drivers/pci/pcie/ptm.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * PCI Express Precision Time Measurement
   4  * Copyright (c) 2016, Intel Corporation.
   5  */
   6
   7 #include <linux/module.h>
   8 #include <linux/init.h>
   9 #include <linux/pci.h>
  10 #include "../pci.h"
  11
  12 static void pci_ptm_info(struct pci_dev *dev)
  13 {
  14         char clock_desc[8];
  15
  16         switch (dev->ptm_granularity) {
  17         case 0:
  18                 snprintf(clock_desc, sizeof(clock_desc), "unknown");
  19                 break;
  20         case 255:
  21                 snprintf(clock_desc, sizeof(clock_desc), ">254ns");
  22                 break;
  23         default:
  24                 snprintf(clock_desc, sizeof(clock_desc), "%uns",
  25                          dev->ptm_granularity);
  26                 break;
  27         }
  28         pci_info(dev, "PTM enabled%s, %s granularity\n",
  29                  dev->ptm_root ? " (root)" : "", clock_desc);
  30 }
  31
  32 void pci_ptm_init(struct pci_dev *dev)
  33 {
  34         int pos;
  35         u32 cap, ctrl;
  36         u8 local_clock;
  37         struct pci_dev *ups;
  38
  39         if (!pci_is_pcie(dev))
  40                 return;
  41
  42         /*
  43          * Enable PTM only on interior devices (root ports, switch ports,
  44          * etc.) on the assumption that it causes no link traffic until an
  45          * endpoint enables it.
  46          */
  47         if ((pci_pcie_type(dev) == PCI_EXP_TYPE_ENDPOINT ||
  48              pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END))
  49                 return;
  50
  51         /*
  52          * Switch Downstream Ports are not permitted to have a PTM
  53          * capability; their PTM behavior is controlled by the Upstream
  54          * Port (PCIe r5.0, sec 7.9.16).
  55          */
  56         ups = pci_upstream_bridge(dev);
  57         if (pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM &&
  58             ups && ups->ptm_enabled) {
  59                 dev->ptm_granularity = ups->ptm_granularity;
  60                 dev->ptm_enabled = 1;
  61                 return;
  62         }
  63
  64         pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_PTM);
  65         if (!pos)
  66                 return;
  67
  68         pci_read_config_dword(dev, pos + PCI_PTM_CAP, &cap);
  69         local_clock = (cap & PCI_PTM_GRANULARITY_MASK) >> 8;
  70
  71         /*
  72          * There's no point in enabling PTM unless it's enabled in the
  73          * upstream device or this device can be a PTM Root itself.  Per
  74          * the spec recommendation (PCIe r3.1, sec 7.32.3), select the
  75          * furthest upstream Time Source as the PTM Root.
  76          */
  77         if (ups && ups->ptm_enabled) {
  78                 ctrl = PCI_PTM_CTRL_ENABLE;
  79                 if (ups->ptm_granularity == 0)
  80                         dev->ptm_granularity = 0;
  81                 else if (ups->ptm_granularity > local_clock)
  82                         dev->ptm_granularity = ups->ptm_granularity;
  83         } else {
  84                 if (cap & PCI_PTM_CAP_ROOT) {
  85                         ctrl = PCI_PTM_CTRL_ENABLE | PCI_PTM_CTRL_ROOT;
  86                         dev->ptm_root = 1;
  87                         dev->ptm_granularity = local_clock;
  88                 } else
  89                         return;
  90         }
  91
  92         ctrl |= dev->ptm_granularity << 8;
  93         pci_write_config_dword(dev, pos + PCI_PTM_CTRL, ctrl);
  94         dev->ptm_enabled = 1;
  95
  96         pci_ptm_info(dev);
  97 }
  98
  99 int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
 100 {
 101         int pos;
 102         u32 cap, ctrl;
 103         struct pci_dev *ups;
 104
 105         if (!pci_is_pcie(dev))
 106                 return -EINVAL;
 107
 108         pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_PTM);
 109         if (!pos)
 110                 return -EINVAL;
 111
 112         pci_read_config_dword(dev, pos + PCI_PTM_CAP, &cap);
 113         if (!(cap & PCI_PTM_CAP_REQ))
 114                 return -EINVAL;
 115
 116         /*
 117          * For a PCIe Endpoint, PTM is only useful if the endpoint can
 118          * issue PTM requests to upstream devices that have PTM enabled.
 119          *
 120          * For Root Complex Integrated Endpoints, there is no upstream
 121          * device, so there must be some implementation-specific way to
 122          * associate the endpoint with a time source.
 123          */
 124         if (pci_pcie_type(dev) == PCI_EXP_TYPE_ENDPOINT) {
 125                 ups = pci_upstream_bridge(dev);
 126                 if (!ups || !ups->ptm_enabled)
 127                         return -EINVAL;
 128
 129                 dev->ptm_granularity = ups->ptm_granularity;
 130         } else if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
 131                 dev->ptm_granularity = 0;
 132         } else
 133                 return -EINVAL;
 134
 135         ctrl = PCI_PTM_CTRL_ENABLE;
 136         ctrl |= dev->ptm_granularity << 8;
 137         pci_write_config_dword(dev, pos + PCI_PTM_CTRL, ctrl);
 138         dev->ptm_enabled = 1;
 139
 140         pci_ptm_info(dev);
 141
 142         if (granularity)
 143                 *granularity = dev->ptm_granularity;
 144         return 0;
 145 }
 146 EXPORT_SYMBOL(pci_enable_ptm);