[RFCv3 1/2] device: add dma_params->max_segment_count

Sumit Semwal
2015-01-27T08:26:17Z

From: Rob Clark <robdclark@gmail.com>

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@gmail.com>
[sumits: Minor updates wrt comments]
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
---

v3: include Robin Murphy's fix[1] for handling '0' as a value for
max_segment_count
v2: minor updates wrt comments on the first version

[1]: http://article.gmane.org/gmane.linux.kernel.iommu/8175/

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 fb506738f7b7..a32f9b67315c 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 c3007cb4bfa6..d3351a36d5ec 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)
+{
+ if (dev->dma_parms && dev->dma_parms->max_segment_count)
+ return dev->dma_parms->max_segment_count;
+ return DMA_SEGMENTS_MAX_SEG_COUNT;
+}
+
+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;
+ }
+ return -EIO;
+}
+
static inline unsigned long dma_get_seg_boundary(struct device *dev)
{
return dev->dma_parms ?
--
1.9.1