Provide a kconfig option to allow arches to manipulate default
value of dma_default_coherent in Kconfig.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 kernel/dma/Kconfig   | 3 +++
 kernel/dma/mapping.c | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index 56866aaa2ae1..968108fdf9bf 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -76,6 +76,9 @@ config ARCH_HAS_DMA_PREP_COHERENT
 config ARCH_HAS_FORCE_DMA_UNENCRYPTED
 	bool
 
+config ARCH_DMA_DEFAULT_COHERENT
+	bool
+
 config SWIOTLB
 	bool
 	select NEED_DMA_MAP_STATE
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index e0b005c8ffce..3d4a2ca15b5a 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -20,7 +20,7 @@
 #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
 	defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \
 	defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
-bool dma_default_coherent;
+bool dma_default_coherent = IS_ENABLED(CONFIG_ARCH_DMA_DEFAULT_COHERENT);
 #endif
 
 /*
-- 
2.37.1 (Apple Git-137.1)

On Tue, Feb 21, 2023 at 12:46:11PM +0000, Jiaxun Yang wrote:
> Provide a kconfig option to allow arches to manipulate default
> value of dma_default_coherent in Kconfig.

I don't see the win over just doing this by setting dma_default_coherent
in the early boot code.

> 2023年2月21日 17:58，Christoph Hellwig <hch@lst.de> 写道：
> 
> On Tue, Feb 21, 2023 at 12:46:11PM +0000, Jiaxun Yang wrote:
>> Provide a kconfig option to allow arches to manipulate default
>> value of dma_default_coherent in Kconfig.
> 
> I don't see the win over just doing this by setting dma_default_coherent
> in the early boot code.

I just don’t want to dig into every archs’ early boot code to decide a good
timing for setting this variable.

Also as we do have a OF_DMA_DEFAULT_COHERENT before it makes more
sense to me.

Thanks
- Jiaxun