[PATCH] dma-debug: Fix dma_debug_entry offset calculation

[Daniel Mentz <danielmentz@google.com>]

dma-debug uses struct dma_debug_entry to keep track of dma coherent
memory allocation requests. The virtual address is converted into a pfn
and an offset. Previously, the offset was calculated using an incorrect
bit mask.  As a result, we saw incorrect error messages from dma-debug
like the following:

"DMA-API: exceeded 7 overlapping mappings of cacheline 0x03e00000"

Cacheline 0x03e00000 does not exist on our platform.

Fixes: 0abdd7a81b7e ("dma-debug: introduce debug_dma_assert_idle()")
Signed-off-by: Daniel Mentz <danielmentz@google.com>
---
 lib/dma-debug.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 8855f01..d34bd24 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -1464,7 +1464,7 @@ void debug_dma_alloc_coherent(struct device *dev, size_t size,
 	entry->type      = dma_debug_coherent;
 	entry->dev       = dev;
 	entry->pfn	 = page_to_pfn(virt_to_page(virt));
-	entry->offset	 = (size_t) virt & PAGE_MASK;
+	entry->offset	 = (size_t) virt & ~PAGE_MASK;
 	entry->size      = size;
 	entry->dev_addr  = dma_addr;
 	entry->direction = DMA_BIDIRECTIONAL;
@@ -1480,7 +1480,7 @@ void debug_dma_free_coherent(struct device *dev, size_t size,
 		.type           = dma_debug_coherent,
 		.dev            = dev,
 		.pfn		= page_to_pfn(virt_to_page(virt)),
-		.offset		= (size_t) virt & PAGE_MASK,
+		.offset		= (size_t) virt & ~PAGE_MASK,
 		.dev_addr       = addr,
 		.size           = size,
 		.direction      = DMA_BIDIRECTIONAL,
-- 
2.6.0.rc2.230.g3dd15c0