/* 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 , 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 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); private-remove'>arm/xen

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