Enable partial low interrupt latency mode for ARM1136

This patch is a workaround for the 364296 ARM1136 r0pX errata
(possible cache data corruption with hit-under-miss enabled). It sets
the undocumented bit 31 in the auxiliary control register and the FI bit in
the control register, thus disabling hit-under-miss without putting the
processor into full low interrupt latency mode.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm/Kconfig

@@ -514,6 +514,19 @@ if !MMU
 source "arch/arm/Kconfig-nommu"
 endif
 
+config ARM_ERRATA_364296
+	bool "Enable partial low interrupt latency mode for ARM1136"
+	depends on CPU_V6 && !SMP
+	default n
+	help
+	  This options enables the workaround for the 364296 ARM1136
+	  r0pX errata (possible cache data corruption with
+	  hit-under-miss enabled). It sets the undocumented bit 31 in
+	  the auxiliary control register and the FI bit in the control
+	  register, thus disabling hit-under-miss without putting the
+	  processor into full low interrupt latency mode. ARM11MPCore
+	  is not affected.
+
 endmenu
 
 source "arch/arm/common/Kconfig"

arch/arm/mm/proc-v6.S

@@ -204,6 +204,22 @@ __v6_setup:
 	mrc	p15, 0, r0, c1, c0, 0		@ read control register
 	bic	r0, r0, r5			@ clear bits them
 	orr	r0, r0, r6			@ set them
+#ifdef CONFIG_ARM_ERRATA_364296
+	/* Workaround for the 364296 ARM1136 r0pX errata (possible cache data
+	 * corruption with hit-under-miss enabled). The conditional code below
+	 * (setting the undocumented bit 31 in the auxiliary control register
+	 * and the FI bit in the control register) disables hit-under-miss
+	 * without putting the processor into full low interrupt latency mode.
+	 */
+	ldr	r6, =0x4107b360			@ id for ARM1136 r0pX
+	mrc	p15, 0, r5, c0, c0, 0		@ get processor id
+	bic	r5, r5, #0xf			@ mask out part bits [3:0]
+	teq	r5, r6				@ check for the faulty core
+	mrceq	p15, 0, r5, c1, c0, 1		@ load aux control reg
+	orreq	r5, r5, #(1 << 31)		@ set the undocumented bit 31
+	mcreq	p15, 0, r5, c1, c0, 1		@ write aux control reg
+	orreq	r0, r0, #(1 << 21)		@ low interrupt latency configuration
+#endif
 	mov	pc, lr				@ return to head.S:__ret
 
 	/*