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