arch/mips/kernel/mips-cm.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2013 Imagination Technologies
   4  * Author: Paul Burton <paul.burton@mips.com>
   5  */
   6
   7 #include <linux/errno.h>
   8 #include <linux/percpu.h>
   9 #include <linux/spinlock.h>
  10
  11 #include <asm/mips-cps.h>
  12 #include <asm/mipsregs.h>
  13
  14 void __iomem *mips_gcr_base;
  15 void __iomem *mips_cm_l2sync_base;
  16 int mips_cm_is64;
  17
  18 static char *cm2_tr[8] = {
  19         "mem",  "gcr",  "gic",  "mmio",
  20         "0x04", "cpc", "0x06", "0x07"
  21 };
  22
  23 /* CM3 Tag ECC transaction type */
  24 static char *cm3_tr[16] = {
  25         [0x0] = "ReqNoData",
  26         [0x1] = "0x1",
  27         [0x2] = "ReqWData",
  28         [0x3] = "0x3",
  29         [0x4] = "IReqNoResp",
  30         [0x5] = "IReqWResp",
  31         [0x6] = "IReqNoRespDat",
  32         [0x7] = "IReqWRespDat",
  33         [0x8] = "RespNoData",
  34         [0x9] = "RespDataFol",
  35         [0xa] = "RespWData",
  36         [0xb] = "RespDataOnly",
  37         [0xc] = "IRespNoData",
  38         [0xd] = "IRespDataFol",
  39         [0xe] = "IRespWData",
  40         [0xf] = "IRespDataOnly"
  41 };
  42
  43 static char *cm2_cmd[32] = {
  44         [0x00] = "0x00",
  45         [0x01] = "Legacy Write",
  46         [0x02] = "Legacy Read",
  47         [0x03] = "0x03",
  48         [0x04] = "0x04",
  49         [0x05] = "0x05",
  50         [0x06] = "0x06",
  51         [0x07] = "0x07",
  52         [0x08] = "Coherent Read Own",
  53         [0x09] = "Coherent Read Share",
  54         [0x0a] = "Coherent Read Discard",
  55         [0x0b] = "Coherent Ready Share Always",
  56         [0x0c] = "Coherent Upgrade",
  57         [0x0d] = "Coherent Writeback",
  58         [0x0e] = "0x0e",
  59         [0x0f] = "0x0f",
  60         [0x10] = "Coherent Copyback",
  61         [0x11] = "Coherent Copyback Invalidate",
  62         [0x12] = "Coherent Invalidate",
  63         [0x13] = "Coherent Write Invalidate",
  64         [0x14] = "Coherent Completion Sync",
  65         [0x15] = "0x15",
  66         [0x16] = "0x16",
  67         [0x17] = "0x17",
  68         [0x18] = "0x18",
  69         [0x19] = "0x19",
  70         [0x1a] = "0x1a",
  71         [0x1b] = "0x1b",
  72         [0x1c] = "0x1c",
  73         [0x1d] = "0x1d",
  74         [0x1e] = "0x1e",
  75         [0x1f] = "0x1f"
  76 };
  77
  78 /* CM3 Tag ECC command type */
  79 static char *cm3_cmd[16] = {
  80         [0x0] = "Legacy Read",
  81         [0x1] = "Legacy Write",
  82         [0x2] = "Coherent Read Own",
  83         [0x3] = "Coherent Read Share",
  84         [0x4] = "Coherent Read Discard",
  85         [0x5] = "Coherent Evicted",
  86         [0x6] = "Coherent Upgrade",
  87         [0x7] = "Coherent Upgrade for Store Conditional",
  88         [0x8] = "Coherent Writeback",
  89         [0x9] = "Coherent Write Invalidate",
  90         [0xa] = "0xa",
  91         [0xb] = "0xb",
  92         [0xc] = "0xc",
  93         [0xd] = "0xd",
  94         [0xe] = "0xe",
  95         [0xf] = "0xf"
  96 };
  97
  98 /* CM3 Tag ECC command group */
  99 static char *cm3_cmd_group[8] = {
 100         [0x0] = "Normal",
 101         [0x1] = "Registers",
 102         [0x2] = "TLB",
 103         [0x3] = "0x3",
 104         [0x4] = "L1I",
 105         [0x5] = "L1D",
 106         [0x6] = "L3",
 107         [0x7] = "L2"
 108 };
 109
 110 static char *cm2_core[8] = {
 111         "Invalid/OK",   "Invalid/Data",
 112         "Shared/OK",    "Shared/Data",
 113         "Modified/OK",  "Modified/Data",
 114         "Exclusive/OK", "Exclusive/Data"
 115 };
 116
 117 static char *cm2_l2_type[4] = {
 118         [0x0] = "None",
 119         [0x1] = "Tag RAM single/double ECC error",
 120         [0x2] = "Data RAM single/double ECC error",
 121         [0x3] = "WS RAM uncorrectable dirty parity"
 122 };
 123
 124 static char *cm2_l2_instr[32] = {
 125         [0x00] = "L2_NOP",
 126         [0x01] = "L2_ERR_CORR",
 127         [0x02] = "L2_TAG_INV",
 128         [0x03] = "L2_WS_CLEAN",
 129         [0x04] = "L2_RD_MDYFY_WR",
 130         [0x05] = "L2_WS_MRU",
 131         [0x06] = "L2_EVICT_LN2",
 132         [0x07] = "0x07",
 133         [0x08] = "L2_EVICT",
 134         [0x09] = "L2_REFL",
 135         [0x0a] = "L2_RD",
 136         [0x0b] = "L2_WR",
 137         [0x0c] = "L2_EVICT_MRU",
 138         [0x0d] = "L2_SYNC",
 139         [0x0e] = "L2_REFL_ERR",
 140         [0x0f] = "0x0f",
 141         [0x10] = "L2_INDX_WB_INV",
 142         [0x11] = "L2_INDX_LD_TAG",
 143         [0x12] = "L2_INDX_ST_TAG",
 144         [0x13] = "L2_INDX_ST_DATA",
 145         [0x14] = "L2_INDX_ST_ECC",
 146         [0x15] = "0x15",
 147         [0x16] = "0x16",
 148         [0x17] = "0x17",
 149         [0x18] = "L2_FTCH_AND_LCK",
 150         [0x19] = "L2_HIT_INV",
 151         [0x1a] = "L2_HIT_WB_INV",
 152         [0x1b] = "L2_HIT_WB",
 153         [0x1c] = "0x1c",
 154         [0x1d] = "0x1d",
 155         [0x1e] = "0x1e",
 156         [0x1f] = "0x1f"
 157 };
 158
 159 static char *cm2_causes[32] = {
 160         "None", "GC_WR_ERR", "GC_RD_ERR", "COH_WR_ERR",
 161         "COH_RD_ERR", "MMIO_WR_ERR", "MMIO_RD_ERR", "0x07",
 162         "0x08", "0x09", "0x0a", "0x0b",
 163         "0x0c", "0x0d", "0x0e", "0x0f",
 164         "0x10", "INTVN_WR_ERR", "INTVN_RD_ERR", "0x13",
 165         "0x14", "0x15", "0x16", "0x17",
 166         "L2_RD_UNCORR", "L2_WR_UNCORR", "L2_CORR", "0x1b",
 167         "0x1c", "0x1d", "0x1e", "0x1f"
 168 };
 169
 170 static char *cm3_causes[32] = {
 171         "0x0", "MP_CORRECTABLE_ECC_ERR", "MP_REQUEST_DECODE_ERR",
 172         "MP_UNCORRECTABLE_ECC_ERR", "MP_PARITY_ERR", "MP_COHERENCE_ERR",
 173         "CMBIU_REQUEST_DECODE_ERR", "CMBIU_PARITY_ERR", "CMBIU_AXI_RESP_ERR",
 174         "0x9", "RBI_BUS_ERR", "0xb", "0xc", "0xd", "0xe", "0xf", "0x10",
 175         "0x11", "0x12", "0x13", "0x14", "0x15", "0x16", "0x17", "0x18",
 176         "0x19", "0x1a", "0x1b", "0x1c", "0x1d", "0x1e", "0x1f"
 177 };
 178
 179 static DEFINE_PER_CPU_ALIGNED(spinlock_t, cm_core_lock);
 180 static DEFINE_PER_CPU_ALIGNED(unsigned long, cm_core_lock_flags);
 181
 182 phys_addr_t __weak mips_cm_phys_base(void)
 183 {
 184         unsigned long cmgcr;
 185
 186         /* Check the CMGCRBase register is implemented */
 187         if (!(read_c0_config() & MIPS_CONF_M))
 188                 return 0;
 189
 190         if (!(read_c0_config2() & MIPS_CONF_M))
 191                 return 0;
 192
 193         if (!(read_c0_config3() & MIPS_CONF3_CMGCR))
 194                 return 0;
 195
 196         /* Read the address from CMGCRBase */
 197         cmgcr = read_c0_cmgcrbase();
 198         return (cmgcr & MIPS_CMGCRF_BASE) << (36 - 32);
 199 }
 200
 201 phys_addr_t __weak mips_cm_l2sync_phys_base(void)
 202 {
 203         u32 base_reg;
 204
 205         /*
 206          * If the L2-only sync region is already enabled then leave it at it's
 207          * current location.
 208          */
 209         base_reg = read_gcr_l2_only_sync_base();
 210         if (base_reg & CM_GCR_L2_ONLY_SYNC_BASE_SYNCEN)
 211                 return base_reg & CM_GCR_L2_ONLY_SYNC_BASE_SYNCBASE;
 212
 213         /* Default to following the CM */
 214         return mips_cm_phys_base() + MIPS_CM_GCR_SIZE;
 215 }
 216
 217 static void mips_cm_probe_l2sync(void)
 218 {
 219         unsigned major_rev;
 220         phys_addr_t addr;
 221
 222         /* L2-only sync was introduced with CM major revision 6 */
 223         major_rev = FIELD_GET(CM_GCR_REV_MAJOR, read_gcr_rev());
 224         if (major_rev < 6)
 225                 return;
 226
 227         /* Find a location for the L2 sync region */
 228         addr = mips_cm_l2sync_phys_base();
 229         BUG_ON((addr & CM_GCR_L2_ONLY_SYNC_BASE_SYNCBASE) != addr);
 230         if (!addr)
 231                 return;
 232
 233         /* Set the region base address & enable it */
 234         write_gcr_l2_only_sync_base(addr | CM_GCR_L2_ONLY_SYNC_BASE_SYNCEN);
 235
 236         /* Map the region */
 237         mips_cm_l2sync_base = ioremap(addr, MIPS_CM_L2SYNC_SIZE);
 238 }
 239
 240 int mips_cm_probe(void)
 241 {
 242         phys_addr_t addr;
 243         u32 base_reg;
 244         unsigned cpu;
 245
 246         /*
 247          * No need to probe again if we have already been
 248          * here before.
 249          */
 250         if (mips_gcr_base)
 251                 return 0;
 252
 253         addr = mips_cm_phys_base();
 254         BUG_ON((addr & CM_GCR_BASE_GCRBASE) != addr);
 255         if (!addr)
 256                 return -ENODEV;
 257
 258         mips_gcr_base = ioremap(addr, MIPS_CM_GCR_SIZE);
 259         if (!mips_gcr_base)
 260                 return -ENXIO;
 261
 262         /* sanity check that we're looking at a CM */
 263         base_reg = read_gcr_base();
 264         if ((base_reg & CM_GCR_BASE_GCRBASE) != addr) {
 265                 pr_err("GCRs appear to have been moved (expected them at 0x%08lx)!\n",
 266                        (unsigned long)addr);
 267                 iounmap(mips_gcr_base);
 268                 mips_gcr_base = NULL;
 269                 return -ENODEV;
 270         }
 271
 272         /* set default target to memory */
 273         change_gcr_base(CM_GCR_BASE_CMDEFTGT, CM_GCR_BASE_CMDEFTGT_MEM);
 274
 275         /* disable CM regions */
 276         write_gcr_reg0_base(CM_GCR_REGn_BASE_BASEADDR);
 277         write_gcr_reg0_mask(CM_GCR_REGn_MASK_ADDRMASK);
 278         write_gcr_reg1_base(CM_GCR_REGn_BASE_BASEADDR);
 279         write_gcr_reg1_mask(CM_GCR_REGn_MASK_ADDRMASK);
 280         write_gcr_reg2_base(CM_GCR_REGn_BASE_BASEADDR);
 281         write_gcr_reg2_mask(CM_GCR_REGn_MASK_ADDRMASK);
 282         write_gcr_reg3_base(CM_GCR_REGn_BASE_BASEADDR);
 283         write_gcr_reg3_mask(CM_GCR_REGn_MASK_ADDRMASK);
 284
 285         /* probe for an L2-only sync region */
 286         mips_cm_probe_l2sync();
 287
 288         /* determine register width for this CM */
 289         mips_cm_is64 = IS_ENABLED(CONFIG_64BIT) && (mips_cm_revision() >= CM_REV_CM3);
 290
 291         for_each_possible_cpu(cpu)
 292                 spin_lock_init(&per_cpu(cm_core_lock, cpu));
 293
 294         return 0;
 295 }
 296
 297 void mips_cm_lock_other(unsigned int cluster, unsigned int core,
 298                         unsigned int vp, unsigned int block)
 299 {
 300         unsigned int curr_core, cm_rev;
 301         u32 val;
 302
 303         cm_rev = mips_cm_revision();
 304         preempt_disable();
 305
 306         if (cm_rev >= CM_REV_CM3) {
 307                 val = FIELD_PREP(CM3_GCR_Cx_OTHER_CORE, core) |
 308                       FIELD_PREP(CM3_GCR_Cx_OTHER_VP, vp);
 309
 310                 if (cm_rev >= CM_REV_CM3_5) {
 311                         val |= CM_GCR_Cx_OTHER_CLUSTER_EN;
 312                         val |= FIELD_PREP(CM_GCR_Cx_OTHER_CLUSTER, cluster);
 313                         val |= FIELD_PREP(CM_GCR_Cx_OTHER_BLOCK, block);
 314                 } else {
 315                         WARN_ON(cluster != 0);
 316                         WARN_ON(block != CM_GCR_Cx_OTHER_BLOCK_LOCAL);
 317                 }
 318
 319                 /*
 320                  * We need to disable interrupts in SMP systems in order to
 321                  * ensure that we don't interrupt the caller with code which
 322                  * may modify the redirect register. We do so here in a
 323                  * slightly obscure way by using a spin lock, since this has
 324                  * the neat property of also catching any nested uses of
 325                  * mips_cm_lock_other() leading to a deadlock or a nice warning
 326                  * with lockdep enabled.
 327                  */
 328                 spin_lock_irqsave(this_cpu_ptr(&cm_core_lock),
 329                                   *this_cpu_ptr(&cm_core_lock_flags));
 330         } else {
 331                 WARN_ON(cluster != 0);
 332                 WARN_ON(block != CM_GCR_Cx_OTHER_BLOCK_LOCAL);
 333
 334                 /*
 335                  * We only have a GCR_CL_OTHER per core in systems with
 336                  * CM 2.5 & older, so have to ensure other VP(E)s don't
 337                  * race with us.
 338                  */
 339                 curr_core = cpu_core(&current_cpu_data);
 340                 spin_lock_irqsave(&per_cpu(cm_core_lock, curr_core),
 341                                   per_cpu(cm_core_lock_flags, curr_core));
 342
 343                 val = FIELD_PREP(CM_GCR_Cx_OTHER_CORENUM, core);
 344         }
 345
 346         write_gcr_cl_other(val);
 347
 348         /*
 349          * Ensure the core-other region reflects the appropriate core &
 350          * VP before any accesses to it occur.
 351          */
 352         mb();
 353 }
 354
 355 void mips_cm_unlock_other(void)
 356 {
 357         unsigned int curr_core;
 358
 359         if (mips_cm_revision() < CM_REV_CM3) {
 360                 curr_core = cpu_core(&current_cpu_data);
 361                 spin_unlock_irqrestore(&per_cpu(cm_core_lock, curr_core),
 362                                        per_cpu(cm_core_lock_flags, curr_core));
 363         } else {
 364                 spin_unlock_irqrestore(this_cpu_ptr(&cm_core_lock),
 365                                        *this_cpu_ptr(&cm_core_lock_flags));
 366         }
 367
 368         preempt_enable();
 369 }
 370
 371 void mips_cm_error_report(void)
 372 {
 373         u64 cm_error, cm_addr, cm_other;
 374         unsigned long revision;
 375         int ocause, cause;
 376         char buf[256];
 377
 378         if (!mips_cm_present())
 379                 return;
 380
 381         revision = mips_cm_revision();
 382         cm_error = read_gcr_error_cause();
 383         cm_addr = read_gcr_error_addr();
 384         cm_other = read_gcr_error_mult();
 385
 386         if (revision < CM_REV_CM3) { /* CM2 */
 387                 cause = FIELD_GET(CM_GCR_ERROR_CAUSE_ERRTYPE, cm_error);
 388                 ocause = FIELD_GET(CM_GCR_ERROR_MULT_ERR2ND, cm_other);
 389
 390                 if (!cause)
 391                         return;
 392
 393                 if (cause < 16) {
 394                         unsigned long cca_bits = (cm_error >> 15) & 7;
 395                         unsigned long tr_bits = (cm_error >> 12) & 7;
 396                         unsigned long cmd_bits = (cm_error >> 7) & 0x1f;
 397                         unsigned long stag_bits = (cm_error >> 3) & 15;
 398                         unsigned long sport_bits = (cm_error >> 0) & 7;
 399
 400                         snprintf(buf, sizeof(buf),
 401                                  "CCA=%lu TR=%s MCmd=%s STag=%lu "
 402                                  "SPort=%lu\n", cca_bits, cm2_tr[tr_bits],
 403                                  cm2_cmd[cmd_bits], stag_bits, sport_bits);
 404                 } else if (cause < 24) {
 405                         /* glob state & sresp together */
 406                         unsigned long c3_bits = (cm_error >> 18) & 7;
 407                         unsigned long c2_bits = (cm_error >> 15) & 7;
 408                         unsigned long c1_bits = (cm_error >> 12) & 7;
 409                         unsigned long c0_bits = (cm_error >> 9) & 7;
 410                         unsigned long sc_bit = (cm_error >> 8) & 1;
 411                         unsigned long cmd_bits = (cm_error >> 3) & 0x1f;
 412                         unsigned long sport_bits = (cm_error >> 0) & 7;
 413
 414                         snprintf(buf, sizeof(buf),
 415                                  "C3=%s C2=%s C1=%s C0=%s SC=%s "
 416                                  "MCmd=%s SPort=%lu\n",
 417                                  cm2_core[c3_bits], cm2_core[c2_bits],
 418                                  cm2_core[c1_bits], cm2_core[c0_bits],
 419                                  sc_bit ? "True" : "False",
 420                                  cm2_cmd[cmd_bits], sport_bits);
 421                 } else {
 422                         unsigned long muc_bit = (cm_error >> 23) & 1;
 423                         unsigned long ins_bits = (cm_error >> 18) & 0x1f;
 424                         unsigned long arr_bits = (cm_error >> 16) & 3;
 425                         unsigned long dw_bits = (cm_error >> 12) & 15;
 426                         unsigned long way_bits = (cm_error >> 9) & 7;
 427                         unsigned long mway_bit = (cm_error >> 8) & 1;
 428                         unsigned long syn_bits = (cm_error >> 0) & 0xFF;
 429
 430                         snprintf(buf, sizeof(buf),
 431                                  "Type=%s%s Instr=%s DW=%lu Way=%lu "
 432                                  "MWay=%s Syndrome=0x%02lx",
 433                                  muc_bit ? "Multi-UC " : "",
 434                                  cm2_l2_type[arr_bits],
 435                                  cm2_l2_instr[ins_bits], dw_bits, way_bits,
 436                                  mway_bit ? "True" : "False", syn_bits);
 437                 }
 438                 pr_err("CM_ERROR=%08llx %s <%s>\n", cm_error,
 439                        cm2_causes[cause], buf);
 440                 pr_err("CM_ADDR =%08llx\n", cm_addr);
 441                 pr_err("CM_OTHER=%08llx %s\n", cm_other, cm2_causes[ocause]);
 442         } else { /* CM3 */
 443                 ulong core_id_bits, vp_id_bits, cmd_bits, cmd_group_bits;
 444                 ulong cm3_cca_bits, mcp_bits, cm3_tr_bits, sched_bit;
 445
 446                 cause = FIELD_GET(CM3_GCR_ERROR_CAUSE_ERRTYPE, cm_error);
 447                 ocause = FIELD_GET(CM_GCR_ERROR_MULT_ERR2ND, cm_other);
 448
 449                 if (!cause)
 450                         return;
 451
 452                 /* Used by cause == {1,2,3} */
 453                 core_id_bits = (cm_error >> 22) & 0xf;
 454                 vp_id_bits = (cm_error >> 18) & 0xf;
 455                 cmd_bits = (cm_error >> 14) & 0xf;
 456                 cmd_group_bits = (cm_error >> 11) & 0xf;
 457                 cm3_cca_bits = (cm_error >> 8) & 7;
 458                 mcp_bits = (cm_error >> 5) & 0xf;
 459                 cm3_tr_bits = (cm_error >> 1) & 0xf;
 460                 sched_bit = cm_error & 0x1;
 461
 462                 if (cause == 1 || cause == 3) { /* Tag ECC */
 463                         unsigned long tag_ecc = (cm_error >> 57) & 0x1;
 464                         unsigned long tag_way_bits = (cm_error >> 29) & 0xffff;
 465                         unsigned long dword_bits = (cm_error >> 49) & 0xff;
 466                         unsigned long data_way_bits = (cm_error >> 45) & 0xf;
 467                         unsigned long data_sets_bits = (cm_error >> 29) & 0xfff;
 468                         unsigned long bank_bit = (cm_error >> 28) & 0x1;
 469                         snprintf(buf, sizeof(buf),
 470                                  "%s ECC Error: Way=%lu (DWORD=%lu, Sets=%lu)"
 471                                  "Bank=%lu CoreID=%lu VPID=%lu Command=%s"
 472                                  "Command Group=%s CCA=%lu MCP=%d"
 473                                  "Transaction type=%s Scheduler=%lu\n",
 474                                  tag_ecc ? "TAG" : "DATA",
 475                                  tag_ecc ? (unsigned long)ffs(tag_way_bits) - 1 :
 476                                  data_way_bits, bank_bit, dword_bits,
 477                                  data_sets_bits,
 478                                  core_id_bits, vp_id_bits,
 479                                  cm3_cmd[cmd_bits],
 480                                  cm3_cmd_group[cmd_group_bits],
 481                                  cm3_cca_bits, 1 << mcp_bits,
 482                                  cm3_tr[cm3_tr_bits], sched_bit);
 483                 } else if (cause == 2) {
 484                         unsigned long data_error_type = (cm_error >> 41) & 0xfff;
 485                         unsigned long data_decode_cmd = (cm_error >> 37) & 0xf;
 486                         unsigned long data_decode_group = (cm_error >> 34) & 0x7;
 487                         unsigned long data_decode_destination_id = (cm_error >> 28) & 0x3f;
 488
 489                         snprintf(buf, sizeof(buf),
 490                                  "Decode Request Error: Type=%lu, Command=%lu"
 491                                  "Command Group=%lu Destination ID=%lu"
 492                                  "CoreID=%lu VPID=%lu Command=%s"
 493                                  "Command Group=%s CCA=%lu MCP=%d"
 494                                  "Transaction type=%s Scheduler=%lu\n",
 495                                  data_error_type, data_decode_cmd,
 496                                  data_decode_group, data_decode_destination_id,
 497                                  core_id_bits, vp_id_bits,
 498                                  cm3_cmd[cmd_bits],
 499                                  cm3_cmd_group[cmd_group_bits],
 500                                  cm3_cca_bits, 1 << mcp_bits,
 501                                  cm3_tr[cm3_tr_bits], sched_bit);
 502                 } else {
 503                         buf[0] = 0;
 504                 }
 505
 506                 pr_err("CM_ERROR=%llx %s <%s>\n", cm_error,
 507                        cm3_causes[cause], buf);
 508                 pr_err("CM_ADDR =%llx\n", cm_addr);
 509                 pr_err("CM_OTHER=%llx %s\n", cm_other, cm3_causes[ocause]);
 510         }
 511
 512         /* reprime cause register */
 513         write_gcr_error_cause(cm_error);
 514 }
 515
 516 unsigned int mips_cps_first_online_in_cluster(void)
 517 {
 518         unsigned int local_cl;
 519         int i;
 520
 521         local_cl = cpu_cluster(&current_cpu_data);
 522
 523         /*
 524          * We rely upon knowledge that CPUs are numbered sequentially by
 525          * cluster - ie. CPUs 0..X will be in cluster 0, CPUs X+1..Y in cluster
 526          * 1, CPUs Y+1..Z in cluster 2 etc. This means that CPUs in the same
 527          * cluster will immediately precede or follow one another.
 528          *
 529          * First we scan backwards, until we find an online CPU in the cluster
 530          * or we move on to another cluster.
 531          */
 532         for (i = smp_processor_id() - 1; i >= 0; i--) {
 533                 if (cpu_cluster(&cpu_data[i]) != local_cl)
 534                         break;
 535                 if (!cpu_online(i))
 536                         continue;
 537                 return false;
 538         }
 539
 540         /* Then do the same for higher numbered CPUs */
 541         for (i = smp_processor_id() + 1; i < nr_cpu_ids; i++) {
 542                 if (cpu_cluster(&cpu_data[i]) != local_cl)
 543                         break;
 544                 if (!cpu_online(i))
 545                         continue;
 546                 return false;
 547         }
 548
 549         /* We found no online CPUs in the local cluster */
 550         return true;
 551 }