drivers/edac/i3000: document type promotion

By popular request, add a comment documenting the implicit type promotion
here.
Signed-off-by: Jason Uhlenkott <juhlenko@akamai.com>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/edac/i3000_edac.c

@@ -44,6 +44,13 @@
 				 */
 #define I3000_DEAP_GRAIN 		(1 << 7)
 
+/*
+ * Helper functions to decode the DEAP/EDEAP hardware registers.
+ *
+ * The type promotion here is deliberate; we're deriving an
+ * unsigned long pfn and offset from hardware regs which are u8/u32.
+ */
+
 static inline unsigned long deap_pfn(u8 edeap, u32 deap)
 {
 	deap >>= PAGE_SHIFT;