[RFC PATCH 1/7] swiotlb: Instead of tracking the end of the swiotlb region just calculate it

[Alexander Duyck <alexander.h.duyck@intel.com>]

In the case of swiotlb we already have the start of the region and the number
of slabs that give us the region size.  Instead of having to call
virt_to_phys on two pointers we can just take advantage of the fact that the
region is linear and just compute the end based on the start plus the size.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---

 lib/swiotlb.c |   25 ++++++++++++-------------
 1 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index f114bf6..5cc4d4e 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -57,11 +57,11 @@ int swiotlb_force;
  * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
  * API.
  */
-static char *io_tlb_start, *io_tlb_end;
+static char *io_tlb_start;
 
 /*
- * The number of IO TLB blocks (in groups of 64) between io_tlb_start and
- * io_tlb_end.  This is command line adjustable via setup_io_tlb_npages.
+ * The number of IO TLB blocks (in groups of 64).
+ * This is command line adjustable via setup_io_tlb_npages.
  */
 static unsigned long io_tlb_nslabs;
 
@@ -128,11 +128,11 @@ void swiotlb_print_info(void)
 	phys_addr_t pstart, pend;
 
 	pstart = virt_to_phys(io_tlb_start);
-	pend = virt_to_phys(io_tlb_end);
+	pend = pstart + bytes;
 
 	printk(KERN_INFO "software IO TLB [mem %#010llx-%#010llx] (%luMB) mapped at [%p-%p]\n",
 	       (unsigned long long)pstart, (unsigned long long)pend - 1,
-	       bytes >> 20, io_tlb_start, io_tlb_end - 1);
+	       bytes >> 20, io_tlb_start, io_tlb_start + bytes - 1);
 }
 
 void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
@@ -143,12 +143,10 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 
 	io_tlb_nslabs = nslabs;
 	io_tlb_start = tlb;
-	io_tlb_end = io_tlb_start + bytes;
 
 	/*
 	 * Allocate and initialize the free list array.  This array is used
 	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
-	 * between io_tlb_start and io_tlb_end.
 	 */
 	io_tlb_list = alloc_bootmem_pages(PAGE_ALIGN(io_tlb_nslabs * sizeof(int)));
 	for (i = 0; i < io_tlb_nslabs; i++)
@@ -254,14 +252,12 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 
 	io_tlb_nslabs = nslabs;
 	io_tlb_start = tlb;
-	io_tlb_end = io_tlb_start + bytes;
 
 	memset(io_tlb_start, 0, bytes);
 
 	/*
 	 * Allocate and initialize the free list array.  This array is used
 	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
-	 * between io_tlb_start and io_tlb_end.
 	 */
 	io_tlb_list = (unsigned int *)__get_free_pages(GFP_KERNEL,
 	                              get_order(io_tlb_nslabs * sizeof(int)));
@@ -304,7 +300,6 @@ cleanup3:
 	                                                 sizeof(int)));
 	io_tlb_list = NULL;
 cleanup2:
-	io_tlb_end = NULL;
 	io_tlb_start = NULL;
 	io_tlb_nslabs = 0;
 	return -ENOMEM;
@@ -339,8 +334,10 @@ void __init swiotlb_free(void)
 
 static int is_swiotlb_buffer(phys_addr_t paddr)
 {
-	return paddr >= virt_to_phys(io_tlb_start) &&
-		paddr < virt_to_phys(io_tlb_end);
+	phys_addr_t swiotlb_start = virt_to_phys(io_tlb_start);
+
+	return paddr >= swiotlb_start &&
+		paddr < (swiotlb_start + (io_tlb_nslabs << IO_TLB_SHIFT));
 }
 
 /*
@@ -938,6 +935,8 @@ EXPORT_SYMBOL(swiotlb_dma_mapping_error);
 int
 swiotlb_dma_supported(struct device *hwdev, u64 mask)
 {
-	return swiotlb_virt_to_bus(hwdev, io_tlb_end - 1) <= mask;
+	unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT;
+
+	return swiotlb_virt_to_bus(hwdev, io_tlb_start + bytes - 1) <= mask;
 }
 EXPORT_SYMBOL(swiotlb_dma_supported);