ppc32: Add a 'noresidual' option, to ignore residual data.

Signed-off-by: Leigh Brown <leigh@solinno.co.uk>
Signed-off-by: Tom Rini <trini@kernel.crashing.org>

Documentation/kernel-parameters.txt

@@ -741,6 +741,8 @@ running once the system is up.
 
 	nomce		[IA-32] Machine Check Exception
 
+	noresidual	[PPC] Don't use residual data on PReP machines.
+
 	noresume	[SWSUSP] Disables resume and restore original swap space.
  
 	no-scroll	[VGA] Disables scrollback.

arch/ppc/Kconfig

@@ -832,10 +832,11 @@ config PREP_RESIDUAL
 	  Some PReP systems have residual data passed to the kernel by the
 	  firmware.  This allows detection of memory size, devices present and
 	  other useful pieces of information.  Sometimes this information is
-	  not present or incorrect.
+	  not present or incorrect, in which case it could lead to the machine 
+	  behaving incorrectly.  If this happens, either disable PREP_RESIDUAL
+	  or pass the 'noresidual' option to the kernel.
 
-	  Unless you expect to boot on a PReP system, there is no need to
-	  select Y.
+	  If you are running a PReP system, say Y here, otherwise say N.
 
 config PROC_PREPRESIDUAL
 	bool "Support for reading of PReP Residual Data in /proc"

arch/ppc/platforms/prep_setup.c

@@ -1126,6 +1126,10 @@ prep_init(unsigned long r3, unsigned long r4, unsigned long r5,
 		_prep_type = _PREP_Motorola;
 	}
 
+	/* Switch off all residual data processing if the user requests it */
+	if (strstr(cmd_line, "noresidual") != NULL)
+			res = NULL;
+
 	/* Initialise progress early to get maximum benefit */
 	prep_set_bat();
 	ibm_statusled_init();