On Thu, Jun 27, 2002 at 02:21:30PM +0200, Maciej W. Rozycki wrote:

On Wed, 26 Jun 2002, Ladislav Michl wrote:

quoted

+int be_ip22_handler(struct pt_regs *regs, int is_fixup)
+{
+	save_and_clear_buserr();
+	if (nofault) {
+		nofault = 0;
+		compute_return_epc(regs);
+		return MIPS_BE_DISCARD;
+	}
+	return MIPS_BE_FIXUP;
+}

 I wouldn't use nofault -- it leads to reentrancy problems and I don't
think you really need it.  You probably need to code it like this:

{
	save_and_clear_buserr();

	return is_fixup ? MIPS_BE_FIXUP : MIPS_BE_FATAL;
}

unless:

1. There is a condition when for is_fixup true you should ignore the fixup
anyway (e.g. what the bus error logic reports is irrelevant to fixups). 
You should choose between MIPS_BE_FATAL and MIPS_BE_DISCARD then. 

2. There is a condition when for is_fixup false, an error is not fatal and
execution should get restarted.  You should return MIPS_BE_DISCARD then.

There are no such conditions (or I'm missing something). I wrote it as
you suggested:

int be_ip22_handler(struct pt_regs *regs, int is_fixup)
{
  DBG("BE exception (%s)\n", is_fixup ? "fixup" : "no fixup");
  save_and_clear_buserr();
  if (is_fixup)
    return MIPS_BE_FIXUP;
  print_buserr();
  return MIPS_BE_FATAL;
}

try to read status register

  addr = KSEG1ADDR(gio_slot_base_addr);
  DBG("get_dbe\n");
  if (!get_dbe(id, addr)) {
    ... ok
  }							

quoted

+int ip22_baddr(unsigned int *val, unsigned long addr)
+{
+	nofault = 1;
+	*val = *(volatile unsigned int *) addr;
+	__asm__ __volatile__("nop;nop;nop;nop");
+	if (nofault) {
+		nofault = 0;
+		return 0;
+	}
+	return -EFAULT;
+}

 Why not simply:

{
	int err;

	err = get_dbe(*val, (volatile unsigned int *) addr);

	return err ? -EFAULT : 0;
}

It was designed exactly for this purpose.  You may consider using "u32" 
instead of "unsigned int" for hardware accesses to assure the type will
always be 32-bit.

This way gives following result:

get_dbe
BE exception (no fixup)

Dump of MC registers shows that timeout occurs when accessing nonexistant
memory. Of course it is posible return MIPS_BE_DISCARD than (and
regs->cp0_epc += 4), but how to force get_dbe fail then? Not mentioning
that in such case is better to avoid use of get_dbe... Suggestions are
welcome as always.

Thanks a lot,
	Ladis