linux-kernel - [PATCH] device: add dma_params->max_segment

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Date:	Thu, 12 Jul 2012 12:44:16 -0500
From:	Rob Clark <rob.clark@...aro.org>
To:	linux-kernel@...r.kernel.org
Cc:	patches@...aro.org, linaro-mm-sig@...ts.linaro.org,
	Rob Clark <rob@...com>
Subject: [PATCH] device: add dma_params->max_segment_count

From: Rob Clark <rob@...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@...com>
---
 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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