[PATCH RFC] swiotlb: Remove SWIOTLB overflow buffer support

[Shuah Khan <shuah.khan@hp.com>]

Remove SWIOTLB overflow buffer support and return DMA_ERROR_CODE
(a value of zero) to make it consistent with iommu implementation
on Intel, AMD, and swiotlb-xen.

Tested only on x86.

Signed-off-by: Shuah Khan <shuah.khan@hp.com>
---
 lib/swiotlb.c |   44 ++++++++------------------------------------
 1 file changed, 8 insertions(+), 36 deletions(-)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 45bc1f8..7f0a5d1 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -15,6 +15,7 @@
  * 05/09/10 linville	Add support for syncing ranges, support syncing for
  *			DMA_BIDIRECTIONAL mappings, miscellaneous cleanup.
  * 08/12/11 beckyb	Add highmem support
+ * 06/12    shuahkhan	Remove io tlb overflow support
  */
 
 #include <linux/cache.h>
@@ -66,13 +67,6 @@ static char *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 void *io_tlb_overflow_buffer;
-
-/*
  * This is a free list describing the number of free entries available from
  * each index
  */
@@ -108,7 +102,6 @@ setup_io_tlb_npages(char *str)
 	return 1;
 }
 __setup("swiotlb=", setup_io_tlb_npages);
-/* make io_tlb_overflow tunable too? */
 
 unsigned long swiotlb_nr_tbl(void)
 {
@@ -156,12 +149,6 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 	io_tlb_index = 0;
 	io_tlb_orig_addr = alloc_bootmem_pages(PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
 
-	/*
-	 * Get the overflow emergency buffer
-	 */
-	io_tlb_overflow_buffer = alloc_bootmem_low_pages(PAGE_ALIGN(io_tlb_overflow));
-	if (!io_tlb_overflow_buffer)
-		panic("Cannot allocate SWIOTLB overflow buffer!\n");
 	if (verbose)
 		swiotlb_print_info();
 }
@@ -195,7 +182,8 @@ swiotlb_init_with_default_size(size_t default_size, int verbose)
 void __init
 swiotlb_init(int verbose)
 {
-	swiotlb_init_with_default_size(64 * (1<<20), verbose);	/* default to 64MB */
+	/* default to 64MB */
+	swiotlb_init_with_default_size(64 * (1<<20), verbose);
 }
 
 /*
@@ -264,24 +252,12 @@ swiotlb_late_init_with_default_size(size_t default_size)
 
 	memset(io_tlb_orig_addr, 0, io_tlb_nslabs * sizeof(phys_addr_t));
 
-	/*
-	 * Get the overflow emergency buffer
-	 */
-	io_tlb_overflow_buffer = (void *)__get_free_pages(GFP_DMA,
-	                                          get_order(io_tlb_overflow));
-	if (!io_tlb_overflow_buffer)
-		goto cleanup4;
-
 	swiotlb_print_info();
 
 	late_alloc = 1;
 
 	return 0;
 
-cleanup4:
-	free_pages((unsigned long)io_tlb_orig_addr,
-		   get_order(io_tlb_nslabs * sizeof(phys_addr_t)));
-	io_tlb_orig_addr = NULL;
 cleanup3:
 	free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
 	                                                 sizeof(int)));
@@ -297,12 +273,10 @@ cleanup1:
 
 void __init swiotlb_free(void)
 {
-	if (!io_tlb_overflow_buffer)
+	if (!io_tlb_orig_addr)
 		return;
 
 	if (late_alloc) {
-		free_pages((unsigned long)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 *
@@ -310,8 +284,6 @@ void __init swiotlb_free(void)
 		free_pages((unsigned long)io_tlb_start,
 			   get_order(io_tlb_nslabs << IO_TLB_SHIFT));
 	} else {
-		free_bootmem_late(__pa(io_tlb_overflow_buffer),
-				  PAGE_ALIGN(io_tlb_overflow));
 		free_bootmem_late(__pa(io_tlb_orig_addr),
 				  PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
 		free_bootmem_late(__pa(io_tlb_list),
@@ -639,7 +611,7 @@ swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,
 	printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "
 	       "device %s\n", size, dev ? dev_name(dev) : "?");
 
-	if (size <= io_tlb_overflow || !do_panic)
+	if (!do_panic)
 		return;
 
 	if (dir == DMA_BIDIRECTIONAL)
@@ -681,7 +653,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 	map = map_single(dev, phys, size, dir);
 	if (!map) {
 		swiotlb_full(dev, size, dir, 1);
-		map = io_tlb_overflow_buffer;
+		return DMA_ERROR_CODE;
 	}
 
 	dev_addr = swiotlb_virt_to_bus(dev, map);
@@ -691,7 +663,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 	 */
 	if (!dma_capable(dev, dev_addr, size)) {
 		swiotlb_tbl_unmap_single(dev, map, size, dir);
-		dev_addr = swiotlb_virt_to_bus(dev, io_tlb_overflow_buffer);
+		dev_addr = 0;
 	}
 
 	return dev_addr;
@@ -910,7 +882,7 @@ EXPORT_SYMBOL(swiotlb_sync_sg_for_device);
 int
 swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
 {
-	return (dma_addr == swiotlb_virt_to_bus(hwdev, io_tlb_overflow_buffer));
+	return !dma_addr;
 }
 EXPORT_SYMBOL(swiotlb_dma_mapping_error);
 
-- 
1.7.9.5