[RFCv3 1/2] device: add dma_params->max_segment_count
From: m.szyprowski@samsung.com (Marek Szyprowski)
Date: 2015-01-28 20:19:47
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dri-devel, linux-media, linux-mm, lkml
Hello, On 2015-01-27 09:25, Sumit Semwal wrote:
From: Rob Clark <redacted> 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 <redacted> [sumits: Minor updates wrt comments] Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
This feature is definitely needed to start thinking of real buffer sharing between devices. Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
quoted hunk ↗ jump to hunk
--- 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 ?
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland