1 // SPDX-License-Identifier: GPL-2.0
2 /* Tests for presence or absence of hardware registers.
3 * This code was originally in atari/config.c, but I noticed
4 * that it was also in drivers/nubus/nubus.c and I wanted to
5 * use it in hp300/config.c, so it seemed sensible to pull it
6 * out into its own file.
7 *
8 * The test is for use when trying to read a hardware register
9 * that isn't present would cause a bus error. We set up a
10 * temporary handler so that this doesn't kill the kernel.
11 *
12 * There is a test-by-reading and a test-by-writing; I present
13 * them here complete with the comments from the original atari
14 * config.c...
15 * -- PMM <pmaydell@chiark.greenend.org.uk>, 05/1998
16 */
17
18 /* This function tests for the presence of an address, specially a
19 * hardware register address. It is called very early in the kernel
20 * initialization process, when the VBR register isn't set up yet. On
21 * an Atari, it still points to address 0, which is unmapped. So a bus
22 * error would cause another bus error while fetching the exception
23 * vector, and the CPU would do nothing at all. So we needed to set up
24 * a temporary VBR and a vector table for the duration of the test.
25 */
26
27 #include <linux/module.h>
28
29 #include <asm/hwtest.h>
30
31 int hwreg_present(volatile void *regp)
32 {
33 int ret = 0;
34 unsigned long flags;
35 long save_sp, save_vbr;
36 long tmp_vectors[3];
37
38 local_irq_save(flags);
39 __asm__ __volatile__ (
40 "movec %/vbr,%2\n\t"
41 "movel #Lberr1,%4@(8)\n\t"
42 "movec %4,%/vbr\n\t"
43 "movel %/sp,%1\n\t"
44 "moveq #0,%0\n\t"
45 "tstb %3@\n\t"
46 "nop\n\t"
47 "moveq #1,%0\n"
48 "Lberr1:\n\t"
49 "movel %1,%/sp\n\t"
50 "movec %2,%/vbr"
51 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
52 : "a" (regp), "a" (tmp_vectors)
53 );
54 local_irq_restore(flags);
55
56 return ret;
57 }
58 EXPORT_SYMBOL(hwreg_present);
59
60 /* Basically the same, but writes a value into a word register, protected
61 * by a bus error handler. Returns 1 if successful, 0 otherwise.
62 */
63
64 int hwreg_write(volatile void *regp, unsigned short val)
65 {
66 int ret;
67 unsigned long flags;
68 long save_sp, save_vbr;
69 long tmp_vectors[3];
70
71 local_irq_save(flags);
72 __asm__ __volatile__ (
73 "movec %/vbr,%2\n\t"
74 "movel #Lberr2,%4@(8)\n\t"
75 "movec %4,%/vbr\n\t"
76 "movel %/sp,%1\n\t"
77 "moveq #0,%0\n\t"
78 "movew %5,%3@\n\t"
79 "nop\n\t"
80 /*
81 * If this nop isn't present, 'ret' may already be loaded
82 * with 1 at the time the bus error happens!
83 */
84 "moveq #1,%0\n"
85 "Lberr2:\n\t"
86 "movel %1,%/sp\n\t"
87 "movec %2,%/vbr"
88 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
89 : "a" (regp), "a" (tmp_vectors), "g" (val)
90 );
91 local_irq_restore(flags);
92
93 return ret;
94 }
95 EXPORT_SYMBOL(hwreg_write);
96
97
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