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94 lines
2.6 KiB
94 lines
2.6 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* Tests for presence or absence of hardware registers. |
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* This code was originally in atari/config.c, but I noticed |
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* that it was also in drivers/nubus/nubus.c and I wanted to |
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* use it in hp300/config.c, so it seemed sensible to pull it |
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* out into its own file. |
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* |
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* The test is for use when trying to read a hardware register |
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* that isn't present would cause a bus error. We set up a |
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* temporary handler so that this doesn't kill the kernel. |
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* |
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* There is a test-by-reading and a test-by-writing; I present |
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* them here complete with the comments from the original atari |
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* config.c... |
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* -- PMM <[email protected]>, 05/1998 |
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*/ |
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/* This function tests for the presence of an address, specially a |
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* hardware register address. It is called very early in the kernel |
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* initialization process, when the VBR register isn't set up yet. On |
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* an Atari, it still points to address 0, which is unmapped. So a bus |
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* error would cause another bus error while fetching the exception |
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* vector, and the CPU would do nothing at all. So we needed to set up |
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* a temporary VBR and a vector table for the duration of the test. |
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*/ |
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#include <linux/module.h> |
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int hwreg_present(volatile void *regp) |
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{ |
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int ret = 0; |
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unsigned long flags; |
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long save_sp, save_vbr; |
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long tmp_vectors[3]; |
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local_irq_save(flags); |
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__asm__ __volatile__ ( |
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"movec %/vbr,%2\n\t" |
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"movel #Lberr1,%4@(8)\n\t" |
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"movec %4,%/vbr\n\t" |
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"movel %/sp,%1\n\t" |
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"moveq #0,%0\n\t" |
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"tstb %3@\n\t" |
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"nop\n\t" |
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"moveq #1,%0\n" |
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"Lberr1:\n\t" |
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"movel %1,%/sp\n\t" |
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"movec %2,%/vbr" |
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: "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr) |
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: "a" (regp), "a" (tmp_vectors) |
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); |
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local_irq_restore(flags); |
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return ret; |
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} |
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EXPORT_SYMBOL(hwreg_present); |
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/* Basically the same, but writes a value into a word register, protected |
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* by a bus error handler. Returns 1 if successful, 0 otherwise. |
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*/ |
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int hwreg_write(volatile void *regp, unsigned short val) |
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{ |
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int ret; |
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unsigned long flags; |
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long save_sp, save_vbr; |
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long tmp_vectors[3]; |
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local_irq_save(flags); |
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__asm__ __volatile__ ( |
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"movec %/vbr,%2\n\t" |
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"movel #Lberr2,%4@(8)\n\t" |
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"movec %4,%/vbr\n\t" |
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"movel %/sp,%1\n\t" |
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"moveq #0,%0\n\t" |
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"movew %5,%3@\n\t" |
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"nop\n\t" |
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/* |
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* If this nop isn't present, 'ret' may already be loaded |
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* with 1 at the time the bus error happens! |
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*/ |
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"moveq #1,%0\n" |
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"Lberr2:\n\t" |
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"movel %1,%/sp\n\t" |
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"movec %2,%/vbr" |
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: "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr) |
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: "a" (regp), "a" (tmp_vectors), "g" (val) |
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); |
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local_irq_restore(flags); |
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return ret; |
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} |
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EXPORT_SYMBOL(hwreg_write); |
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