[PATCH] IPMI: fix for handling bad ACPI data

If the ACPI register bit width is zero (an invalid value) assume it is the
default spacing.  This avoids some coredumps on invalid data and makes some
systems work that have broken ACPI data.
Signed-off-by: Corey Minyard <minyard@acm.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/char/ipmi/ipmi_si_intf.c

@@ -1526,8 +1526,17 @@ static int try_init_acpi(int intf_num, struct smi_info **new_info)
 		info->irq_setup = NULL;
 	}
 
-	regspacings[intf_num] = spmi->addr.register_bit_width / 8;
-	info->io.regspacing = spmi->addr.register_bit_width / 8;
+	if (spmi->addr.register_bit_width) {
+		/* A (hopefully) properly formed register bit width. */
+		regspacings[intf_num] = spmi->addr.register_bit_width / 8;
+		info->io.regspacing = spmi->addr.register_bit_width / 8;
+	} else {
+		/* Some broken systems get this wrong and set the value
+		 * to zero.  Assume it is the default spacing.  If that
+		 * is wrong, too bad, the vendor should fix the tables. */
+		regspacings[intf_num] = DEFAULT_REGSPACING;
+		info->io.regspacing = DEFAULT_REGSPACING;
+	}
 	regsizes[intf_num] = regspacings[intf_num];
 	info->io.regsize = regsizes[intf_num];
 	regshifts[intf_num] = spmi->addr.register_bit_offset;