PCI: Add PTM clock granularity information

The PTM Control register (PCIe r3.1, sec 7.32.3) contains an Effective
Granularity field:

  This provides information relating to the expected accuracy of the PTM
  clock, but does not otherwise affect the PTM mechanism.

Set the Effective Granularity based on the PTM Root and any intervening PTM
Time Sources.

This does not set Effective Granularity for Root Complex Integrated
Endpoints because I don't know how to figure out clock granularity for
them.  The spec says:

  ... system software must set [Effective Granularity] to the value
  reported in the Local Clock Granularity field by the associated PTM
  Time Source.

but I don't know how to identify the associated PTM Time Source.  Normally
it's the upstream bridge, but an integrated endpoint has no upstream
bridge.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pcie/ptm.c

@@ -19,13 +19,29 @@
 
 static void pci_ptm_info(struct pci_dev *dev)
 {
-	dev_info(&dev->dev, "PTM enabled%s\n", dev->ptm_root ? " (root)" : "");
+	char clock_desc[8];
+
+	switch (dev->ptm_granularity) {
+	case 0:
+		snprintf(clock_desc, sizeof(clock_desc), "unknown");
+		break;
+	case 255:
+		snprintf(clock_desc, sizeof(clock_desc), ">254ns");
+		break;
+	default:
+		snprintf(clock_desc, sizeof(clock_desc), "%udns",
+			 dev->ptm_granularity);
+		break;
+	}
+	dev_info(&dev->dev, "PTM enabled%s, %s granularity\n",
+		 dev->ptm_root ? " (root)" : "", clock_desc);
 }
 
 void pci_ptm_init(struct pci_dev *dev)
 {
 	int pos;
 	u32 cap, ctrl;
+	u8 local_clock;
 	struct pci_dev *ups;
 
 	if (!pci_is_pcie(dev))
@@ -45,6 +61,7 @@ void pci_ptm_init(struct pci_dev *dev)
 		return;
 
 	pci_read_config_dword(dev, pos + PCI_PTM_CAP, &cap);
+	local_clock = (cap & PCI_PTM_GRANULARITY_MASK) >> 8;
 
 	/*
 	 * There's no point in enabling PTM unless it's enabled in the
@@ -55,14 +72,20 @@ void pci_ptm_init(struct pci_dev *dev)
 	ups = pci_upstream_bridge(dev);
 	if (ups && ups->ptm_enabled) {
 		ctrl = PCI_PTM_CTRL_ENABLE;
+		if (ups->ptm_granularity == 0)
+			dev->ptm_granularity = 0;
+		else if (ups->ptm_granularity > local_clock)
+			dev->ptm_granularity = ups->ptm_granularity;
 	} else {
 		if (cap & PCI_PTM_CAP_ROOT) {
 			ctrl = PCI_PTM_CTRL_ENABLE | PCI_PTM_CTRL_ROOT;
 			dev->ptm_root = 1;
+			dev->ptm_granularity = local_clock;
 		} else
 			return;
 	}
 
+	ctrl |= dev->ptm_granularity << 8;
 	pci_write_config_dword(dev, pos + PCI_PTM_CTRL, ctrl);
 	dev->ptm_enabled = 1;
 
@@ -98,18 +121,22 @@ int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
 		ups = pci_upstream_bridge(dev);
 		if (!ups || !ups->ptm_enabled)
 			return -EINVAL;
+
+		dev->ptm_granularity = ups->ptm_granularity;
 	} else if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
+		dev->ptm_granularity = 0;
 	} else
 		return -EINVAL;
 
 	ctrl = PCI_PTM_CTRL_ENABLE;
+	ctrl |= dev->ptm_granularity << 8;
 	pci_write_config_dword(dev, pos + PCI_PTM_CTRL, ctrl);
 	dev->ptm_enabled = 1;
 
 	pci_ptm_info(dev);
 
 	if (granularity)
-		*granularity = 0;
+		*granularity = dev->ptm_granularity;
 	return 0;
 }
 EXPORT_SYMBOL(pci_enable_ptm);

include/linux/pci.h

@@ -371,6 +371,7 @@ struct pci_dev {
 #ifdef CONFIG_PCIE_PTM
 	unsigned int	ptm_root:1;
 	unsigned int	ptm_enabled:1;
+	u8		ptm_granularity;
 #endif
 #ifdef CONFIG_PCI_MSI
 	const struct attribute_group **msi_irq_groups;

include/uapi/linux/pci_regs.h

@@ -969,6 +969,7 @@
 #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_GRANULARITY_MASK	0x0000FF00  /* Clock granularity */
 #define PCI_PTM_CTRL			0x08	    /* PTM Control */
 #define  PCI_PTM_CTRL_ENABLE		0x00000001  /* PTM enable */
 #define  PCI_PTM_CTRL_ROOT		0x00000002  /* Root select */