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[6/7] ARM: NOMMU: Set ARM_DMA_MEM_BUFFERABLE for M-class cpus

Message ID 1487152792-34214-7-git-send-email-vladimir.murzin@arm.com
State New, archived
Headers show

Commit Message

Vladimir Murzin Feb. 15, 2017, 9:59 a.m. UTC
Now, we have dedicated non-cacheable region for consistent DMA
operations. However, that region can still be marked as bufferable by
MPU, so it'd be safer to have barriers by default.

Tested-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Tested-by: Andras Szemzo <sza@esh.hu>
Tested-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
---
 arch/arm/mm/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Robin Murphy Feb. 21, 2017, 12:57 p.m. UTC | #1
On 15/02/17 09:59, Vladimir Murzin wrote:
> Now, we have dedicated non-cacheable region for consistent DMA
> operations. However, that region can still be marked as bufferable by
> MPU, so it'd be safer to have barriers by default.

Makes sense - plenty of cases want their DMA buffers to still be
write-combining (e.g. framebuffers have already been mentioned here),
for which strongly-ordered mappings won't do. Plus you don't exactly
have a choice if you've no MPU and have fixed Normal attributes for your
RAM region.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Tested-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> Tested-by: Andras Szemzo <sza@esh.hu>
> Tested-by: Alexandre TORGUE <alexandre.torgue@st.com>
> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
> ---
>  arch/arm/mm/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
> index 0b79f12..64a1465c 100644
> --- a/arch/arm/mm/Kconfig
> +++ b/arch/arm/mm/Kconfig
> @@ -1029,7 +1029,7 @@ config ARM_L1_CACHE_SHIFT
>  
>  config ARM_DMA_MEM_BUFFERABLE
>  	bool "Use non-cacheable memory for DMA" if (CPU_V6 || CPU_V6K) && !CPU_V7
> -	default y if CPU_V6 || CPU_V6K || CPU_V7
> +	default y if CPU_V6 || CPU_V6K || CPU_V7 || CPU_V7M
>  	help
>  	  Historically, the kernel has used strongly ordered mappings to
>  	  provide DMA coherent memory.  With the advent of ARMv7, mapping
>
Vladimir Murzin Feb. 21, 2017, 1:03 p.m. UTC | #2
On 21/02/17 12:57, Robin Murphy wrote:
> On 15/02/17 09:59, Vladimir Murzin wrote:
>> Now, we have dedicated non-cacheable region for consistent DMA
>> operations. However, that region can still be marked as bufferable by
>> MPU, so it'd be safer to have barriers by default.
> 
> Makes sense - plenty of cases want their DMA buffers to still be
> write-combining (e.g. framebuffers have already been mentioned here),
> for which strongly-ordered mappings won't do. Plus you don't exactly
> have a choice if you've no MPU and have fixed Normal attributes for your
> RAM region.
> 
> Reviewed-by: Robin Murphy <robin.murphy@arm.com>

Thanks!

Vladimir

> 
>> Tested-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
>> Tested-by: Andras Szemzo <sza@esh.hu>
>> Tested-by: Alexandre TORGUE <alexandre.torgue@st.com>
>> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
>> ---
>>  arch/arm/mm/Kconfig | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
>> index 0b79f12..64a1465c 100644
>> --- a/arch/arm/mm/Kconfig
>> +++ b/arch/arm/mm/Kconfig
>> @@ -1029,7 +1029,7 @@ config ARM_L1_CACHE_SHIFT
>>  
>>  config ARM_DMA_MEM_BUFFERABLE
>>  	bool "Use non-cacheable memory for DMA" if (CPU_V6 || CPU_V6K) && !CPU_V7
>> -	default y if CPU_V6 || CPU_V6K || CPU_V7
>> +	default y if CPU_V6 || CPU_V6K || CPU_V7 || CPU_V7M
>>  	help
>>  	  Historically, the kernel has used strongly ordered mappings to
>>  	  provide DMA coherent memory.  With the advent of ARMv7, mapping
>>
> 
>
diff mbox

Patch

diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 0b79f12..64a1465c 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -1029,7 +1029,7 @@  config ARM_L1_CACHE_SHIFT
 
 config ARM_DMA_MEM_BUFFERABLE
 	bool "Use non-cacheable memory for DMA" if (CPU_V6 || CPU_V6K) && !CPU_V7
-	default y if CPU_V6 || CPU_V6K || CPU_V7
+	default y if CPU_V6 || CPU_V6K || CPU_V7 || CPU_V7M
 	help
 	  Historically, the kernel has used strongly ordered mappings to
 	  provide DMA coherent memory.  With the advent of ARMv7, mapping