x86: provide a bad_dma_address symbol for i386

It's initially 0, since we don't expect any DMA there.
Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/pci-dma_32.c

@@ -14,6 +14,10 @@
 #include <linux/module.h>
 #include <asm/io.h>
 
+/* For i386, we make it point to the NULL address */
+dma_addr_t bad_dma_address __read_mostly = 0x0;
+EXPORT_SYMBOL(bad_dma_address);
+
 struct dma_coherent_mem {
 	void		*virt_base;
 	u32		device_base;

include/asm-x86/dma-mapping.h

@@ -10,6 +10,8 @@
 #include <asm/io.h>
 #include <asm/swiotlb.h>
 
+extern dma_addr_t bad_dma_address;
+
 struct dma_mapping_ops {
 	int             (*mapping_error)(dma_addr_t dma_addr);
 	void*           (*alloc_coherent)(struct device *dev, size_t size,

include/asm-x86/dma-mapping_64.h

 #ifndef _X8664_DMA_MAPPING_H
 #define _X8664_DMA_MAPPING_H 1
 
-extern dma_addr_t bad_dma_address;
 extern int iommu_merge;
 
 static inline int dma_mapping_error(dma_addr_t dma_addr)