root/arch/xtensa/kernel/s32c1i_selftest.c

DEFINITIONS

1. probed_compare_swap
2. do_probed_exception
3. check_s32c1i
4. check_s32c1i

   1 /*
   2  * S32C1I selftest.
   3  *
   4  * This file is subject to the terms and conditions of the GNU General Public
   5  * License.  See the file "COPYING" in the main directory of this archive
   6  * for more details.
   7  *
   8  * Copyright (C) 2016 Cadence Design Systems Inc.
   9  */
  10 
  11 #include <linux/init.h>
  12 #include <linux/kernel.h>
  13 
  14 #include <asm/traps.h>
  15 
  16 #if XCHAL_HAVE_S32C1I
  17 
  18 static int __initdata rcw_word, rcw_probe_pc, rcw_exc;
  19 
  20 /*
  21  * Basic atomic compare-and-swap, that records PC of S32C1I for probing.
  22  *
  23  * If *v == cmp, set *v = set.  Return previous *v.
  24  */
  25 static inline int probed_compare_swap(int *v, int cmp, int set)
  26 {
  27         int tmp;
  28 
  29         __asm__ __volatile__(
  30                         "       movi    %1, 1f\n"
  31                         "       s32i    %1, %4, 0\n"
  32                         "       wsr     %2, scompare1\n"
  33                         "1:     s32c1i  %0, %3, 0\n"
  34                         : "=a" (set), "=&a" (tmp)
  35                         : "a" (cmp), "a" (v), "a" (&rcw_probe_pc), "0" (set)
  36                         : "memory"
  37                         );
  38         return set;
  39 }
  40 
  41 /* Handle probed exception */
  42 
  43 static void __init do_probed_exception(struct pt_regs *regs,
  44                                        unsigned long exccause)
  45 {
  46         if (regs->pc == rcw_probe_pc) { /* exception on s32c1i ? */
  47                 regs->pc += 3;          /* skip the s32c1i instruction */
  48                 rcw_exc = exccause;
  49         } else {
  50                 do_unhandled(regs, exccause);
  51         }
  52 }
  53 
  54 /* Simple test of S32C1I (soc bringup assist) */
  55 
  56 static int __init check_s32c1i(void)
  57 {
  58         int n, cause1, cause2;
  59         void *handbus, *handdata, *handaddr; /* temporarily saved handlers */
  60 
  61         rcw_probe_pc = 0;
  62         handbus  = trap_set_handler(EXCCAUSE_LOAD_STORE_ERROR,
  63                         do_probed_exception);
  64         handdata = trap_set_handler(EXCCAUSE_LOAD_STORE_DATA_ERROR,
  65                         do_probed_exception);
  66         handaddr = trap_set_handler(EXCCAUSE_LOAD_STORE_ADDR_ERROR,
  67                         do_probed_exception);
  68 
  69         /* First try an S32C1I that does not store: */
  70         rcw_exc = 0;
  71         rcw_word = 1;
  72         n = probed_compare_swap(&rcw_word, 0, 2);
  73         cause1 = rcw_exc;
  74 
  75         /* took exception? */
  76         if (cause1 != 0) {
  77                 /* unclean exception? */
  78                 if (n != 2 || rcw_word != 1)
  79                         panic("S32C1I exception error");
  80         } else if (rcw_word != 1 || n != 1) {
  81                 panic("S32C1I compare error");
  82         }
  83 
  84         /* Then an S32C1I that stores: */
  85         rcw_exc = 0;
  86         rcw_word = 0x1234567;
  87         n = probed_compare_swap(&rcw_word, 0x1234567, 0xabcde);
  88         cause2 = rcw_exc;
  89 
  90         if (cause2 != 0) {
  91                 /* unclean exception? */
  92                 if (n != 0xabcde || rcw_word != 0x1234567)
  93                         panic("S32C1I exception error (b)");
  94         } else if (rcw_word != 0xabcde || n != 0x1234567) {
  95                 panic("S32C1I store error");
  96         }
  97 
  98         /* Verify consistency of exceptions: */
  99         if (cause1 || cause2) {
 100                 pr_warn("S32C1I took exception %d, %d\n", cause1, cause2);
 101                 /* If emulation of S32C1I upon bus error gets implemented,
 102                  * we can get rid of this panic for single core (not SMP)
 103                  */
 104                 panic("S32C1I exceptions not currently supported");
 105         }
 106         if (cause1 != cause2)
 107                 panic("inconsistent S32C1I exceptions");
 108 
 109         trap_set_handler(EXCCAUSE_LOAD_STORE_ERROR, handbus);
 110         trap_set_handler(EXCCAUSE_LOAD_STORE_DATA_ERROR, handdata);
 111         trap_set_handler(EXCCAUSE_LOAD_STORE_ADDR_ERROR, handaddr);
 112         return 0;
 113 }
 114 
 115 #else /* XCHAL_HAVE_S32C1I */
 116 
 117 /* This condition should not occur with a commercially deployed processor.
 118  * Display reminder for early engr test or demo chips / FPGA bitstreams
 119  */
 120 static int __init check_s32c1i(void)
 121 {
 122         pr_warn("Processor configuration lacks atomic compare-and-swap support!\n");
 123         return 0;
 124 }
 125 
 126 #endif /* XCHAL_HAVE_S32C1I */
 127 
 128 early_initcall(check_s32c1i);