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Subject[PATCH] arm64: mm: only initialize swiotlb when necessary
Date
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 <jszhang@marvell.com>
---
arch/arm64/mm/dma-mapping.c | 15 ++++++++++++++-
arch/arm64/mm/init.c | 3 ++-
2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index c566ec8..46a4157 100644
--- 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
index d45f862..7d25b4d 100644
--- 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);

--
2.8.1
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