tracing/events: Add bounce tracing to swiotbl

Ftrace is currently not able to detect when SWIOTLB has to do double buffering.
Under Xen you can only see it indirectly in function_graph, when
xen_swiotlb_map_page() doesn't stop after range_straddles_page_boundary(), but
calls spinlock functions, memcpy() and xen_phys_to_bus() as well. This patch
introduces the swiotlb:swiotlb_bounced event, which also prints out the
following informations to help you find out why bouncing happened:

dev_name: 0000:08:00.0 dma_mask=ffffffffffffffff dev_addr=9149f000 size=32768
swiotlb_force=0

If you use Xen, and (dev_addr + size + 1) > dma_mask, the buffer is out of the
device's DMA range. If swiotlb_force == 1, you should really change the kernel
parameters. Otherwise, the buffer is not contiguous in mfn space.

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
[v1: Don't print 'swiotlb_force=X', just print swiotlb_force if it is enabled]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 4e8686c7e5a4..f0d841907da6 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -38,6 +38,8 @@
 #include <linux/bootmem.h>
 #include <linux/iommu-helper.h>
 
+#include <trace/events/swiotlb.h>
+
 #define OFFSET(val,align) ((unsigned long)      \
                            ( (val) & ( (align) - 1)))
 
@@ -726,6 +728,8 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
         if (dma_capable(dev, dev_addr, size) && !swiotlb_force)
                 return dev_addr;
 
+        trace_swiotlb_bounced(dev, dev_addr, size, swiotlb_force);
+
         /* Oh well, have to allocate and map a bounce buffer. */
         map = map_single(dev, phys, size, dir);
         if (map == SWIOTLB_MAP_ERROR) {