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 = pci_resource_n(pdev, 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 } 98 99 static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn) 100 { 101 unsigned int slot, fn; 102 103 if (PCI_FUNC(devfn) == 0) { 104 /* 105 * When function number of the P2SB device is zero, scan it and 106 * other function numbers, and if devices are available, cache 107 * their BAR0s. 108 */ 109 slot = PCI_SLOT(devfn); 110 for (fn = 0; fn < NR_P2SB_RES_CACHE; fn++) 111 p2sb_scan_and_cache_devfn(bus, PCI_DEVFN(slot, fn)); 112 } else { 113 /* Scan the P2SB device and cache its BAR0 */ 114 p2sb_scan_and_cache_devfn(bus, devfn); 115 } 116 117 if (!p2sb_valid_resource(&p2sb_resources[PCI_FUNC(devfn)].res)) 118 return -ENOENT; 119 120 return 0; 121 } 122 123 static struct pci_bus *p2sb_get_bus(struct pci_bus *bus) 124 { 125 static struct pci_bus *p2sb_bus; 126 127 bus = bus ?: p2sb_bus; 128 if (bus) 129 return bus; 130 131 /* Assume P2SB is on the bus 0 in domain 0 */ 132 p2sb_bus = pci_find_bus(0, 0); 133 return p2sb_bus; 134 } 135 136 static int p2sb_cache_resources(void) 137 { 138 unsigned int devfn_p2sb; 139 u32 value = P2SBC_HIDE; 140 struct pci_bus *bus; 141 u16 class; 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 * When a device with same devfn exists and its device class is not 155 * PCI_CLASS_MEMORY_OTHER for P2SB, do not touch it. 156 */ 157 pci_bus_read_config_word(bus, devfn_p2sb, PCI_CLASS_DEVICE, &class); 158 if (!PCI_POSSIBLE_ERROR(class) && class != PCI_CLASS_MEMORY_OTHER) 159 return -ENODEV; 160 161 /* 162 * Prevent concurrent PCI bus scan from seeing the P2SB device and 163 * removing via sysfs while it is temporarily exposed. 164 */ 165 pci_lock_rescan_remove(); 166 167 /* 168 * The BIOS prevents the P2SB device from being enumerated by the PCI 169 * subsystem, so we need to unhide and hide it back to lookup the BAR. 170 * Unhide the P2SB device here, if needed. 171 */ 172 pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value); 173 if (value & P2SBC_HIDE) 174 pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, 0); 175 176 ret = p2sb_scan_and_cache(bus, devfn_p2sb); 177 178 /* Hide the P2SB device, if it was hidden */ 179 if (value & P2SBC_HIDE) 180 pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, P2SBC_HIDE); 181 182 pci_unlock_rescan_remove(); 183 184 return ret; 185 } 186 187 /** 188 * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR 189 * @bus: PCI bus to communicate with 190 * @devfn: PCI slot and function to communicate with 191 * @mem: memory resource to be filled in 192 * 193 * If @bus is NULL, the bus 0 in domain 0 will be used. 194 * If @devfn is 0, it will be replaced by devfn of the P2SB device. 195 * 196 * Caller must provide a valid pointer to @mem. 197 * 198 * Return: 199 * 0 on success or appropriate errno value on error. 200 */ 201 int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) 202 { 203 struct p2sb_res_cache *cache; 204 int ret; 205 206 bus = p2sb_get_bus(bus); 207 if (!bus) 208 return -ENODEV; 209 210 if (!devfn) { 211 ret = p2sb_get_devfn(&devfn); 212 if (ret) 213 return ret; 214 } 215 216 cache = &p2sb_resources[PCI_FUNC(devfn)]; 217 if (cache->bus_dev_id != bus->dev.id) 218 return -ENODEV; 219 220 if (!p2sb_valid_resource(&cache->res)) 221 return -ENOENT; 222 223 memcpy(mem, &cache->res, sizeof(*mem)); 224 return 0; 225 } 226 EXPORT_SYMBOL_GPL(p2sb_bar); 227 228 static int __init p2sb_fs_init(void) 229 { 230 p2sb_cache_resources(); 231 return 0; 232 } 233 234 /* 235 * pci_rescan_remove_lock to avoid access to unhidden P2SB devices can 236 * not be locked in sysfs pci bus rescan path because of deadlock. To 237 * avoid the deadlock, access to P2SB devices with the lock at an early 238 * step in kernel initialization and cache required resources. This 239 * should happen after subsys_initcall which initializes PCI subsystem 240 * and before device_initcall which requires P2SB resources. 241 */ 242 fs_initcall(p2sb_fs_init); 243