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// 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;
}
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;
}
EXPORT_SYMBOL(hwreg_write);
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