MIPS: Document why RELOC_HIDE is there.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/page.h

@@ -150,6 +150,20 @@ typedef struct { unsigned long pgprot; } pgprot_t;
     ((unsigned long)(x) - PAGE_OFFSET + PHYS_OFFSET)
 #endif
 #define __va(x)		((void *)((unsigned long)(x) + PAGE_OFFSET - PHYS_OFFSET))
+
+/*
+ * RELOC_HIDE was originally added by 6007b903dfe5f1d13e0c711ac2894bdd4a61b1ad
+ * (lmo) rsp. 8431fd094d625b94d364fe393076ccef88e6ce18 (kernel.org).  The
+ * discussion can be found in lkml posting
+ * <a2ebde260608230500o3407b108hc03debb9da6e62c@mail.gmail.com> which is
+ * archived at http://lists.linuxcoding.com/kernel/2006-q3/msg17360.html
+ *
+ * It is unclear if the misscompilations mentioned in
+ * http://lkml.org/lkml/2010/8/8/138 also affect MIPS so we keep this one
+ * until GCC 3.x has been retired before we can apply
+ * https://patchwork.linux-mips.org/patch/1541/
+ */
+
 #define __pa_symbol(x)	__pa(RELOC_HIDE((unsigned long)(x), 0))
 
 #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)