arm64: mm: only initialize swiotlb when necessary

Jisheng Zhang · ctmarinas · commit b67a8b29df7e · 2016-06-21T16:54:53.000+01:00
we only initialize swiotlb when swiotlb_force is true or not all system
memory is DMA-able, this trivial optimization saves us 64MB when
swiotlb is not necessary.

Signed-off-by: Jisheng Zhang &lt;jszhang@marvell.com&gt;
Signed-off-by: Catalin Marinas &lt;catalin.marinas@arm.com&gt;
diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
@@ -19,6 +19,7 @@
 
 #include <linux/gfp.h>
 #include <linux/acpi.h>
+#include <linux/bootmem.h>
 #include <linux/export.h>
 #include <linux/slab.h>
 #include <linux/genalloc.h>
@@ -29,6 +30,8 @@
 
 #include <asm/cacheflush.h>
 
+static int swiotlb __read_mostly;
+
 static pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot,
 				 bool coherent)
 {
@@ -341,6 +344,13 @@ static int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt,
 	return ret;
 }
 
+static int __swiotlb_dma_supported(struct device *hwdev, u64 mask)
+{
+	if (swiotlb)
+		return swiotlb_dma_supported(hwdev, mask);
+	return 1;
+}
+
 static struct dma_map_ops swiotlb_dma_ops = {
 	.alloc = __dma_alloc,
 	.free = __dma_free,
@@ -354,7 +364,7 @@ static struct dma_map_ops swiotlb_dma_ops = {
 	.sync_single_for_device = __swiotlb_sync_single_for_device,
 	.sync_sg_for_cpu = __swiotlb_sync_sg_for_cpu,
 	.sync_sg_for_device = __swiotlb_sync_sg_for_device,
-	.dma_supported = swiotlb_dma_supported,
+	.dma_supported = __swiotlb_dma_supported,
 	.mapping_error = swiotlb_dma_mapping_error,
 };
 
@@ -513,6 +523,9 @@ EXPORT_SYMBOL(dummy_dma_ops);
 
 static int __init arm64_dma_init(void)
 {
+	if (swiotlb_force || max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT))
+		swiotlb = 1;
+
 	return atomic_pool_init();
 }
 arch_initcall(arm64_dma_init);
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
@@ -403,7 +403,8 @@ static void __init free_unused_memmap(void)
  */
 void __init mem_init(void)
 {
-	swiotlb_init(1);
+	if (swiotlb_force || max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT))
+		swiotlb_init(1);
 
 	set_max_mapnr(pfn_to_page(max_pfn) - mem_map);
 

Original file line number	Diff line number	Diff line change
`@@ -403,7 +403,8 @@ static void __init free_unused_memmap(void)`
`403`	`403`	`*/`
`404`	`404`	`void __init mem_init(void)`
`405`	`405`	`{`
`406`		`- swiotlb_init(1);`
	`406`	`+ if (swiotlb_force \|\| max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT))`
	`407`	`+ swiotlb_init(1);`
`407`	`408`
`408`	`409`	`set_max_mapnr(pfn_to_page(max_pfn) - mem_map);`
`409`	`410`