ARM: relax ioremap prohibition (309caa9c) for -final and -stable

... but produce a big warning about the problem as encouragement
for people to fix their drivers.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/ioremap.c

@@ -204,8 +204,12 @@ void __iomem * __arm_ioremap_pfn_caller(unsigned long pfn,
 	/*
 	 * Don't allow RAM to be mapped - this causes problems with ARMv6+
 	 */
-	if (WARN_ON(pfn_valid(pfn)))
-		return NULL;
+	if (pfn_valid(pfn)) {
+		printk(KERN_WARNING "BUG: Your driver calls ioremap() on system memory.  This leads\n"
+		       KERN_WARNING "to architecturally unpredictable behaviour on ARMv6+, and ioremap()\n"
+		       KERN_WARNING "will fail in the next kernel release.  Please fix your driver.\n");
+		WARN_ON(1);
+	}
 
 	type = get_mem_type(mtype);
 	if (!type)