Commit | Line | Data |
---|---|---|
1da177e4 LT |
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 | ||
24cae793 | 28 | int hwreg_present(volatile void *regp) |
1da177e4 | 29 | { |
24cae793 GU |
30 | int ret = 0; |
31 | unsigned long flags; | |
32 | long save_sp, save_vbr; | |
33 | long tmp_vectors[3]; | |
1da177e4 | 34 | |
24cae793 GU |
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" | |
1da177e4 | 43 | "nop\n\t" |
24cae793 GU |
44 | "moveq #1,%0\n" |
45 | "Lberr1:\n\t" | |
46 | "movel %1,%/sp\n\t" | |
47 | "movec %2,%/vbr" | |
1da177e4 LT |
48 | : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr) |
49 | : "a" (regp), "a" (tmp_vectors) | |
24cae793 GU |
50 | ); |
51 | local_irq_restore(flags); | |
1da177e4 | 52 | |
24cae793 | 53 | return ret; |
1da177e4 LT |
54 | } |
55 | EXPORT_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 | ||
24cae793 | 61 | int hwreg_write(volatile void *regp, unsigned short val) |
1da177e4 | 62 | { |
24cae793 | 63 | int ret; |
e4dc601b | 64 | unsigned long flags; |
24cae793 GU |
65 | long save_sp, save_vbr; |
66 | long tmp_vectors[3]; | |
1da177e4 | 67 | |
e4dc601b | 68 | local_irq_save(flags); |
24cae793 GU |
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" | |
1da177e4 | 82 | "Lberr2:\n\t" |
24cae793 GU |
83 | "movel %1,%/sp\n\t" |
84 | "movec %2,%/vbr" | |
1da177e4 LT |
85 | : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr) |
86 | : "a" (regp), "a" (tmp_vectors), "g" (val) | |
87 | ); | |
e4dc601b | 88 | local_irq_restore(flags); |
1da177e4 | 89 | |
24cae793 | 90 | return ret; |
1da177e4 LT |
91 | } |
92 | EXPORT_SYMBOL(hwreg_write); | |
93 |