ARM: 6416/1: errata: faulty hazard checking in the Store Buffer may lead to data corruption

On the r2p0, r2p1 and r2p2 versions of the Cortex-A9, data corruption
can occur under very rare conditions due to a store buffer optimisation.

This workaround sets a bit in the diagnostic register of the Cortex-A9,
disabling the optimisation and preventing the problem from occurring.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/Kconfig

@@ -1101,6 +1101,20 @@ config ARM_ERRATA_720789
 	  invalidated are not, resulting in an incoherency in the system page
 	  tables. The workaround changes the TLB flushing routines to invalidate
 	  entries regardless of the ASID.
+
+config ARM_ERRATA_743622
+	bool "ARM errata: Faulty hazard checking in the Store Buffer may lead to data corruption"
+	depends on CPU_V7
+	help
+	  This option enables the workaround for the 743622 Cortex-A9
+	  (r2p0..r2p2) erratum. Under very rare conditions, a faulty
+	  optimisation in the Cortex-A9 Store Buffer may lead to data
+	  corruption. This workaround sets a specific bit in the diagnostic
+	  register of the Cortex-A9 which disables the Store Buffer
+	  optimisation, preventing the defect from occurring. This has no
+	  visible impact on the overall performance or power consumption of the
+	  processor.
+
 endmenu
 
 source "arch/arm/common/Kconfig"

arch/arm/mm/proc-v7.S

@@ -253,6 +253,14 @@ __v7_setup:
 	orreq	r10, r10, #1 << 22		@ set bit #22
 	mcreq	p15, 0, r10, c15, c0, 1		@ write diagnostic register
 #endif
+#ifdef CONFIG_ARM_ERRATA_743622
+	teq	r6, #0x20			@ present in r2p0
+	teqne	r6, #0x21			@ present in r2p1
+	teqne	r6, #0x22			@ present in r2p2
+	mrceq	p15, 0, r10, c15, c0, 1		@ read diagnostic register
+	orreq	r10, r10, #1 << 6		@ set bit #6
+	mcreq	p15, 0, r10, c15, c0, 1		@ write diagnostic register
+#endif
 
 3:	mov	r10, #0
 #ifdef HARVARD_CACHE