ARM: 6388/1: errata: DMB operation may be faulty

On versions of the Cortex-A9 up to and including r2p2, under rare
circumstances, a DMB instruction between 2 write operations may not
ensure the correct visibility ordering of the 2 writes.

This workaround sets a bit in the diagnostic register of the Cortex-A9,
causing the DMB instruction to behave like a DSB, which functions
correctly on the affected cores.

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>

2 files changed, 26 insertions, 2 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 553b7cf17bfb..ab14c0a5d21e 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1051,6 +1051,18 @@ config ARM_ERRATA_460075
           ACTLR register. Note that setting specific bits in the ACTLR register
           may not be available in non-secure mode.
 
+config ARM_ERRATA_742230
+        bool "ARM errata: DMB operation may be faulty"
+        depends on CPU_V7 && SMP
+        help
+          This option enables the workaround for the 742230 Cortex-A9
+          (r1p0..r2p2) erratum. Under rare circumstances, a DMB instruction
+          between two write operations may not ensure the correct visibility
+          ordering of the two writes. This workaround sets a specific bit in
+          the diagnostic register of the Cortex-A9 which causes the DMB
+          instruction to behave as a DSB, ensuring the correct behaviour of
+          the two writes.
+
 config PL310_ERRATA_588369
         bool "Clean & Invalidate maintenance operations do not invalidate clean lines"
         depends on CACHE_L2X0 && ARCH_OMAP4
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 1f16f9e3f441..945f36341fa6 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -201,7 +201,7 @@ __v7_setup:
         mrc     p15, 0, r0, c0, c0, 0           @ read main ID register
         and     r10, r0, #0xff000000            @ ARM?
         teq     r10, #0x41000000
-        bne     2f
+        bne     3f
         and     r5, r0, #0x00f00000             @ variant
         and     r6, r0, #0x0000000f             @ revision
         orr     r6, r6, r5, lsr #20-4           @ combine variant and revision
@@ -231,8 +231,20 @@ __v7_setup:
         orreq   r10, r10, #(1 << 22)            @ set the Write Allocate disable bit
         mcreq   p15, 1, r10, c9, c0, 2          @ write the L2 cache aux ctrl register
 #endif
+        b       3f
+
+        /* Cortex-A9 Errata */
+2:      ldr     r10, =0x00000c09                @ Cortex-A9 primary part number
+        teq     r0, r10
+        bne     3f
+#ifdef CONFIG_ARM_ERRATA_742230
+        cmp     r6, #0x22                       @ only present up to r2p2
+        mrcle   p15, 0, r10, c15, c0, 1         @ read diagnostic register
+        orrle   r10, r10, #1 << 4               @ set bit #4
+        mcrle   p15, 0, r10, c15, c0, 1         @ write diagnostic register
+#endif
 
-2:      mov     r10, #0
+3:      mov     r10, #0
 #ifdef HARVARD_CACHE
         mcr     p15, 0, r10, c7, c5, 0          @ I+BTB cache invalidate
 #endif