[PATCH 02/25] dma-mapping: add a Kconfig symbol to indicated arch_dma_prep_coherent presence

[Christoph Hellwig <hch@lst.de>]

Add a Kconfig symbol that indicates an architecture provides a
arch_dma_prep_coherent implementation, and provide a stub otherwise.

This will allow the generic dma-iommu code to use it while still
allowing to be built for cache coherent architectures.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
---
 arch/arm64/Kconfig              | 1 +
 arch/csky/Kconfig               | 1 +
 include/linux/dma-noncoherent.h | 6 ++++++
 kernel/dma/Kconfig              | 3 +++
 4 files changed, 11 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7e34b9eba5de..adda078d6df7 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -13,6 +13,7 @@ config ARM64
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_DMA_COHERENT_TO_PFN
 	select ARCH_HAS_DMA_MMAP_PGPROT
+	select ARCH_HAS_DMA_PREP_COHERENT
 	select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FAST_MULTIPLIER
diff --git a/arch/csky/Kconfig b/arch/csky/Kconfig
index 725a115759c9..2c3178848b7d 100644
--- a/arch/csky/Kconfig
+++ b/arch/csky/Kconfig
@@ -1,6 +1,7 @@
 config CSKY
 	def_bool y
 	select ARCH_32BIT_OFF_T
+	select ARCH_HAS_DMA_PREP_COHERENT
 	select ARCH_HAS_SYNC_DMA_FOR_CPU
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 	select ARCH_USE_BUILTIN_BSWAP
diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
index 69b36ed31a99..9741767e400f 100644
--- a/include/linux/dma-noncoherent.h
+++ b/include/linux/dma-noncoherent.h
@@ -72,6 +72,12 @@ static inline void arch_sync_dma_for_cpu_all(struct device *dev)
 }
 #endif /* CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL */
 
+#ifdef CONFIG_ARCH_HAS_DMA_PREP_COHERENT
 void arch_dma_prep_coherent(struct page *page, size_t size);
+#else
+static inline void arch_dma_prep_coherent(struct page *page, size_t size)
+{
+}
+#endif /* CONFIG_ARCH_HAS_DMA_PREP_COHERENT */
 
 #endif /* _LINUX_DMA_NONCOHERENT_H */
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index 52b704e2b97a..83d711f8d665 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -38,6 +38,9 @@ config ARCH_HAS_SYNC_DMA_FOR_CPU
 config ARCH_HAS_SYNC_DMA_FOR_CPU_ALL
 	bool
 
+config ARCH_HAS_DMA_PREP_COHERENT
+	bool
+
 config ARCH_HAS_DMA_COHERENT_TO_PFN
 	bool
 
-- 
2.20.1