blob: fb8be4dd38c448d75382bf5a32daf55eff0f4a03 [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001/* 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
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020028int hwreg_present(volatile void *regp)
Linus Torvalds1da177e2005-04-16 15:20:36 -070029{
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020030 int ret = 0;
31 unsigned long flags;
32 long save_sp, save_vbr;
33 long tmp_vectors[3];
Linus Torvalds1da177e2005-04-16 15:20:36 -070034
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020035 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"
Linus Torvalds1da177e2005-04-16 15:20:36 -070043 "nop\n\t"
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020044 "moveq #1,%0\n"
45 "Lberr1:\n\t"
46 "movel %1,%/sp\n\t"
47 "movec %2,%/vbr"
Linus Torvalds1da177e2005-04-16 15:20:36 -070048 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
49 : "a" (regp), "a" (tmp_vectors)
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020050 );
51 local_irq_restore(flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -070052
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020053 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -070054}
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
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020061int hwreg_write(volatile void *regp, unsigned short val)
Linus Torvalds1da177e2005-04-16 15:20:36 -070062{
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020063 int ret;
Geert Uytterhoevene4dc6012014-09-28 10:50:06 +020064 unsigned long flags;
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020065 long save_sp, save_vbr;
66 long tmp_vectors[3];
Linus Torvalds1da177e2005-04-16 15:20:36 -070067
Geert Uytterhoevene4dc6012014-09-28 10:50:06 +020068 local_irq_save(flags);
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020069 __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"
Linus Torvalds1da177e2005-04-16 15:20:36 -070082 "Lberr2:\n\t"
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020083 "movel %1,%/sp\n\t"
84 "movec %2,%/vbr"
Linus Torvalds1da177e2005-04-16 15:20:36 -070085 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
86 : "a" (regp), "a" (tmp_vectors), "g" (val)
87 );
Geert Uytterhoevene4dc6012014-09-28 10:50:06 +020088 local_irq_restore(flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -070089
Geert Uytterhoeven24cae792014-09-28 11:18:49 +020090 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -070091}
92EXPORT_SYMBOL(hwreg_write);
93