| Message ID | 1421813807-9178-2-git-send-email-sumit.semwal@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Sumit, On 21/01/15 04:16, Sumit Semwal wrote: > From: Rob Clark <robdclark@gmail.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 <robdclark@gmail.com> > [sumits: Minor updates wrt comments on the first version] > Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org> > --- > 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 fb50673..a32f9b6 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 c3007cb..38e2835 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) > +{ > + return dev->dma_parms ? > + dev->dma_parms->max_segment_count : > + DMA_SEGMENTS_MAX_SEG_COUNT; > +} I know this copies the style of the existing code, but unfortunately it also copies the subtle brokenness. Plenty of drivers seem to set up a dma_parms struct just for max_segment_size, thus chances are you'll come across a max_segment_count of 0 sooner or later. How badly is that going to break things? I posted a fix recently[1] having hit this problem with segment_boundary_mask in IOMMU code. > + > +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 This "else" is just as unnecessary as the other two I've taken out ;) Robin. [1]:http://article.gmane.org/gmane.linux.kernel.iommu/8175/ > + return -EIO; > +} > + > static inline unsigned long dma_get_seg_boundary(struct device *dev) > { > return dev->dma_parms ? >
Hi Robin! On 22 January 2015 at 00:26, Robin Murphy <robin.murphy@arm.com> wrote: > Hi Sumit, > > > On 21/01/15 04:16, Sumit Semwal wrote: >> >> From: Rob Clark <robdclark@gmail.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 <robdclark@gmail.com> >> [sumits: Minor updates wrt comments on the first version] >> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org> >> --- >> 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 fb50673..a32f9b6 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 c3007cb..38e2835 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) >> +{ >> + return dev->dma_parms ? >> + dev->dma_parms->max_segment_count : >> + DMA_SEGMENTS_MAX_SEG_COUNT; >> +} > > > I know this copies the style of the existing code, but unfortunately it also > copies the subtle brokenness. Plenty of drivers seem to set up a dma_parms > struct just for max_segment_size, thus chances are you'll come across a > max_segment_count of 0 sooner or later. How badly is that going to break > things? I posted a fix recently[1] having hit this problem with > segment_boundary_mask in IOMMU code. > Thanks very much for reviewing this code; and apologies for missing your patch that you mentioned here; sure, I will update my patch accordingly as well. >> + >> +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 > > > This "else" is just as unnecessary as the other two I've taken out ;) > > > Robin. > > [1]:http://article.gmane.org/gmane.linux.kernel.iommu/8175/ > > >> + return -EIO; >> +} >> + >> static inline unsigned long dma_get_seg_boundary(struct device *dev) >> { >> return dev->dma_parms ? >> > > BR, Sumit.
diff --git a/include/linux/device.h b/include/linux/device.h index fb50673..a32f9b6 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 c3007cb..38e2835 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) +{ + return dev->dma_parms ? + dev->dma_parms->max_segment_count : + 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; + } else + return -EIO; +} + static inline unsigned long dma_get_seg_boundary(struct device *dev) { return dev->dma_parms ?