Hi Sumit, Rob,
Is there any reason why this patch hasn't been merged yet? It makes perfect sense to me and I would really like to use this in the media drivers.
Many DMA engines do have a limit to the number of segments (obviously a max count of 1 being the most common limitation, but other limits are definitely possible), so this patch seems a no-brainer to me.
So:
Acked-by: Hans Verkuil hans.verkuil@cisco.com
Regards,
Hans
On 01/27/2015 09:25 AM, Sumit Semwal wrote:
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
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 ?