dma-mapping: provide a fallback dma_default_coherent

dma_default_coherent was decleared unconditionally at kernel/dma/mapping.c
but only decleared when any of non-coherent options is enabled in
dma-map-ops.h.

Guard the declaration in mapping.c with non-coherent options and provide
a fallback definition.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

include/linux/dma-map-ops.h

@@ -269,6 +269,8 @@ static inline bool dev_is_dma_coherent(struct device *dev)
 	return dev->dma_coherent;
 }
 #else
+#define dma_default_coherent true
+
 static inline bool dev_is_dma_coherent(struct device *dev)
 {
 	return true;

kernel/dma/mapping.c

@@ -17,7 +17,11 @@
 #include "debug.h"
 #include "direct.h"
 
+#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;
+#endif
 
 /*
  * Managed DMA API