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@xxxxxxxxx> Regards, Hans On 01/27/2015 09:25 AM, Sumit Semwal wrote: > From: Rob Clark <robdclark@xxxxxxxxx> > > 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@xxxxxxxxx> > [sumits: Minor updates wrt comments] > Signed-off-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx> > --- > > 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 ? > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>