Hi Sumit,
On 21/01/15 04:16, Sumit Semwal wrote:
From: Rob Clark <robdclark@xxxxxxxxx>
For devices which have constraints about maximum number of segments in
an sglist. For example, a device which could only deal with contiguous
buffers would set max_segment_count to 1.
The initial motivation is for devices sharing buffers via dma-buf,
to allow the buffer exporter to know the constraints of other
devices which have attached to the buffer. The dma_mask and fields
in 'struct device_dma_parameters' tell the exporter everything else
that is needed, except whether the importer has constraints about
maximum number of segments.
Signed-off-by: Rob Clark <robdclark@xxxxxxxxx>
[sumits: Minor updates wrt comments on the first version]
Signed-off-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
---
include/linux/device.h | 1 +
include/linux/dma-mapping.h | 19 +++++++++++++++++++
2 files changed, 20 insertions(+)
diff --git a/include/linux/device.h b/include/linux/device.h
index fb50673..a32f9b6 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -647,6 +647,7 @@ struct device_dma_parameters {
* sg limitations.
*/
unsigned int max_segment_size;
+ unsigned int max_segment_count; /* INT_MAX for unlimited */
unsigned long segment_boundary_mask;
};
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index c3007cb..38e2835 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -154,6 +154,25 @@ static inline unsigned int dma_set_max_seg_size(struct device *dev,
return -EIO;
}
+#define DMA_SEGMENTS_MAX_SEG_COUNT ((unsigned int) INT_MAX)
+
+static inline unsigned int dma_get_max_seg_count(struct device *dev)
+{
+ return dev->dma_parms ?
+ dev->dma_parms->max_segment_count :
+ DMA_SEGMENTS_MAX_SEG_COUNT;
+}
I know this copies the style of the existing code, but unfortunately it
also copies the subtle brokenness. Plenty of drivers seem to set up a
dma_parms struct just for max_segment_size, thus chances are you'll come
across a max_segment_count of 0 sooner or later. How badly is that going
to break things? I posted a fix recently[1] having hit this problem with
segment_boundary_mask in IOMMU code.
+
+static inline int dma_set_max_seg_count(struct device *dev,
+ unsigned int count)
+{
+ if (dev->dma_parms) {
+ dev->dma_parms->max_segment_count = count;
+ return 0;
+ } else
This "else" is just as unnecessary as the other two I've taken out ;)
Robin.
[1]:http://article.gmane.org/gmane.linux.kernel.iommu/8175/
+ return -EIO;
+}
+
static inline unsigned long dma_get_seg_boundary(struct device *dev)
{
return dev->dma_parms ?
--
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