[PATCH v2 1/4] ARM: cache-armv7: work around Cortex-A7 erratum 814220

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

This patch is based on 0e9a87bb from the linux-imx kernel:
------------------------------------------------------------------------------
| ARM/MP: 814220—B-Cache maintenance by set/way operations can execute
| 	out of order.
|
| Description:
| The v7 ARM states that all cache and branch predictor maintenance operations
| that do not specify an address execute, relative to each other, in program
| order. However, because of this erratum, an L2 set/way cache maintenance
| operation can overtake an L1 set/way cache maintenance operation, this would
| cause the data corruption.
|
| This ERRATA affected the Cortex-A7 and present in r0p2, r0p3, r0p4, r0p5.
|
| This patch is the SW workaround by adding a DSB before changing cache levels
| as the ARM ERRATA: ARM/MP: 814220 told in the ARM ERRATA documentation.
| Signed-off-by: Jason Liu <r64343@freescale.com>
------------------------------------------------------------------------------

It was later posted to LKML for Linux inclusion, but is not yet mainline:
<20190214083145.15148-1-benjamin.gaignard@linaro.org>

Unlike the Linux version, we don't make the barrier dependent on a
Kconfig option and always execute the dsb:

On 25/4/19 12:02, Lucas Stach wrote:
> I don't think we need a Kconfig option here. This function is not
> really performance critical. The short pipeline stall introduced by the
> dsb when switching the cache level is minor compared to the time it
> takes to actually move the cache blocks on a clean.
>
> Just always execute the [dsb] and add a comment on why it is needed.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 arch/arm/cpu/cache-armv7.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/cpu/cache-armv7.S b/arch/arm/cpu/cache-armv7.S
index 7a1c5c01894c..9487dd03f6cc 100644
--- a/arch/arm/cpu/cache-armv7.S
+++ b/arch/arm/cpu/cache-armv7.S
@@ -120,6 +120,7 @@ THUMB(		ite	eq			)
 skip:
 		add	r12, r12, #2		@ increment cache number
 		cmp	r3, r12
+		dsb				@ work-around Cortex-A7 erratum 814220
 		bgt	loop1
 finished:
 		ldmfd	sp!, {r4-r11}
-- 
2.20.1


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