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
hwreg_present(volatile void * regp)26 int hwreg_present( volatile void *regp )
27 {
28 int ret = 0;
29 long save_sp, save_vbr;
30 long tmp_vectors[3];
31
32 __asm__ __volatile__
33 ( "movec %/vbr,%2\n\t"
34 "movel #Lberr1,%4@(8)\n\t"
35 "movec %4,%/vbr\n\t"
36 "movel %/sp,%1\n\t"
37 "moveq #0,%0\n\t"
38 "tstb %3@\n\t"
39 "nop\n\t"
40 "moveq #1,%0\n"
41 "Lberr1:\n\t"
42 "movel %1,%/sp\n\t"
43 "movec %2,%/vbr"
44 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
45 : "a" (regp), "a" (tmp_vectors)
46 );
47
48 return( ret );
49 }
50
51 /* Basically the same, but writes a value into a word register, protected
52 * by a bus error handler. Returns 1 if successful, 0 otherwise.
53 */
54
hwreg_write(volatile void * regp,unsigned short val)55 int hwreg_write( volatile void *regp, unsigned short val )
56 {
57 int ret;
58 long save_sp, save_vbr;
59 long tmp_vectors[3];
60
61 __asm__ __volatile__
62 ( "movec %/vbr,%2\n\t"
63 "movel #Lberr2,%4@(8)\n\t"
64 "movec %4,%/vbr\n\t"
65 "movel %/sp,%1\n\t"
66 "moveq #0,%0\n\t"
67 "movew %5,%3@\n\t"
68 "nop \n\t" /* If this nop isn't present, 'ret' may already be
69 * loaded with 1 at the time the bus error
70 * happens! */
71 "moveq #1,%0\n"
72 "Lberr2:\n\t"
73 "movel %1,%/sp\n\t"
74 "movec %2,%/vbr"
75 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
76 : "a" (regp), "a" (tmp_vectors), "g" (val)
77 );
78
79 return( ret );
80 }
81
82