Messages in this thread | | | Date | Thu, 19 Jul 2012 13:30:59 +0200 | From | Daniel Vetter <> | Subject | Re: [Linaro-mm-sig] [PATCH] device: add dma_params->max_segment_count |
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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 > > > _______________________________________________ > Linaro-mm-sig mailing list > Linaro-mm-sig@lists.linaro.org > http://lists.linaro.org/mailman/listinfo/linaro-mm-sig
-- Daniel Vetter Mail: daniel@ffwll.ch Mobile: +41 (0)79 365 57 48
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