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
29int hwreg_present(volatile void *regp)
30{
31	int ret = 0;
32	unsigned long flags;
33	long save_sp, save_vbr;
34	long tmp_vectors[3];
35
36	local_irq_save(flags);
37	__asm__ __volatile__ (
38		"movec %/vbr,%2\n\t"
39		"movel #Lberr1,%4@(8)\n\t"
40		"movec %4,%/vbr\n\t"
41		"movel %/sp,%1\n\t"
42		"moveq #0,%0\n\t"
43		"tstb %3@\n\t"
44		"nop\n\t"
45		"moveq #1,%0\n"
46	"Lberr1:\n\t"
47		"movel %1,%/sp\n\t"
48		"movec %2,%/vbr"
49		: "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
50		: "a" (regp), "a" (tmp_vectors)
51	);
52	local_irq_restore(flags);
53
54	return ret;
55}
56EXPORT_SYMBOL(hwreg_present);
57
58/* Basically the same, but writes a value into a word register, protected
59 * by a bus error handler. Returns 1 if successful, 0 otherwise.
60 */
61
62int hwreg_write(volatile void *regp, unsigned short val)
63{
64	int ret;
65	unsigned long flags;
66	long save_sp, save_vbr;
67	long tmp_vectors[3];
68
69	local_irq_save(flags);
70	__asm__ __volatile__ (
71		"movec %/vbr,%2\n\t"
72		"movel #Lberr2,%4@(8)\n\t"
73		"movec %4,%/vbr\n\t"
74		"movel %/sp,%1\n\t"
75		"moveq #0,%0\n\t"
76		"movew %5,%3@\n\t"
77		"nop\n\t"
78		/*
79		 * If this nop isn't present, 'ret' may already be loaded
80		 * with 1 at the time the bus error happens!
81		 */
82		"moveq #1,%0\n"
83	"Lberr2:\n\t"
84		"movel %1,%/sp\n\t"
85		"movec %2,%/vbr"
86		: "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
87		: "a" (regp), "a" (tmp_vectors), "g" (val)
88	);
89	local_irq_restore(flags);
90
91	return ret;
92}
93EXPORT_SYMBOL(hwreg_write);
94

 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
29int hwreg_present(volatile void *regp)
30{
31	int ret = 0;
32	unsigned long flags;
33	long save_sp, save_vbr;
34	long tmp_vectors[3];
35
36	local_irq_save(flags);
37	__asm__ __volatile__ (
38		"movec %/vbr,%2\n\t"
39		"movel #Lberr1,%4@(8)\n\t"
40		"movec %4,%/vbr\n\t"
41		"movel %/sp,%1\n\t"
42		"moveq #0,%0\n\t"
43		"tstb %3@\n\t"
44		"nop\n\t"
45		"moveq #1,%0\n"
46	"Lberr1:\n\t"
47		"movel %1,%/sp\n\t"
48		"movec %2,%/vbr"
49		: "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
50		: "a" (regp), "a" (tmp_vectors)
51	);
52	local_irq_restore(flags);
53
54	return ret;
55}
56EXPORT_SYMBOL(hwreg_present);
57
58/* Basically the same, but writes a value into a word register, protected
59 * by a bus error handler. Returns 1 if successful, 0 otherwise.
60 */
61
62int hwreg_write(volatile void *regp, unsigned short val)
63{
64	int ret;
65	unsigned long flags;
66	long save_sp, save_vbr;
67	long tmp_vectors[3];
68
69	local_irq_save(flags);
70	__asm__ __volatile__ (
71		"movec %/vbr,%2\n\t"
72		"movel #Lberr2,%4@(8)\n\t"
73		"movec %4,%/vbr\n\t"
74		"movel %/sp,%1\n\t"
75		"moveq #0,%0\n\t"
76		"movew %5,%3@\n\t"
77		"nop\n\t"
78		/*
79		 * If this nop isn't present, 'ret' may already be loaded
80		 * with 1 at the time the bus error happens!
81		 */
82		"moveq #1,%0\n"
83	"Lberr2:\n\t"
84		"movel %1,%/sp\n\t"
85		"movec %2,%/vbr"
86		: "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
87		: "a" (regp), "a" (tmp_vectors), "g" (val)
88	);
89	local_irq_restore(flags);
90
91	return ret;
92}
93EXPORT_SYMBOL(hwreg_write);
94