ARM: 8559/1: errata: Workaround erratum A12 821420

This erratum has a very simple workaround (set a bit in a register), so
let's apply it.  Apparently the workaround's downside is a very slight
power impact.

Note that applying this errata fixes deadlocks that are easy to
reproduce with real world applications.

The arguments for why this needs to be in the kernel are similar to the
arugments made in the patch "Workaround errata A12 818325/852422 A17
852423".

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/proc-v7.S

@@ -367,6 +367,11 @@ __ca12_errata:
 	mrc	p15, 0, r10, c15, c0, 1		@ read diagnostic register
 	orr	r10, r10, #1 << 12		@ set bit #12
 	mcr	p15, 0, r10, c15, c0, 1		@ write diagnostic register
+#endif
+#ifdef CONFIG_ARM_ERRATA_821420
+	mrc	p15, 0, r10, c15, c0, 2		@ read internal feature reg
+	orr	r10, r10, #1 << 1		@ set bit #1
+	mcr	p15, 0, r10, c15, c0, 2		@ write internal feature reg
 #endif
 	b	__errata_finish