On Thu, Jul 12, 2012 at 12:44:16PM -0500, Rob Clark wrote:
From: Rob Clark rob@ti.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 rob@ti.com
I like this and I guess it's an easy way to solve most of our sharing issues with funnier hw. Exporters can then fall back to large allocations, CMA, special-purpose remappes (like the omap tiler) or platform-specific carveout areas (stolen mem for drm/i915). One little thing though:
Could you add a little helper (maybe in a second patch) to dma_buf that walks all currently attached buffers and ORs together all masks and takes the minimum of all other limits for all attached buffers?
Yours, Daniel
include/linux/device.h | 1 + include/linux/dma-mapping.h | 16 ++++++++++++++++ 2 files changed, 17 insertions(+)
diff --git a/include/linux/device.h b/include/linux/device.h index 161d962..3813735 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -568,6 +568,7 @@ struct device_dma_parameters { * sg limitations. */ unsigned int max_segment_size;
- unsigned int max_segment_count; /* zero for unlimited */ unsigned long segment_boundary_mask;
}; diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index dfc099e..f380f79 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -111,6 +111,22 @@ static inline unsigned int dma_set_max_seg_size(struct device *dev, return -EIO; } +static inline unsigned int dma_get_max_seg_count(struct device *dev) +{
- return dev->dma_parms ? dev->dma_parms->max_segment_count : 0;
+}
+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
return -EIO;+}
static inline unsigned long dma_get_seg_boundary(struct device *dev) { return dev->dma_parms ? -- 1.7.9.5
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