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>

1 files changed, 29 insertions, 2 deletions

diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
index a14ac94b96dc..bab8ac63c4f3 100644
--- a/drivers/pci/pcie/ptm.c
+++ b/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);