ARM: 7823/1: errata: workaround Cortex-A15 erratum 773022

On Cortex-A15 CPUs up to and including r0p4, in certain rare sequences
of code, the loop buffer may deliver incorrect instructions. This
workaround disables the loop buffer to avoid the erratum.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/Kconfig

@@ -1373,6 +1373,15 @@ config ARM_ERRATA_798181
 	  which sends an IPI to the CPUs that are running the same ASID
 	  as the one being invalidated.
 
+config ARM_ERRATA_773022
+	bool "ARM errata: incorrect instructions may be executed from loop buffer"
+	depends on CPU_V7
+	help
+	  This option enables the workaround for the 773022 Cortex-A15
+	  (up to r0p4) erratum. In certain rare sequences of code, the
+	  loop buffer may deliver incorrect instructions. This
+	  workaround disables the loop buffer to avoid the erratum.
+
 endmenu
 
 source "arch/arm/common/Kconfig"

arch/arm/mm/proc-v7.S

@@ -329,7 +329,19 @@ __v7_setup:
 1:
 #endif
 
-3:	mov	r10, #0
+	/* Cortex-A15 Errata */
+3:	ldr	r10, =0x00000c0f		@ Cortex-A15 primary part number
+	teq	r0, r10
+	bne	4f
+
+#ifdef CONFIG_ARM_ERRATA_773022
+	cmp	r6, #0x4			@ only present up to r0p4
+	mrcle	p15, 0, r10, c1, c0, 1		@ read aux control register
+	orrle	r10, r10, #1 << 1		@ disable loop buffer
+	mcrle	p15, 0, r10, c1, c0, 1		@ write aux control register
+#endif
+
+4:	mov	r10, #0
 	mcr	p15, 0, r10, c7, c5, 0		@ I+BTB cache invalidate
 	dsb
 #ifdef CONFIG_MMU