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ARM: 6188/1: Add a config option for the ARM11MPCore DMA cache maintenance workaround

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Commit f4d6477f introduced a workaround for the lack of hardware
broadcasting of the cache maintenance operations on ARM11MPCore.
However, the workaround is only valid on CPUs that do not do speculative
loads into the D-cache.

This patch adds a Kconfig option with the corresponding help to make the
above clear. When the DMA_CACHE_RWFO option is disabled, the kernel
behaviour is that prior to the f4d6477f commit. This also allows ARMv6
UP processors with speculative loads to work correctly.

For other processors, a different workaround may be needed.

Cc: Ronen Shitrit <rshitrit@marvell.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Catalin Marinas 2010-06-21 15:10:07 +01:00 committed by Russell King
parent ca57926d53
commit ad642d9f58
2 changed files with 31 additions and 3 deletions
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19
arch/arm/mm/Kconfig
View file

@ -735,6 +735,25 @@ config NEEDS_SYSCALL_FOR_CMPXCHG
Forget about fast user space cmpxchg support.
It is just not possible.
config DMA_CACHE_RWFO
bool "Enable read/write for ownership DMA cache maintenance"
depends on CPU_V6 && SMP
default y
help
The Snoop Control Unit on ARM11MPCore does not detect the
cache maintenance operations and the dma_{map,unmap}_area()
functions may leave stale cache entries on other CPUs. By
enabling this option, Read or Write For Ownership in the ARMv6
DMA cache maintenance functions is performed. These LDR/STR
instructions change the cache line state to shared or modified
so that the cache operation has the desired effect.
Note that the workaround is only valid on processors that do
not perform speculative loads into the D-cache. For such
processors, if cache maintenance operations are not broadcast
in hardware, other workarounds are needed (e.g. cache
maintenance broadcasting in software via FIQ).
config OUTER_CACHE
bool

15
arch/arm/mm/cache-v6.S
View file

@ -211,7 +211,7 @@ v6_dma_inv_range:
mcrne p15, 0, r1, c7, c15, 1 @ clean & invalidate unified line
#endif
1:
#ifdef CONFIG_SMP
#ifdef CONFIG_DMA_CACHE_RWFO
ldr r2, [r0] @ read for ownership
str r2, [r0] @ write for ownership
#endif
@ -235,7 +235,7 @@ v6_dma_inv_range:
v6_dma_clean_range:
bic r0, r0, #D_CACHE_LINE_SIZE - 1
1:
#ifdef CONFIG_SMP
#ifdef CONFIG_DMA_CACHE_RWFO
ldr r2, [r0] @ read for ownership
#endif
#ifdef HARVARD_CACHE
@ -258,7 +258,7 @@ v6_dma_clean_range:
ENTRY(v6_dma_flush_range)
bic r0, r0, #D_CACHE_LINE_SIZE - 1
1:
#ifdef CONFIG_SMP
#ifdef CONFIG_DMA_CACHE_RWFO
ldr r2, [r0] @ read for ownership
str r2, [r0] @ write for ownership
#endif
@ -284,9 +284,13 @@ ENTRY(v6_dma_map_area)
add r1, r1, r0
teq r2, #DMA_FROM_DEVICE
beq v6_dma_inv_range
#ifndef CONFIG_DMA_CACHE_RWFO
b v6_dma_clean_range
#else
teq r2, #DMA_TO_DEVICE
beq v6_dma_clean_range
b v6_dma_flush_range
#endif
ENDPROC(v6_dma_map_area)
/*
@ -296,6 +300,11 @@ ENDPROC(v6_dma_map_area)
* - dir - DMA direction
*/
ENTRY(v6_dma_unmap_area)
#ifndef CONFIG_DMA_CACHE_RWFO
add r1, r1, r0
teq r2, #DMA_TO_DEVICE
bne v6_dma_inv_range
#endif
mov pc, lr
ENDPROC(v6_dma_unmap_area)