swiotlb: Remove the swiotlb variable usage

POWERPC doesn't expect it to be used.

This fixes the linux-next build failure reported by
Stephen Rothwell:

  lib/swiotlb.c: In function 'setup_io_tlb_npages':
  lib/swiotlb.c:114: error: 'swiotlb' undeclared (first use in this function)

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: peterz@infradead.org
LKML-Reference: <20091112000258F.fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/swiotlb.h

@@ -9,11 +9,12 @@ extern int swiotlb_force;
 
 #ifdef CONFIG_SWIOTLB
 extern int swiotlb;
-extern void pci_swiotlb_init(void);
+extern int pci_swiotlb_init(void);
 #else
 #define swiotlb 0
-static inline void pci_swiotlb_init(void)
+static inline int pci_swiotlb_init(void)
 {
+	return 0;
 }
 #endif
 

arch/x86/kernel/pci-dma.c

@@ -125,16 +125,13 @@ static void __init dma32_free_bootmem(void)
 
 void __init pci_iommu_alloc(void)
 {
-	/* swiotlb is forced by the boot option */
-	int use_swiotlb = swiotlb;
 #ifdef CONFIG_X86_64
 	/* free the range so iommu could get some range less than 4G */
 	dma32_free_bootmem();
 #else
 	dma_ops = &nommu_dma_ops;
 #endif
-	pci_swiotlb_init();
-	if (use_swiotlb)
+	if (pci_swiotlb_init())
 		return;
 
 	gart_iommu_hole_init();

arch/x86/kernel/pci-swiotlb.c

@@ -42,16 +42,27 @@ static struct dma_map_ops swiotlb_dma_ops = {
 	.dma_supported = NULL,
 };
 
-void __init pci_swiotlb_init(void)
+/*
+ * pci_swiotlb_init - initialize swiotlb if necessary
+ *
+ * This returns non-zero if we are forced to use swiotlb (by the boot
+ * option).
+ */
+int __init pci_swiotlb_init(void)
 {
 	/* don't initialize swiotlb if iommu=off (no_iommu=1) */
 #ifdef CONFIG_X86_64
 	if (!no_iommu && max_pfn > MAX_DMA32_PFN)
 		swiotlb = 1;
 #endif
+	if (swiotlb_force)
+		swiotlb = 1;
+
 	if (swiotlb) {
 		swiotlb_init(0);
 		dma_ops = &swiotlb_dma_ops;
 	} else
 		dma_ops = &nommu_dma_ops;
+
+	return swiotlb_force;
 }

lib/swiotlb.c

@@ -109,10 +109,9 @@ setup_io_tlb_npages(char *str)
 	}
 	if (*str == ',')
 		++str;
-	if (!strcmp(str, "force")) {
+	if (!strcmp(str, "force"))
 		swiotlb_force = 1;
-		swiotlb = 1;
-	}
+
 	return 1;
 }
 __setup("swiotlb=", setup_io_tlb_npages);