ARM: Introduce erratum workaround for 454179

454179: Stale prediction may inhibit target address misprediction on
	next predicted taken branch
Impacts: Every Cortex-A8 processors with revision lower than r2p1
Work around:  Set IBE and disable branch size mispredict to 1

Also provide a hook for SoC specific handling to take place if needed.

Based on ARM errata Document revision 20.0 (13 Nov 2010)

Signed-off-by: Nishanth Menon <nm@ti.com>
Tested-by: Matt Porter <mporter@konsulko.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

README

@@ -693,6 +693,7 @@ The following options need to be configured:
 		NOTE: The following can be machine specific errata. These
 		do have ability to provide rudimentary version and machine
 		specific checks, but expect no product checks.
+		CONFIG_ARM_ERRATA_454179
 		CONFIG_ARM_ERRATA_798870
 
 - Tegra SoC options:

arch/arm/cpu/armv7/cp15.c

@@ -21,3 +21,9 @@ void __weak v7_arch_cp15_set_l2aux_ctrl(u32 l2actlr, u32 cpu_midr,
 {
 	asm volatile ("mcr p15, 1, %0, c15, c0, 0\n\t" : : "r"(l2actlr));
 }
+
+void __weak v7_arch_cp15_set_acr(u32 acr, u32 cpu_midr, u32 cpu_rev_comb,
+				 u32 cpu_variant, u32 cpu_rev)
+{
+	asm volatile ("mcr p15, 0, %0, c1, c0, 1\n\t" : : "r"(acr));
+}

arch/arm/cpu/armv7/start.S

@@ -187,6 +187,19 @@ ENTRY(cpu_init_cp15)
 	isb				@ Recommended ISB after l2actlr update
 	pop	{r1-r5}			@ Restore the cpu info - fall through
 skip_errata_798870:
+#endif
+
+#ifdef CONFIG_ARM_ERRATA_454179
+	cmp	r2, #0x21		@ Only on < r2p1
+	bge	skip_errata_454179
+
+	mrc	p15, 0, r0, c1, c0, 1	@ Read ACR
+	orr	r0, r0, #(0x3 << 6)	@ Set DBSM(BIT7) and IBE(BIT6) bits
+	push	{r1-r5}			@ Save the cpu info registers
+	bl	v7_arch_cp15_set_acr
+	pop	{r1-r5}			@ Restore the cpu info - fall through
+
+skip_errata_454179:
 #endif
 
 	mov	pc, r5			@ back to my caller

arch/arm/include/asm/armv7.h

@@ -140,6 +140,8 @@ extern char __secure_end[];
 void v7_arch_cp15_set_l2aux_ctrl(u32 l2auxctrl, u32 cpu_midr,
 				 u32 cpu_rev_comb, u32 cpu_variant,
 				 u32 cpu_rev);
+void v7_arch_cp15_set_acr(u32 acr, u32 cpu_midr, u32 cpu_rev_comb,
+			  u32 cpu_variant, u32 cpu_rev);
 #endif /* ! __ASSEMBLY__ */
 
 #endif