xref: /openbmc/linux/arch/m68k/mm/hwtest.c (revision 24cae793)
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 
28 int 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 }
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 
61 int 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 }
92 EXPORT_SYMBOL(hwreg_write);
93 
94