Release 4.14 arch/m68k/mm/hwtest.c

// SPDX-License-Identifier: GPL-2.0
/* Tests for presence or absence of hardware registers.
 * This code was originally in atari/config.c, but I noticed
 * that it was also in drivers/nubus/nubus.c and I wanted to
 * use it in hp300/config.c, so it seemed sensible to pull it
 * out into its own file.
 *
 * The test is for use when trying to read a hardware register
 * that isn't present would cause a bus error. We set up a
 * temporary handler so that this doesn't kill the kernel.
 *
 * There is a test-by-reading and a test-by-writing; I present
 * them here complete with the comments from the original atari
 * config.c...
 *                -- PMM <pmaydell@chiark.greenend.org.uk>, 05/1998
 */

/* This function tests for the presence of an address, specially a
 * hardware register address. It is called very early in the kernel
 * initialization process, when the VBR register isn't set up yet. On
 * an Atari, it still points to address 0, which is unmapped. So a bus
 * error would cause another bus error while fetching the exception
 * vector, and the CPU would do nothing at all. So we needed to set up
 * a temporary VBR and a vector table for the duration of the test.
 */

#include <linux/module.h>



int hwreg_present(volatile void *regp)
{
	int ret = 0;
	unsigned long flags;
	long save_sp, save_vbr;
	long tmp_vectors[3];

	local_irq_save(flags);
	__asm__ __volatile__ (
                "movec %/vbr,%2\n\t"
                "movel #Lberr1,%4@(8)\n\t"
                "movec %4,%/vbr\n\t"
                "movel %/sp,%1\n\t"
                "moveq #0,%0\n\t"
                "tstb %3@\n\t"
                "nop\n\t"
                "moveq #1,%0\n"
        "Lberr1:\n\t"
                "movel %1,%/sp\n\t"
                "movec %2,%/vbr"
                : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
                : "a" (regp), "a" (tmp_vectors)
        );
	local_irq_restore(flags);

	return ret;
}
Contributors
Person
Tokens
Prop
Commits
CommitProp
Linus Torvalds (pre-git)
31
67.39%
1
33.33%
Geert Uytterhoeven
15
32.61%
2
66.67%
Total
46
100.00%
3
100.00%


EXPORT_SYMBOL(hwreg_present);

/* Basically the same, but writes a value into a word register, protected
 * by a bus error handler. Returns 1 if successful, 0 otherwise.
 */



int hwreg_write(volatile void *regp, unsigned short val)
{
	int ret;
	unsigned long flags;
	long save_sp, save_vbr;
	long tmp_vectors[3];

	local_irq_save(flags);
	__asm__ __volatile__ (
                "movec %/vbr,%2\n\t"
                "movel #Lberr2,%4@(8)\n\t"
                "movec %4,%/vbr\n\t"
                "movel %/sp,%1\n\t"
                "moveq #0,%0\n\t"
                "movew %5,%3@\n\t"
                "nop\n\t"
		/*
                 * If this nop isn't present, 'ret' may already be loaded
                 * with 1 at the time the bus error happens!
                 */
		"moveq #1,%0\n"
        "Lberr2:\n\t"
                "movel %1,%/sp\n\t"
                "movec %2,%/vbr"
                : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
                : "a" (regp), "a" (tmp_vectors), "g" (val)
        );
	local_irq_restore(flags);

	return ret;
}
Contributors
Person
Tokens
Prop
Commits
CommitProp
Linus Torvalds (pre-git)
33
66.00%
1
33.33%
Geert Uytterhoeven
17
34.00%
2
66.67%
Total
50
100.00%
3
100.00%


EXPORT_SYMBOL(hwreg_write);

Overall Contributors
Person
Tokens
Prop
Commits
CommitProp
Linus Torvalds (pre-git)
66
58.41%
1
16.67%
Geert Uytterhoeven
33
29.20%
3
50.00%
Andrew Morton
13
11.50%
1
16.67%
Greg Kroah-Hartman
1
0.88%
1
16.67%
Total
113
100.00%
6
100.00%
Directory: arch/m68k/mm

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