ARM: Introduce erratum workaround for 798870

Add workaround for Cortex-A15 ARM erratum 798870 which says
"If back-to-back speculative cache line fills (fill A and fill B) are
issued from the L1 data cache of a CPU to the L2 cache, the second
request (fill B) is then cancelled, and the second request would have
detected a hazard against a recent write or eviction (write B) to the
same cache line as fill B then the L2 logic might deadlock."

Implementations for SoC families such as Exynos, OMAP5/DRA7 etc
will be widely different.

Every SoC has slightly different manner of setting up access to L2ACLR
and similar registers since the Secure Monitor handling of Secure
Monitor Call(smc) is diverse. Hence an weak function is introduced
which may be overriden to implement SoC specific accessor implementation.

Based on ARM errata Document revision 18.0 (22 Nov 2013)

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

README

@@ -690,6 +690,11 @@ The following options need to be configured:
 		exists, unlike the similar options in the Linux kernel. Do not
 		set these options unless they apply!
 
+		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_798870
+
 - Tegra SoC options:
 		CONFIG_TEGRA_SUPPORT_NON_SECURE
 

arch/arm/cpu/armv7/Makefile

@@ -9,7 +9,7 @@ extra-y	:= start.o
 
 obj-y	+= cache_v7.o
 
-obj-y	+= cpu.o
+obj-y	+= cpu.o cp15.o
 obj-y	+= syslib.o
 
 ifneq ($(CONFIG_AM43XX)$(CONFIG_AM33XX)$(CONFIG_OMAP44XX)$(CONFIG_OMAP54XX)$(CONFIG_TEGRA)$(CONFIG_MX6)$(CONFIG_TI81XX)$(CONFIG_AT91FAMILY)$(CONFIG_SUNXI),)

arch/arm/cpu/armv7/cp15.c

@@ -0,0 +1,23 @@
+/*
+ * (C) Copyright 2015 Texas Insturments
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+/*
+ * CP15 specific code
+ */
+
+#include <common.h>
+#include <command.h>
+#include <asm/system.h>
+#include <asm/cache.h>
+#include <asm/armv7.h>
+#include <linux/compiler.h>
+
+void __weak v7_arch_cp15_set_l2aux_ctrl(u32 l2actlr, u32 cpu_midr,
+				     u32 cpu_rev_comb, u32 cpu_variant,
+				     u32 cpu_rev)
+{
+	asm volatile ("mcr p15, 1, %0, c15, c0, 0\n\t" : : "r"(l2actlr));
+}

arch/arm/cpu/armv7/start.S

@@ -166,7 +166,30 @@ ENTRY(cpu_init_cp15)
 	mcr	p15, 0, r0, c15, c0, 1	@ write diagnostic register
 #endif
 
-	mov	pc, lr			@ back to my caller
+	mov	r5, lr			@ Store my Caller
+	mrc	p15, 0, r1, c0, c0, 0	@ r1 has Read Main ID Register (MIDR)
+	mov	r3, r1, lsr #20		@ get variant field
+	and	r3, r3, #0xf		@ r3 has CPU variant
+	and	r4, r1, #0xf		@ r4 has CPU revision
+	mov	r2, r3, lsl #4		@ shift variant field for combined value
+	orr	r2, r4, r2		@ r2 has combined CPU variant + revision
+
+#ifdef CONFIG_ARM_ERRATA_798870
+	cmp	r2, #0x30		@ Applies to lower than R3p0
+	bge	skip_errata_798870      @ skip if not affected rev
+	cmp	r2, #0x20		@ Applies to including and above R2p0
+	blt	skip_errata_798870      @ skip if not affected rev
+
+	mrc	p15, 1, r0, c15, c0, 0  @ read l2 aux ctrl reg
+	orr	r0, r0, #1 << 7         @ Enable hazard-detect timeout
+	push	{r1-r5}			@ Save the cpu info registers
+	bl	v7_arch_cp15_set_l2aux_ctrl
+	isb				@ Recommended ISB after l2actlr update
+	pop	{r1-r5}			@ Restore the cpu info - fall through
+skip_errata_798870:
+#endif
+
+	mov	pc, r5			@ back to my caller
 ENDPROC(cpu_init_cp15)
 
 #ifndef CONFIG_SKIP_LOWLEVEL_INIT

arch/arm/include/asm/armv7.h

@@ -137,6 +137,9 @@ extern char __secure_end[];
 
 #endif /* CONFIG_ARMV7_NONSEC || CONFIG_ARMV7_VIRT */
 
+void v7_arch_cp15_set_l2aux_ctrl(u32 l2auxctrl, u32 cpu_midr,
+				 u32 cpu_rev_comb, u32 cpu_variant,
+				 u32 cpu_rev);
 #endif /* ! __ASSEMBLY__ */
 
 #endif