Messages in this thread | | | Date | Thu, 13 Mar 2008 22:47:42 -0600 | From | Grant Grundler <> | Subject | Re: [PATCH 1/4 v4] dma: document dma_{un}map_{single|sg}_attrs() interface |
| |
On Wed, Mar 12, 2008 at 09:01:17PM -0700, akepner@sgi.com wrote: > > Document the new dma_{un}map_{single|sg}_attrs() functions. > > Signed-off-by: Arthur Kepner <akepner@sgi.com> > Acked-by: Jesse Barnes <jesse.barnes@intel.com>
Acked-by: Grant Grundler <grundler@parisc-linux.org>
thanks, grant
> --- > > DMA-API.txt | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > DMA-attributes.txt | 24 +++++++++++++++++++ > 2 files changed, 89 insertions(+) > > diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt > index b939ebb..fdb82b0 100644 > --- a/Documentation/DMA-API.txt > +++ b/Documentation/DMA-API.txt > @@ -395,6 +395,71 @@ Notes: You must do this: > > See also dma_map_single(). > > +dma_addr_t > +dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size, > + enum dma_data_direction dir, > + struct dma_attrs *attrs) > + > +void > +dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr, > + size_t size, enum dma_data_direction dir, > + struct dma_attrs *attrs) > + > +int > +dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl, > + int nents, enum dma_data_direction dir, > + struct dma_attrs *attrs) > + > +void > +dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl, > + int nents, enum dma_data_direction dir, > + struct dma_attrs *attrs) > + > +The four functions above are just like the counterpart functions > +without the _attrs suffixes, except that they pass an optional > +struct dma_attrs*. > + > +struct dma_attrs encapsulates a set of "dma attributes". For the > +definition of struct dma_attrs see linux/dma-attrs.h. > + > +The interpretation of dma attributes is architecture-specific, and > +each attribute should be documented in Documentation/DMA-attributes.txt. > + > +If struct dma_attrs* is NULL, the semantics of each of these > +functions is identical to those of the corresponding function > +without the _attrs suffix. As a result dma_map_single_attrs() > +can generally replace dma_map_single(), etc. > + > +As an example of the use of the *_attrs functions, here's how > +you could pass an attribute DMA_ATTR_FOO when mapping memory > +for DMA: > + > +#include <linux/dma-attrs.h> > +/* DMA_ATTR_FOO should be defined in linux/dma-attrs.h and > + * documented in Documentation/DMA-attributes.txt */ > +... > + > + DECLARE_DMA_ATTRS(attrs); > + dma_set_attr(&attrs, DMA_ATTR_FOO); > + .... > + n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, &attr); > + .... > + > +Architectures that care about DMA_ATTR_FOO would check for its > +presence in their implementations of the mapping and unmapping > +routines, e.g.: > + > +void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr, > + size_t size, enum dma_data_direction dir, > + struct dma_attrs *attrs) > +{ > + .... > + int foo = dma_get_attr(attrs, DMA_ATTR_FOO); > + .... > + if (foo) > + /* twizzle the frobnozzle */ > + .... > + > > Part II - Advanced dma_ usage > ----------------------------- > diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt > index e69de29..a4106ec 100644 > --- a/Documentation/DMA-attributes.txt > +++ b/Documentation/DMA-attributes.txt > @@ -0,0 +1,24 @@ > + DMA attributes > + ============== > + > +This document describes the semantics of the DMA attributes that are > +defined in linux/dma-attrs.h. > + > +DMA_ATTR_BARRIER > +---------------- > + > +DMA_ATTR_BARRIER is a barrier attribute for DMA. DMA to a memory > +region with the DMA_ATTR_BARRIER attribute forces all pending DMA > +writes to complete, and thus provides a mechanism to strictly order > +DMA from a device across all intervening busses and bridges. This > +barrier is not specific to a particular type of interconnect, it > +applies to the system as a whole, and so its implementation must > +account for the idiosyncracies of the system all the way from the > +DMA device to memory. > + > +As an example of a situation where DMA_ATTR_BARRIER would be useful, > +suppose that a device does a DMA write to indicate that data is ready > +and available in memory. The DMA of the "completion indication" could > +race with data DMA. Mapping the memory used for completion indications > +with DMA_ATTR_BARRIER would prevent the race. > +
| |