ARC: [Review] Multi-platform image imx6-dongle#6: cpu-to-dma-addr opt…

…ional

All the current platforms can work with 0x8000_0000 based dma_addr_t
since the Bus Bridges typically ignore the top bit (the only excpetion
was Angel4 PCI-AHB bridge which we no longer care for).
That way we don't need plat-specific cpu-addr to bus-addr conversion.

Hooks still provided - just in case a platform has an obscure device
which say needs 0 based bus address.

That way <asm/dma_mapping.h> no longer needs to unconditinally include
<plat/dma_addr.h>

Also verfied that on Angel4 board, other peripherals (IDE-disk / EMAC)
work fine with 0x8000_0000 based dma addresses.

Signed-off-by: Vineet Gupta <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>

arch/arc/Kconfig

@@ -119,6 +119,10 @@ config CPU_BIG_ENDIAN
 	help
 	  Build kernel for Big Endian Mode of ARC CPU
 
+# If a platform can't work with 0x8000_0000 based dma_addr_t
+config ARC_PLAT_NEEDS_CPU_TO_DMA
+	bool
+
 config SMP
 	bool "Symmetric Multi-Processing (Incomplete)"
 	default n

arch/arc/include/asm/dma-mapping.h

@@ -13,7 +13,23 @@
 
 #include <asm-generic/dma-coherent.h>
 #include <asm/cacheflush.h>
+
+#ifndef CONFIG_ARC_PLAT_NEEDS_CPU_TO_DMA
+/*
+ * dma_map_* API take cpu addresses, which is kernel logical address in the
+ * untranslated address space (0x8000_0000) based. The dma address (bus addr)
+ * ideally needs to be 0x0000_0000 based hence these glue routines.
+ * However given that intermediate bus bridges can ignore the high bit, we can
+ * do with these routines being no-ops.
+ * If a platform/device comes up which sriclty requires 0 based bus addr
+ * (e.g. AHB-PCI bridge on Angel4 board), then it can provide it's own versions
+ */
+#define plat_dma_addr_to_kernel(dev, addr) ((unsigned long)(addr))
+#define plat_kernel_addr_to_dma(dev, ptr) ((dma_addr_t)(ptr))
+
+#else
 #include <plat/dma_addr.h>
+#endif
 
 void *dma_alloc_noncoherent(struct device *dev, size_t size,
 			    dma_addr_t *dma_handle, gfp_t gfp);