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); 147