1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Primary to Sideband (P2SB) bridge access support 4 * 5 * Copyright (c) 2017, 2021-2022 Intel Corporation. 6 * 7 * Authors: Andy Shevchenko <andriy.shevchenko@linux.intel.com> 8 * Jonathan Yong <jonathan.yong@intel.com> 9 */ 10 11 #include <linux/bits.h> 12 #include <linux/export.h> 13 #include <linux/pci.h> 14 #include <linux/platform_data/x86/p2sb.h> 15 16 #include <asm/cpu_device_id.h> 17 #include <asm/intel-family.h> 18 19 #define P2SBC 0xe0 20 #define P2SBC_HIDE BIT(8) 21 22 #define P2SB_DEVFN_DEFAULT PCI_DEVFN(31, 1) 23 24 static const struct x86_cpu_id p2sb_cpu_ids[] = { 25 X86_MATCH_INTEL_FAM6_MODEL(ATOM_GOLDMONT, PCI_DEVFN(13, 0)), 26 {} 27 }; 28 29 /* 30 * Cache BAR0 of P2SB device functions 0 to 7. 31 * TODO: The constant 8 is the number of functions that PCI specification 32 * defines. Same definitions exist tree-wide. Unify this definition and 33 * the other definitions then move to include/uapi/linux/pci.h. 34 */ 35 #define NR_P2SB_RES_CACHE 8 36 37 struct p2sb_res_cache { 38 u32 bus_dev_id; 39 struct resource res; 40 }; 41 42 static struct p2sb_res_cache p2sb_resources[NR_P2SB_RES_CACHE]; 43 44 static int p2sb_get_devfn(unsigned int *devfn) 45 { 46 unsigned int fn = P2SB_DEVFN_DEFAULT; 47 const struct x86_cpu_id *id; 48 49 id = x86_match_cpu(p2sb_cpu_ids); 50 if (id) 51 fn = (unsigned int)id->driver_data; 52 53 *devfn = fn; 54 return 0; 55 } 56 57 static bool p2sb_valid_resource(struct resource *res) 58 { 59 if (res->flags) 60 return true; 61 62 return false; 63 } 64 65 /* Copy resource from the first BAR of the device in question */ 66 static void p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem) 67 { 68 struct resource *bar0 = &pdev->resource[0]; 69 70 /* Make sure we have no dangling pointers in the output */ 71 memset(mem, 0, sizeof(*mem)); 72 73 /* 74 * We copy only selected fields from the original resource. 75 * Because a PCI device will be removed soon, we may not use 76 * any allocated data, hence we may not copy any pointers. 77 */ 78 mem->start = bar0->start; 79 mem->end = bar0->end; 80 mem->flags = bar0->flags; 81 mem->desc = bar0->desc; 82 } 83 84 static void p2sb_scan_and_cache_devfn(struct pci_bus *bus, unsigned int devfn) 85 { 86 struct p2sb_res_cache *cache = &p2sb_resources[PCI_FUNC(devfn)]; 87 struct pci_dev *pdev; 88 89 pdev = pci_scan_single_device(bus, devfn); 90 if (!pdev) 91 return; 92 93 p2sb_read_bar0(pdev, &cache->res); 94 cache->bus_dev_id = bus->dev.id; 95 96 pci_stop_and_remove_bus_device(pdev); 97 return; 98 } 99 100 static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn) 101 { 102 unsigned int slot, fn; 103 104 if (PCI_FUNC(devfn) == 0) { 105 /* 106 * When function number of the P2SB device is zero, scan it and 107 * other function numbers, and if devices are available, cache 108 * their BAR0s. 109 */ 110 slot = PCI_SLOT(devfn); 111 for (fn = 0; fn < NR_P2SB_RES_CACHE; fn++) 112 p2sb_scan_and_cache_devfn(bus, PCI_DEVFN(slot, fn)); 113 } else { 114 /* Scan the P2SB device and cache its BAR0 */ 115 p2sb_scan_and_cache_devfn(bus, devfn); 116 } 117 118 if (!p2sb_valid_resource(&p2sb_resources[PCI_FUNC(devfn)].res)) 119 return -ENOENT; 120 121 return 0; 122 } 123 124 static struct pci_bus *p2sb_get_bus(struct pci_bus *bus) 125 { 126 static struct pci_bus *p2sb_bus; 127 128 bus = bus ?: p2sb_bus; 129 if (bus) 130 return bus; 131 132 /* Assume P2SB is on the bus 0 in domain 0 */ 133 p2sb_bus = pci_find_bus(0, 0); 134 return p2sb_bus; 135 } 136 137 static int p2sb_cache_resources(void) 138 { 139 struct pci_bus *bus; 140 unsigned int devfn_p2sb; 141 u32 value = P2SBC_HIDE; 142 int ret; 143 144 /* Get devfn for P2SB device itself */ 145 ret = p2sb_get_devfn(&devfn_p2sb); 146 if (ret) 147 return ret; 148 149 bus = p2sb_get_bus(NULL); 150 if (!bus) 151 return -ENODEV; 152 153 /* 154 * Prevent concurrent PCI bus scan from seeing the P2SB device and 155 * removing via sysfs while it is temporarily exposed. 156 */ 157 pci_lock_rescan_remove(); 158 159 /* 160 * The BIOS prevents the P2SB device from being enumerated by the PCI 161 * subsystem, so we need to unhide and hide it back to lookup the BAR. 162 * Unhide the P2SB device here, if needed. 163 */ 164 pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value); 165 if (value & P2SBC_HIDE) 166 pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, 0); 167 168 ret = p2sb_scan_and_cache(bus, devfn_p2sb); 169 170 /* Hide the P2SB device, if it was hidden */ 171 if (value & P2SBC_HIDE) 172 pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, P2SBC_HIDE); 173 174 pci_unlock_rescan_remove(); 175 176 return ret; 177 } 178 179 /** 180 * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR 181 * @bus: PCI bus to communicate with 182 * @devfn: PCI slot and function to communicate with 183 * @mem: memory resource to be filled in 184 * 185 * If @bus is NULL, the bus 0 in domain 0 will be used. 186 * If @devfn is 0, it will be replaced by devfn of the P2SB device. 187 * 188 * Caller must provide a valid pointer to @mem. 189 * 190 * Return: 191 * 0 on success or appropriate errno value on error. 192 */ 193 int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) 194 { 195 struct p2sb_res_cache *cache; 196 int ret; 197 198 bus = p2sb_get_bus(bus); 199 if (!bus) 200 return -ENODEV; 201 202 if (!devfn) { 203 ret = p2sb_get_devfn(&devfn); 204 if (ret) 205 return ret; 206 } 207 208 cache = &p2sb_resources[PCI_FUNC(devfn)]; 209 if (cache->bus_dev_id != bus->dev.id) 210 return -ENODEV; 211 212 if (!p2sb_valid_resource(&cache->res)) 213 return -ENOENT; 214 215 memcpy(mem, &cache->res, sizeof(*mem)); 216 return 0; 217 } 218 EXPORT_SYMBOL_GPL(p2sb_bar); 219 220 static int __init p2sb_fs_init(void) 221 { 222 p2sb_cache_resources(); 223 return 0; 224 } 225 226 /* 227 * pci_rescan_remove_lock to avoid access to unhidden P2SB devices can 228 * not be locked in sysfs pci bus rescan path because of deadlock. To 229 * avoid the deadlock, access to P2SB devices with the lock at an early 230 * step in kernel initialization and cache required resources. This 231 * should happen after subsys_initcall which initializes PCI subsystem 232 * and before device_initcall which requires P2SB resources. 233 */ 234 fs_initcall(p2sb_fs_init); 235