MIPS: improve checks for noncoherent DMA

Only one MIPS development board actually supports enabling/disabling DMA
coherency at runtime, so it's not a good idea to push the overhead of
checking that configuration setting onto every other supported target as
well.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/5912/

4 files changed, 16 insertions, 5 deletions

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index a7ec153be0b9..57a887334a65 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -301,7 +301,7 @@ config MIPS_MALTA
         select CEVT_R4K
         select CSRC_R4K
         select CSRC_GIC
-        select DMA_NONCOHERENT
+        select DMA_MAYBE_COHERENT
         select GENERIC_ISA_DMA
         select HAVE_PCSPKR_PLATFORM
         select IRQ_CPU
@@ -893,6 +893,10 @@ config FW_CFE
 config ARCH_DMA_ADDR_T_64BIT
         def_bool (HIGHMEM && 64BIT_PHYS_ADDR) || 64BIT
 
+config DMA_MAYBE_COHERENT
+        select DMA_NONCOHERENT
+        bool
+
 config DMA_COHERENT
         bool
 
diff --git a/arch/mips/include/asm/dma-coherence.h b/arch/mips/include/asm/dma-coherence.h
index 242cbb3ca582..bc5e85d579e6 100644
--- a/arch/mips/include/asm/dma-coherence.h
+++ b/arch/mips/include/asm/dma-coherence.h
@@ -9,7 +9,16 @@
 #ifndef __ASM_DMA_COHERENCE_H
 #define __ASM_DMA_COHERENCE_H
 
+#ifdef CONFIG_DMA_MAYBE_COHERENT
 extern int coherentio;
 extern int hw_coherentio;
+#else
+#ifdef CONFIG_DMA_COHERENT
+#define coherentio      1
+#else
+#define coherentio      0
+#endif
+#define hw_coherentio   0
+#endif /* CONFIG_DMA_MAYBE_COHERENT */
 
 #endif
diff --git a/arch/mips/include/asm/mach-generic/dma-coherence.h b/arch/mips/include/asm/mach-generic/dma-coherence.h
index a9e8f6b62b0b..7629c35986f7 100644
--- a/arch/mips/include/asm/mach-generic/dma-coherence.h
+++ b/arch/mips/include/asm/mach-generic/dma-coherence.h
@@ -49,11 +49,7 @@ static inline int plat_dma_supported(struct device *dev, u64 mask)
 
 static inline int plat_device_is_coherent(struct device *dev)
 {
-#ifdef CONFIG_DMA_COHERENT
-        return 1;
-#else
         return coherentio;
-#endif
 }
 
 #ifdef CONFIG_SWIOTLB
diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
index 2e9418562258..44b6dff5aba2 100644
--- a/arch/mips/mm/dma-default.c
+++ b/arch/mips/mm/dma-default.c
@@ -23,6 +23,7 @@
 
 #include <dma-coherence.h>
 
+#ifdef CONFIG_DMA_MAYBE_COHERENT
 int coherentio = 0;     /* User defined DMA coherency from command line. */
 EXPORT_SYMBOL_GPL(coherentio);
 int hw_coherentio = 0;  /* Actual hardware supported DMA coherency setting. */
@@ -42,6 +43,7 @@ static int __init setnocoherentio(char *str)
         return 0;
 }
 early_param("nocoherentio", setnocoherentio);
+#endif
 
 static inline struct page *dma_addr_to_page(struct device *dev,
         dma_addr_t dma_addr)