[PATCH 4/9] swiotlb: remove the overflow buffer

Christoph Hellwig hch at lst.de
Mon Sep 17 08:38:21 PDT 2018


Like all other dma mapping drivers just return an error code instead
of an actual memory buffer.  The reason for the overflow buffer was
that at the time swiotlb was invented there was no way to check for
dma mapping errors, but this has long been fixed.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 arch/arm64/mm/dma-mapping.c       |  2 +-
 arch/powerpc/kernel/dma-swiotlb.c |  4 +--
 include/linux/dma-direct.h        |  2 ++
 include/linux/swiotlb.h           |  3 --
 kernel/dma/direct.c               |  2 --
 kernel/dma/swiotlb.c              | 59 ++-----------------------------
 6 files changed, 8 insertions(+), 64 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index cdcb73db9ea2..abcae73eea50 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -324,7 +324,7 @@ static int __swiotlb_dma_supported(struct device *hwdev, u64 mask)
 static int __swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t addr)
 {
 	if (swiotlb)
-		return swiotlb_dma_mapping_error(hwdev, addr);
+		return dma_direct_mapping_error(hwdev, addr);
 	return 0;
 }
 
diff --git a/arch/powerpc/kernel/dma-swiotlb.c b/arch/powerpc/kernel/dma-swiotlb.c
index 88f3963ca30f..5fc335f4d9cd 100644
--- a/arch/powerpc/kernel/dma-swiotlb.c
+++ b/arch/powerpc/kernel/dma-swiotlb.c
@@ -11,7 +11,7 @@
  *
  */
 
-#include <linux/dma-mapping.h>
+#include <linux/dma-direct.h>
 #include <linux/memblock.h>
 #include <linux/pfn.h>
 #include <linux/of_platform.h>
@@ -59,7 +59,7 @@ const struct dma_map_ops powerpc_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,
-	.mapping_error = swiotlb_dma_mapping_error,
+	.mapping_error = dma_direct_mapping_error,
 	.get_required_mask = swiotlb_powerpc_get_required,
 };
 
diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
index 86a59ba5a7f3..b7984fc78974 100644
--- a/include/linux/dma-direct.h
+++ b/include/linux/dma-direct.h
@@ -5,6 +5,8 @@
 #include <linux/dma-mapping.h>
 #include <linux/mem_encrypt.h>
 
+#define DIRECT_MAPPING_ERROR		0
+
 #ifdef CONFIG_ARCH_HAS_PHYS_TO_DMA
 #include <asm/dma-direct.h>
 #else
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 7ef541ce8f34..f847c1b265c4 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -106,9 +106,6 @@ extern void
 swiotlb_sync_sg_for_device(struct device *hwdev, struct scatterlist *sg,
 			   int nelems, enum dma_data_direction dir);
 
-extern int
-swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr);
-
 extern int
 swiotlb_dma_supported(struct device *hwdev, u64 mask);
 
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index c954f0a6dc62..c22fa0f7c20d 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -13,8 +13,6 @@
 #include <linux/pfn.h>
 #include <linux/set_memory.h>
 
-#define DIRECT_MAPPING_ERROR		0
-
 /*
  * Most architectures use ZONE_DMA for the first 16 Megabytes, but
  * some use it for entirely different regions:
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 69bf305ee5f8..11dbcd80b4a6 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -72,13 +72,6 @@ static phys_addr_t io_tlb_start, io_tlb_end;
  */
 static unsigned long io_tlb_nslabs;
 
-/*
- * When the IOMMU overflows we return a fallback buffer. This sets the size.
- */
-static unsigned long io_tlb_overflow = 32*1024;
-
-static phys_addr_t io_tlb_overflow_buffer;
-
 /*
  * This is a free list describing the number of free entries available from
  * each index
@@ -126,7 +119,6 @@ setup_io_tlb_npages(char *str)
 	return 0;
 }
 early_param("swiotlb", setup_io_tlb_npages);
-/* make io_tlb_overflow tunable too? */
 
 unsigned long swiotlb_nr_tbl(void)
 {
@@ -194,16 +186,10 @@ void __init swiotlb_update_mem_attributes(void)
 	bytes = PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT);
 	set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT);
 	memset(vaddr, 0, bytes);
-
-	vaddr = phys_to_virt(io_tlb_overflow_buffer);
-	bytes = PAGE_ALIGN(io_tlb_overflow);
-	set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT);
-	memset(vaddr, 0, bytes);
 }
 
 int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 {
-	void *v_overflow_buffer;
 	unsigned long i, bytes;
 
 	bytes = nslabs << IO_TLB_SHIFT;
@@ -212,17 +198,6 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 	io_tlb_start = __pa(tlb);
 	io_tlb_end = io_tlb_start + bytes;
 
-	/*
-	 * Get the overflow emergency buffer
-	 */
-	v_overflow_buffer = memblock_virt_alloc_low_nopanic(
-						PAGE_ALIGN(io_tlb_overflow),
-						PAGE_SIZE);
-	if (!v_overflow_buffer)
-		return -ENOMEM;
-
-	io_tlb_overflow_buffer = __pa(v_overflow_buffer);
-
 	/*
 	 * Allocate and initialize the free list array.  This array is used
 	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
@@ -330,7 +305,6 @@ int
 swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 {
 	unsigned long i, bytes;
-	unsigned char *v_overflow_buffer;
 
 	bytes = nslabs << IO_TLB_SHIFT;
 
@@ -341,19 +315,6 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 	set_memory_decrypted((unsigned long)tlb, bytes >> PAGE_SHIFT);
 	memset(tlb, 0, bytes);
 
-	/*
-	 * Get the overflow emergency buffer
-	 */
-	v_overflow_buffer = (void *)__get_free_pages(GFP_DMA,
-						     get_order(io_tlb_overflow));
-	if (!v_overflow_buffer)
-		goto cleanup2;
-
-	set_memory_decrypted((unsigned long)v_overflow_buffer,
-			io_tlb_overflow >> PAGE_SHIFT);
-	memset(v_overflow_buffer, 0, io_tlb_overflow);
-	io_tlb_overflow_buffer = virt_to_phys(v_overflow_buffer);
-
 	/*
 	 * Allocate and initialize the free list array.  This array is used
 	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
@@ -390,10 +351,6 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 	                                                 sizeof(int)));
 	io_tlb_list = NULL;
 cleanup3:
-	free_pages((unsigned long)v_overflow_buffer,
-		   get_order(io_tlb_overflow));
-	io_tlb_overflow_buffer = 0;
-cleanup2:
 	io_tlb_end = 0;
 	io_tlb_start = 0;
 	io_tlb_nslabs = 0;
@@ -407,8 +364,6 @@ void __init swiotlb_exit(void)
 		return;
 
 	if (late_alloc) {
-		free_pages((unsigned long)phys_to_virt(io_tlb_overflow_buffer),
-			   get_order(io_tlb_overflow));
 		free_pages((unsigned long)io_tlb_orig_addr,
 			   get_order(io_tlb_nslabs * sizeof(phys_addr_t)));
 		free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
@@ -416,8 +371,6 @@ void __init swiotlb_exit(void)
 		free_pages((unsigned long)phys_to_virt(io_tlb_start),
 			   get_order(io_tlb_nslabs << IO_TLB_SHIFT));
 	} else {
-		memblock_free_late(io_tlb_overflow_buffer,
-				   PAGE_ALIGN(io_tlb_overflow));
 		memblock_free_late(__pa(io_tlb_orig_addr),
 				   PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
 		memblock_free_late(__pa(io_tlb_list),
@@ -790,7 +743,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 	/* Oh well, have to allocate and map a bounce buffer. */
 	map = map_single(dev, phys, size, dir, attrs);
 	if (map == SWIOTLB_MAP_ERROR)
-		return __phys_to_dma(dev, io_tlb_overflow_buffer);
+		return DIRECT_MAPPING_ERROR;
 
 	dev_addr = __phys_to_dma(dev, map);
 
@@ -801,7 +754,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 	attrs |= DMA_ATTR_SKIP_CPU_SYNC;
 	swiotlb_tbl_unmap_single(dev, map, size, dir, attrs);
 
-	return __phys_to_dma(dev, io_tlb_overflow_buffer);
+	return DIRECT_MAPPING_ERROR;
 }
 
 /*
@@ -985,12 +938,6 @@ swiotlb_sync_sg_for_device(struct device *hwdev, struct scatterlist *sg,
 	swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_DEVICE);
 }
 
-int
-swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
-{
-	return (dma_addr == __phys_to_dma(hwdev, io_tlb_overflow_buffer));
-}
-
 /*
  * Return whether the given device DMA address mask can be supported
  * properly.  For example, if your device can only drive the low 24-bits
@@ -1033,7 +980,7 @@ void swiotlb_free(struct device *dev, size_t size, void *vaddr,
 }
 
 const struct dma_map_ops swiotlb_dma_ops = {
-	.mapping_error		= swiotlb_dma_mapping_error,
+	.mapping_error		= dma_direct_mapping_error,
 	.alloc			= swiotlb_alloc,
 	.free			= swiotlb_free,
 	.sync_single_for_cpu	= swiotlb_sync_single_for_cpu,
-- 
2.18.0




More information about the linux-arm-kernel mailing list