+	 */
+	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ENDPOINT) {
+		ups = pci_upstream_bridge(dev);
+		if (!ups || !ups->ptm_enabled)
+			return -EINVAL;
+	} else if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
+	} else
+		return -EINVAL;
+
+	ctrl = PCI_PTM_CTRL_ENABLE;
+	pci_write_config_dword(dev, pos + PCI_PTM_CTRL, ctrl);
+	dev->ptm_enabled = 1;
+
+	pci_ptm_info(dev);
+
+	if (granularity)
+		*granularity = 0;
+	return 0;
+}
+EXPORT_SYMBOL(pci_enable_ptm);

include/linux/pci.h

@@ -1407,6 +1407,13 @@ static inline void pci_disable_ats(struct pci_dev *d) { }
 static inline int pci_ats_queue_depth(struct pci_dev *d) { return -ENODEV; }
 #endif
 
+#ifdef CONFIG_PCIE_PTM
+int pci_enable_ptm(struct pci_dev *dev, u8 *granularity);
+#else
+static inline int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
+{ return -EINVAL; }
+#endif
+
 void pci_cfg_access_lock(struct pci_dev *dev);
 bool pci_cfg_access_trylock(struct pci_dev *dev);
 void pci_cfg_access_unlock(struct pci_dev *dev);

include/uapi/linux/pci_regs.h

@@ -967,6 +967,7 @@
 
 /* Precision Time Measurement */
 #define PCI_PTM_CAP			0x04	    /* PTM Capability */
+#define  PCI_PTM_CAP_REQ		0x00000001  /* Requester capable */
 #define  PCI_PTM_CAP_ROOT		0x00000004  /* Root capable */
 #define PCI_PTM_CTRL			0x08	    /* PTM Control */
 #define  PCI_PTM_CTRL_ENABLE		0x00000001  /* PTM enable */