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  */
probed_compare_swap(int * v,int cmp,int set)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 
do_probed_exception(struct pt_regs * regs)43 static void __init do_probed_exception(struct pt_regs *regs)
44 {
45 	if (regs->pc == rcw_probe_pc) {	/* exception on s32c1i ? */
46 		regs->pc += 3;		/* skip the s32c1i instruction */
47 		rcw_exc = regs->exccause;
48 	} else {
49 		do_unhandled(regs);
50 	}
51 }
52 
53 /* Simple test of S32C1I (soc bringup assist) */
54 
check_s32c1i(void)55 static int __init check_s32c1i(void)
56 {
57 	int n, cause1, cause2;
58 	void *handbus, *handdata, *handaddr; /* temporarily saved handlers */
59 
60 	rcw_probe_pc = 0;
61 	handbus  = trap_set_handler(EXCCAUSE_LOAD_STORE_ERROR,
62 			do_probed_exception);
63 	handdata = trap_set_handler(EXCCAUSE_LOAD_STORE_DATA_ERROR,
64 			do_probed_exception);
65 	handaddr = trap_set_handler(EXCCAUSE_LOAD_STORE_ADDR_ERROR,
66 			do_probed_exception);
67 
68 	/* First try an S32C1I that does not store: */
69 	rcw_exc = 0;
70 	rcw_word = 1;
71 	n = probed_compare_swap(&rcw_word, 0, 2);
72 	cause1 = rcw_exc;
73 
74 	/* took exception? */
75 	if (cause1 != 0) {
76 		/* unclean exception? */
77 		if (n != 2 || rcw_word != 1)
78 			panic("S32C1I exception error");
79 	} else if (rcw_word != 1 || n != 1) {
80 		panic("S32C1I compare error");
81 	}
82 
83 	/* Then an S32C1I that stores: */
84 	rcw_exc = 0;
85 	rcw_word = 0x1234567;
86 	n = probed_compare_swap(&rcw_word, 0x1234567, 0xabcde);
87 	cause2 = rcw_exc;
88 
89 	if (cause2 != 0) {
90 		/* unclean exception? */
91 		if (n != 0xabcde || rcw_word != 0x1234567)
92 			panic("S32C1I exception error (b)");
93 	} else if (rcw_word != 0xabcde || n != 0x1234567) {
94 		panic("S32C1I store error");
95 	}
96 
97 	/* Verify consistency of exceptions: */
98 	if (cause1 || cause2) {
99 		pr_warn("S32C1I took exception %d, %d\n", cause1, cause2);
100 		/* If emulation of S32C1I upon bus error gets implemented,
101 		 * we can get rid of this panic for single core (not SMP)
102 		 */
103 		panic("S32C1I exceptions not currently supported");
104 	}
105 	if (cause1 != cause2)
106 		panic("inconsistent S32C1I exceptions");
107 
108 	trap_set_handler(EXCCAUSE_LOAD_STORE_ERROR, handbus);
109 	trap_set_handler(EXCCAUSE_LOAD_STORE_DATA_ERROR, handdata);
110 	trap_set_handler(EXCCAUSE_LOAD_STORE_ADDR_ERROR, handaddr);
111 	return 0;
112 }
113 
114 #else /* XCHAL_HAVE_S32C1I */
115 
116 /* This condition should not occur with a commercially deployed processor.
117  * Display reminder for early engr test or demo chips / FPGA bitstreams
118  */
check_s32c1i(void)119 static int __init check_s32c1i(void)
120 {
121 	pr_warn("Processor configuration lacks atomic compare-and-swap support!\n");
122 	return 0;
123 }
124 
125 #endif /* XCHAL_HAVE_S32C1I */
126 
127 early_initcall(check_s32c1i);
128